[[படிமம்:Lspn comet halley.jpg|right|250px|கருப்பகுதி இடதுபக்கமிருந்து சூரியனால் ஒளியூட்டப்பட்டுள்ளது. பல்வேறு பொலிவான வளிம், தூசிச் சீறல்கள் தெரிகின்றன.]]

வால்வெள்ளி (comet) பனிக்கட்டியாலான சிறிய சூரியக் குடும்பப் பொருளாகும். இது சூரியனுக்கு நெருக்கமாக கடக்கும்போது சூடாகி வளிமங்களை வெளியிடும். இந்நிகழ்வு வளிமவீசல் அல்லது தாரை எனப்படுகிறது. இது கண்ணுக்குப் புலப்படும் வளிமண்டலம் அல்லது கருப்புறணியை உருவாக்குகிறது. சிலவேளைகளில், இது வால்வெள்ளியின் "வால்" எனப்படுகிறது. இந்நிகழ்வுகள் சூரியக் கதிர்வீச்சும் சூரியக் காற்றும் வால்வெள்ளியின் உட்கரு மீது செலுத்தும் விளைவுகளால் ஏற்படுகின்றன. வால்வெள்ளி உட்கரு சில நூறு மீட்டர்களில் இருந்து பல பத்து கிமீ குறுக்களவில் அமைகிறது. இதில் பனிக்கட்டி, தூசு, சிறிய பாறைத் துகள்கள் ஆகியவை தளர்வாகக் கலந்திருக்கும். வால்வெள்ளியின் கருப்புறணி, புவியின் விட்டத்தைப் போல 15 மடங்காக அமைய, வால் ஒரு வானியல் அலகு அளவுக்குக் கூட நீண்டிருக்கும். போதுமான பொலிவுள்ள வால்வெள்ளியைப் புவியில் இருந்து தொலைநோக்கி இல்லாமலே பார்க்கலாம். வானில் அது  30° வட்டவில்லை (60 நிலாக்கள்) வெட்டும். பல நாகரிகங்களில் தொல்பழங்கால முதலே வால்வெள்ளிகள் நோக்கப்பட்டு பதிவு செய்யப்பட்டுள்ளன.

நமது சூரியக் குடும்பத்தில், வால்வெள்ளிகளின் வட்டணை அல்லது சுற்றுப்பாதை, புளூட்டோவையும் தாண்டிச் செல்கிறது. சூரியக் குடும்பத்தின் உட்பகுதிக்குள் வரும் வால்வெள்ளிகளுள் பெரும்பாலானவை மிக நீண்ட நீள்வட்ட வட்டணையைக் கொண்டுள்ளன. "தூசுப் பனிப்பந்துகள் (dirty snowballs)" என்று பெரும்பாலும் விளிக்கப்படும் வால்வெள்ளிகள், பெருமளவு உறைந்த காபனீரொட்சைட்டும், மீத்தேனும் நீரும் தூசியும் கனிமத்திரளைகளும் கலந்து உருவானவை.

வால்வெள்ளிகள் மிகவும் மையம்பிறழ்ந்த நீள்வட்ட வட்டணைகளைக் கொண்டுள்ளன. இவற்றின் வட்டணை அலைவுநேரம் அகன்ற நெடுக்கம் கொண்டதாகும். இந்நெடுக்கம் பல ஆண்டுகளில் இருந்து பல மில்லியன் ஆண்டுகள் வரை அமையும். சிற்றலைவுநேர வால்வெள்ளிகள் நெப்டியூன் வட்டணைக்கு அப்பால் உள்ள கைப்பர்பட்டையில் இருந்து அல்லது அதைச் சார்ந்த சிதறிய வட்டிலில் இருந்து தோன்றுகின்றன. நெட்டலைவுநேர வால்வெள்ளிகள் கைப்பர்பட்டையின் வெளிப்புறத்தில் இருந்து அடுத்த விண்மீனின் பாதி தொலைவு வரை விரிந்தமையும் ஊர்த் முகிலில் இருந்து தோன்றுவதாகக் கருதப்படுகின்றன. இவை ஈர்ப்பு குற்றலைவுகளால் ஊர்த் முகிலில் இருந்து சூரியனை நோக்கி இயக்குவிக்கப்படுகின்றன, இந்த குற்றலைவுகள் அருகாமையில் உள்ள கடந்தகால, எதிர்கால, அல்லது கடந்துசெல்லும் விண்மீன்களால் உருவாக்கப்படுகின்றன. மீவலைய வால்வெள்ளிகள் உடுக்கன இடைவெளிக்குள் பரந்துபோகும் முன் உட்புறச் சூரியக் குடும்பத்தின் ஊடாகக் கடக்கலாம். அலைவுநேர வால்வெள்ளியின் தோற்றம் வால்வெள்ளியின் மீட்சி எனப்படுகிறது.

சூரிய ஒண்முகில்கள் ஒடுங்கும்போது எஞ்சிய கழிவுகளே வால்வெள்ளிகள் என்று கருதப்படுகின்றன. இத்தகைய ஒண்முகில்களின் வெளி விளிம்புகள், நீர்ம, வளிம நிலையிலன்றித் திண்ம நிலையில் இருக்கக்கூடியதாகவும் போதிய அளவு குளிர்ந்த நிலையில் இருப்பதாகவும் வாதிடப்படுகிறது. வால்வெள்ளிகளைப் பனியால் சூழப்பட்ட சிறுகோள் என வரையறுப்பது சரியல்ல. வால்வெள்ளிகளின் வால் எப்போதும் சூரியனுக்கு எதிர்த் திசையிலேயே காணப்படும். மற்றைய வான்பொருட்கள் போலவே வால்வெள்ளிகளும் சூரியனைச் சுற்றுகின்றன. இதற்கு ஒரு எடுத்துகாட்டு ஆல்லே வால்வெள்ளி ஆகும். இதனை புவியில் இருந்தபடி 76 ஆண்டுகளுக்கு ஒரு முறை நோக்கலாம்/அவதானிக்கலாம்.

விண்வெளியில் மிதக்கிற எரிகல் தூசிகளும், மீத்தேன், சயனோஜன், கரியமில வளிமம், அம்மோனியா, நீராவி ஆகியவை அந்தக் கல்துண்டுகளைச் சுற்றி ஒட்டிக் கொண்டு உறைந்து விடுகின்றன. வால்வெள்ளி சூரியனை அணுகும்போது வால்வெள்ளியிலுள்ள பொருள்கள் ஆவியாகின்றன. சூரியனிலிருந்து வீசுகிற சூரியக் காற்று அந்த ஆவிகளைச் சூரியனுக்கு எதிர்ப்புறமாகத் தள்ளுகிறது. அந்த ஆவிதான் வாலாகத் தோற்றமளிக்கிறது. பல முறை சூரியனைச் சுற்றி வந்தபின் வால்வெள்ளிகளின்  மேற்பரப்பு படலங்களெல்லாம் ஆவியாகிப்போய் வெறும் பாறைத்துண்டு மட்டும் மிஞ்சும். அந்தப் பாறைத்துண்டும் உடைந்து பூமியிலும் மற்ற கோளிலும் எரிகற்களாகப் போய்விழும்.. குறுங்கோள்கள் வால்வெள்ளிகளைப் போல வெளிப்புறச் சூரியக் குடும்பத்துக்குள் தோன்றாமல், வியாழனின் வட்டணைக்கும் உள்ளே அமைந்த பகுதியில் தோன்றுகின்றன. முதன்மைப்பட்டை வால்வெள்ளிகளின் கண்டுபிடிப்பும் முனைப்பான செண்டார் வகை சிறுகோள்களின் கண்டுபிடிப்பும் குறுங்கோளுக்கும் வால்வெள்ளிகளுக்கும் இடையில் அமைந்த வேறுபாட்டை மழுங்கடித்து விட்டன.

2014 நவம்பர் மாதம் வரை 5,253  வால்வெள்ளிகள் அறியப்பட்டுள்ளன. இந்த எண்ணிக்கை வளர்ந்துகொண்டே வருகிறது. வாய்ப்புள்ள மொத்த வால்வெள்ளிகளை ஒப்பிடும்போது இது மிகச் சிறிய திரளேயாகும். வெளிப்புறச் சூரியக் குடும்பத்தில் (ஊர்த் முகிலில்) வால்வெள்ளிபோன்ற வான்பொருள்கள் டிரில்லியன் அளவில் இருப்பதாக மதிப்பிடப்பட்டுள்ளன. ஓராண்டில் ஒரு வால்வெள்ளி கண்ணுக்குப் புலப்படுகிறது. பல மங்கிய  வால்வெள்ளிகள் நமக்குப் புலப்படுவதில்லை. இவற்றில் பொலிவுமிக்கவை "பெருவால்வெள்ளிகள்" எனப்படுகின்றன. வால்வெள்ளிகளைப் பல ஆளில்லாத விண்கலங்கள் சென்று ஆய்ந்துவருகின்றன. எடுத்துகாட்டாக, ஐரோப்பிய முகமையின் உரோசெட்டா திட்டத்தைக் குறிப்பிடலாம். இத்திட்டம் தான் முதன்முதலில் மனிந்திர விண்கலத்தை ஒரு வால்வெள்ளிக்கு அனுப்பியது.European Space Agency, Rosetta's Philae probe lands on comet. நாசாவின் ஆழ்மொத்தல் விண்கலம்  தெம்பெல் 1 வால்வெள்ளியில் உள்ள குழிப்பள்ளத்தை உட்புறக் கூறுபாட்டு ஆராய்ச்சிக்காக தகர்த்தது.

 சொற்பிறப்பியல் comet எனும் சொல் பழைய ஆங்கிலச் சொல்லாகிய cometa என்பதில் இருந்து வந்தது. இது இலத்தீனச் சொல்லான comēta அல்லது comētēs என்பதில் இருந்து கொணரப்பட்டதாகும். இதுவும் பண்டைய கிரேக்கச் சொல்லான κομήτης ("wearing long hair") என்பதன் இலத்தீன் வடிவம் ஆகும். ஆக்சுபோர்டு ஆங்கில அகரமுதலி''  (ἀστὴρ) κομήτης எனும் ஏற்கெனவே கிரேக்க மொழியில்  "நீளமுடி விண்மீன், வால்வெள்ளி" என்ற பொருள்வாய்ந்த சொல்லினைச் சுட்டுகிறது. Κομήτης என்பது κομᾶν ("நீள முடியணிதல்") என்பதில் இருந்து கொணரப்பட்டதாகும். இது κόμη ("தலைமுடி") என்பதில் இருந்து வந்ததாகும்.  இதன் பொருள் "வால்வெள்ளியின் வால்" என்பதாகும்.

வால்வெள்ளிகளுக்கான வானியல் குறியீடு ☄ ஆகும். இது மூன்று மயிரிழை நீட்சிகள் கொண்ட சிறிய வட்டு ஆகும்.

 புறநிலைப் பான்மைகள்

உட்கரு

thumb| 103P/ஆர்ட்லேவின் உட்கரு, பிளையே விண்கலம் எடுத்த படிமம். உட்கருவின் நீளம் 2 கிமீ ஆகும்.

thumb|81P/வைல்டு வால்வெள்ளியின் ஒளிப்பக்க, இருள்பக்கத் தாரைகளும் கூர்ம்பொறுக்கும் உலர்வாக உள்ளன.

வால்வெள்ளியின் திண்ம அகடு உட்கரு எனப்படுகிறது. உட்கருவில் பாறையும் தூசும் பனிக்கட்டியும் கரிம ஈருயிரகி, கரிம ஓருயிரகி, மீத்தேன், அம்மோனியா போன்ற உறைவளிமங்களும் அமைகின்றன. இவை பிரெடு [விப்புள்] படிமம் உருவாகிய பிறகு தூசிப் பனிப்பந்துகள் எனப்படுகின்றன. உயர்தூசு உள்ளடங்கியவை "பனித் தூசுப் பந்துகள்" எனப்படுகின்றன. 2014 இல் நடத்திய ஆய்வுகள் வழியாக வறுத்த பனிக்கட்டிபோல வால்வெள்ளிகள் அமைதல் அறியப்பட்டது. அதாவது இவற்றின் மேற்பரப்பு கரிமச் சேர்மங்களோடு அடர்பனிப் படிகங்களாலும் உள்பனிப்பகுதி மிகவும் குளிர்ச்சியாகவும் குறைந்த அடர்த்தியுடனும் அமைகின்றன என கூறுகின்றன.

thumb|left|போரெல்லி வால்வெள்ளியின் தாரைகள். ஆனால் மேற்பரப்பில் பனிக்கட்டி இல்லை.

உட்கருவின் மேற்பரப்பு பொதுவாக உலர்ந்த தூசு அல்லது பாறையால் ஆகியிருக்கும். எனவே பனிக்கட்டிகள் பல மீட்டர் தடிப்பான மேலோட்டுக்கு அடியில் பொதிந்திருக்கும். இவை ஏற்கெனவே குறிப்பிட்ட வளிமங்களோடு, பலவகை கரிமச் சேர்மங்களையும் கொண்டுள்ளன. இவற்றில் மெத்தனால், நீரகச் சயனைடு, பார்மால்டிகைடு, எத்தனால், ஈத்தேன் போன்றனவும் மேலும் சிக்கலான நெடுந்தொடர் மூலக்கூறுகள் அமைந்த நீரகக் கரிமங்களும் அமினோ அமிலங்களும் அடங்கும். 2009 இல் நாசாவின் விண்மீன் தூசு விண்கலம் கொணர்ந்த வால்வெள்ளித் தூசில் கிளைசைன் எனும் அமினோ அமிலம் இருந்தமை உறுதி செய்யப்பட்டுள்ளது. புவியில் கண்டறிந்த விண்கற்களைப் பற்றிய நாசாவின் ஆய்வுகளில் இருந்து 2011 ஆகத்து மாதம் வெளியாகிய அறிக்கையில், மரபன் (டி. என். ஏ) முன்மரபன் (ஆர். என். ஏ) ஆகிவற்றின் உட்கூறுகளான அடினைனும் குவானைனும் சார்ந்த பிற கரிமச் சேர்மங்களும் குறுங்கோள்களிலும் விண்கற்களிலும்  உருவாகியுள்ளன என முன்மொழியப்பட்டுள்ளது.

வால்வெள்ளி உட்கருவின் வெளிப்பரப்புகள் மிகத் தாழ்ந்த தெறிப்புக் கெழுவை அல்லது எதிர்பலிப்புக் கெழுவைப் பெற்றுள்ளன. சூரியக் குடும்பத்திலேயே இவைதாம் மிகவும் குறைந்த தெறிப்புக் கெழு அமைந்த வான்பொருள்களாகும். கியோட்டோ விண்வெளி ஆய்கலம் ஆலே வால்வெள்ளி உட்கரு தன் மீது விழுந்த ஒளியில் 4% மட்டுமே தெறித்து அனுப்புவதாகவும் ஆழ்விண்வெளி 1 விண்வெளி ஆய்கலம் போரெலி வால்வெள்ளியின் மேற்பரப்பு தன் மீது விழும் ஒளியை 3% அளவுக்குத் தெறித்து அனுப்புவதாகவும் கண்டுபிடித்துள்ளன; நிலக்கீல் தன்மீது விழும் ஒளியை 7% அளவுக்குத் தெறித்து அனுப்புகிறது என்பதோடு இம்மதிப்புகளை ஒப்பிட்டுப் பார்க்கலாம். எனவே, வால்வெள்ளி உட்கருக்களின் கருநிற மேற்பரப்பு சிக்கலான கரிமச் சேர்மங்களைக் கொண்டு அமையலாம். அவற்ரின் மேற்பரப்பில் இருந்து சூரியச் சூடேற்றம் எடைகுறைவான ஆவியாகும் வேதிச் சேர்மங்களை வெளியேற்றி விடுவதால் பெரியக் கரிமச் சேர்மங்கள் மட்டும் எஞ்சுகின்றன. இவை நிலக்கீல் அல்லது பெட்ரோல் அல்லது கரட்டு எண்ணெய் போல அடர்கருப்பாக காணப்படுகின்றன. வால்வெள்ளி மேற்பரப்பின் தாழ் தெறிப்புக் கெழு, அவற்றைச் சூரிய வெப்பத்தை உறிஞ்சவைத்து தாரை உமிழ்வு நிகழ்வை உருவாக்குகிறது.

30 கிமீ ஆரமுள்ள வால்வெள்ளி உட்கருக்களும் நோக்கப்பட்டுள்ளன என்றாலும் அவற்றின் சரியான அளவைக் கண்டுபிடிப்பது அரிதாகும். 322பி/சோகோ வால்வெள்ளீயின் உட்கரு 100 முதல் 200 மீ விட்டத்துடன் அமைகிறது. 100 மீ விட்டத்தை விட சிறிய வால்வெள்ளிகள் நிலவவில்லை எனக் கூருணர்திறக் கருவிகளால் கண்டுபிடிக்கப்பட்டுள்ளது. Known comets have been estimated to have an average density of . வால்வெள்ளிகளின் பொருண்மை மிகக் குறைவாக அமைவதால், தம்முள் ஈர்ப்பால் கோளமாக ஒடுங்காமல் பல வடிவங்களில் அமைகின்றன.

புவியண்மைச் சிறுகோள்களில் 6% சிறுகோள்கள் வளிம உமிழ்வு நின்றுவிட்ட காலாவதியான வால்வெள்ளிகளே எனக் கருதப்படுகின்றன, இவற்றில் 14827 கிப்னோசு, 3552 தான் குவிக்சோட் ஆகிய சிறுகோள்களும் அடங்கும்.

உரோசெட்டா, பிளையே விண்கலங்களின் ஆய்வு முடிவுகள்,  67பி/சூர்யமோவ்- கெராசிமென்கோ வால்வெள்ளியில் காந்தப்புலம் ஏதும் இல்லையென உறுதிப்படுத்தியுள்ளன. எனவே, இந்த வான்பொருள்களின் தொடக்கநிலை உருவாக்கத்தில் காந்தவிசைகள் பங்கேதும் ஆற்றவில்லை என்பது தெளிவாகிறது.

+சில வால்வெள்ளிகளின் இயல்புகள் பெயர் அளவுகள்(கிமீ) அடர்த்தி(கி/செமீ3) பொருண்மை(கிகி)ஆலே:  15×8×8 கிமீ நீள்வட்டப் பருமனையும்*  0.6 கி/செமீ3  கரட்டுக் குத்தூண்அடர்த்தியையும் பயன்படுத்த  (m=d*v),  3.02E+14 கிகி பொருண்மை கிடைக்கிறது.
தெம்பெல் 1:  6.25 கிமீ கோளப் பருமனையும்]] *  0.62 g/ கி/செமீ3 அடர்த்தியையும் பயன்படுத்த 7.9E+13 கிகி பொருண்மை கிடைக்கிறது .
19பி/போரெலி:  8x4x4 கிமீ நீள்வட்டப் பருமனையும் *  0.3 கி/செமீ3  அடர்த்தியையும் பயன்படுத்த 2.0E+13 கிகி பொருண்மை கிடைக்கிறது.
81பி/வைல்டு:  5.5x4.0x3.38x4x4கிமீ நீள்வட்டப் பருமனையும் *  0.6  கி/செமீ3  அடர்த்தியையும் பயன்படுத்த 2.28E+13  கிகி பொருண்மை கிடைக்கிறது.Refs ஆலே வால்வெள்ளி 15 × 8 × 8 0.6 3 தெம்பெல் 1 7.6 × 4.9 0.62 7.9 19பி/போரெலி 8 × 4 × 4 0.3 2.0 81பி/வைல்டு 5.5 × 4.0 × 3.3 0.6 2.3 67பி/சூர்யமோவ்–கெராசிமென்கோ 4.1 × 3.3 × 1.8 0.47 1.0

கருப்புறணி

thumb|அபுள் விண்வெளி தொலைநோக்கி சூரிய அண்மைநிலைக்கு முன் எடுத்த ஐசோன் வால்வெள்ளியின் படிமம்.
வால்கள்

தாரைகள்

வட்டணைப் பான்மைகள்

சிற்றலைவுநேர வால்வெள்ளி

நெட்டலைவுநேர வால்வெள்ளி

காட்சிக்களம்

காணொலிப்படங்கள்

மேலும் காண்க

ஆல்லே வால்வெள்ளி
ஏல்-பாப் வால்வெள்ளி

 மேற்கோள்கள்

 நூல்தொகை

 மேலும் படிக்க

 வெளி இணைப்புகள்
 நிலா முற்ற கட்டுரை

 Comets Page  at NASA's Solar System Exploration
 International Comet Quarterly
 How to Make a Model of a Comet  audio slideshow – National High Magnetic Field Laboratory
 Catalogue of the Solar System Small Bodies Orbital Evolution
 Information about comets and asteroids

*

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Rosetta's frequently asked questions
Why is the mission called Rosetta?
The mission is named after the Rosetta Stone, a slab of volcanic basalt found near the Egyptian town of Rashid (Rosetta) in 1799. The stone revolutionised our understanding of the past. By comparing the three carved inscriptions on the stone (written in two forms of Egyptian and Greek), historians were able to decipher the mysterious hieroglyphics – the written language of ancient Egypt. As a result of this breakthrough, scholars were able to piece together the history of a lost culture.
The Rosetta Stone provided the key to an ancient civilisation. ESA’s Rosetta mission will allow scientists to unlock the mysteries of the oldest building blocks of our Solar System: comets.
When was the mission approved?
The Rosetta Mission was approved as a Cornerstone Mission in ESA's first long-term science programme (Horizon 2000) in November 1993.
What are the mission’s objectives?
Rosetta's prime objective is to help understand the origin and evolution of the Solar System. The comet’s composition reflects the composition of the pre-solar nebula out of which the Sun and the planets of the Solar System formed, more than 4.6 billion years ago. Therefore, an in-depth analysis of comet 67P/Churyumov-Gerasimenko by Rosetta and its lander will provide essential information to understand how the Solar System formed.
There is convincing evidence that comets played a key role in the evolution of the planets, because cometary impacts are known to have been much more common in the early Solar System than today. Comets, for example, probably brought much of the water in today's oceans. They could even have provided the complex organic molecules that may have played a crucial role in the evolution of life on Earth.
What makes the Rosetta mission so special?
Rosetta will be undertaking several ‘firsts’ in space exploration. It will be the first mission to orbit and land on a comet. That makes Rosetta one of the most complex and ambitious missions ever undertaken. Scientists had to plan in advance, in the greatest possible detail, a ten year trip through the Solar System. Approaching, orbiting, and landing on a comet require delicate and spectacular manoeuvres. The comet, 67P/Churyumov-Gerasimenko, is a relatively small object, about 4 kilometres in diameter, moving at a speed as great as 135,000 kilometres per hour. We know very little about its actual surface properties – only when we get there will we be able to explore the surface in such detail that we can choose a safe landing scenario. Rosetta is very special because of the unique science it will perform. No other previous mission has had Rosetta’s potential to look back to the infant Solar System and investigate the role comets may have played in the beginnings of life on Earth.
Rosetta will be the first spacecraft to witness, at close proximity, how a comet changes as it approaches the increasing intensity of the Sun’s radiation. The comet develops the so-called ‘coma’ (essentially the comet’s atmosphere) and the two characteristic ion and dust tails. Rosetta’s lander will obtain the first images from a comet’s surface and make the first in-situ subsurface analysis of its composition.
It will also be the first mission to investigate a comet’s nucleus and environment over an extended period of time.
How did Rosetta reach comet 67P/Churyumov-Gerasimenko, and how long did it take?
Comet 67P/Churyumov-Gerasimenko loops around the Sun between the orbits of Jupiter and Earth, that is, between about 800 million and 186 million kilometres from the Sun. But rendezvousing with the comet required travelling a cumulative distance of over 6.4 billion kilometres. As no launcher was capable of directly injecting Rosetta into such an orbit, gravity assists were needed from four planetary flybys – one of Mars (2007) and three of Earth (2005, 2007 and 2009) – a long circuitous trip that took ten years to complete.
Why is it so important to study comets?
Comets are of great interest to scientists because, to our knowledge, they are the oldest, most primitive bodies in the Solar System, preserving the earliest record of material from the nebula out of which our Sun and planets were formed. Planets have gone through chemical transformations, but comets have remained almost unchanged. Furthermore, comets brought ‘volatile’ light elements to the planets and likely played an important role in forming oceans and atmospheres. Comets also carry complex organic molecules that may have been involved in the origin of life on Earth.
What do we presently know about how the Solar System formed?
The Solar System formed about 5 billion years ago when a cloud of gas and dust – called the ‘pre-solar nebula’ – started to collapse due to gravitational forces. A disc of leftover material made of the same gas and dust present in the primordial cloud formed around the still-forming Sun. After the Sun ‘ignited’ and began its life as star, most of the particles in this disc collided and stuck to one another, growing in size until they became the planets and the other Solar System bodies.
However, it took some time before the Solar System became the way it is now. About 4.5 billion years ago, it was still 'under construction', and interplanetary space was littered with conglomerates of dust particles. Many of these chunks hit the planets and were destroyed in the collision, but thousands of millions of them survived – they are the asteroids and comets we know today.
How will Rosetta be able to gauge the contribution comets made to the beginnings of life on Earth?
Previous studies by ESA’s Giotto spacecraft and ground-based observatories have shown that comets contain complex organic molecules. These are compounds that are rich in carbon, hydrogen, oxygen, and nitrogen. Intriguingly, these are the elements that make up nucleic acids and amino acids, essential ingredients for life as we know it. Did life on Earth begin with the help of comet seeding? Although Rosetta may not give us a definitive answer, it will provide a wealth of information. For example, the mass spectrometers on the orbiter and the lander will analyse, more precisely than ever before, the kind of organic molecules present in the comet. Laboratory simulations of interstellar processes showed that such instruments can detect a variety of amino acids.
How will the mission determine whether comets provided some of the water present in today's oceans?
Rosetta will investigate this by analysing the isotopic abundances in the cometary ices. The isotopes of a certain chemical element are atoms of the same kind that differ slightly in weight. Deuterium, for example, is an isotope of hydrogen; it is also heavier than hydrogen. All the deuterium and hydrogen in the Universe was made just after the Big Bang, about 13.7 billion years ago, fixing the overall ratio between the two kinds of atoms. However, the ratio seen in water can vary from location to location. The chemical reactions involved in making ice in space lead to a higher or lower chance of a deuterium atom replacing one of the two hydrogen atoms in a water molecule, depending on the particular environmental conditions. Thus, by comparing the deuterium to hydrogen ratio found in the water in Earth's oceans with that in extraterrestrial objects, we can try to identify the origin of Earth’s water. For example, if the hydrogen-deuterium ratio in the ocean water is similar to that in the cometary ice, it will support the theory that a fraction of the Earth's water has its origin in space. ESA’s Herschel mission has already found a very similar deuterium-to-hydrogen ratio in comet Hartley-2.
How long will the Rosetta spacecraft operate?
Rosetta’s planned lifetime is about 12 years. The nominal mission ends in December 2015, after the comet reaches its closest point to the Sun (in August 2015) and starts heading back towards the outer Solar System.
How long will the lander operate on the comet nucleus?
The Rosetta lander, called Philae, will touch down on the comet's surface on 12 November 2014. The science observations will start immediately. During the first 2.5 days the first series of scientific measurements will be completed. During this phase the lander will operate on primary battery power. In a second phase that may last up to three months, a secondary set of observations will be conducted, using backup batteries that will be recharged by the energy from the solar cells on the lander. However, no one knows precisely how long the lander will survive on the comet.
Could activity on the comet's surface damage or destroy the lander?
Survival of the lander depends on a number of factors, such as power supply, temperature, or surface activity on the comet. For example, dust may cover the solar panels, preventing the battery from recharging. In any case, by March 2015, when the comet is closer to the Sun, it is likely that the lander will become too hot to operate.
What scientific instruments are on board the spacecraft and what will they do?
Rosetta's goal is to examine the comet in great detail. The instruments on the Rosetta orbiter include several cameras, spectrometers, a number of sensors, and experiments that work at different wavelengths – infrared, ultraviolet, microwave, and radio. They will provide, among other things, very high-resolution images and information about the shape, density, temperature, and chemical composition of the comet. Rosetta’s instruments will analyse the gases and dust grains in the so-called ‘coma' that forms when the comet becomes active, as well as the interaction with the solar wind.
What scientific instruments are on board the lander and what function will they perform?
The 10 instruments on board the lander will do an on-the-spot analysis of the composition and structure of the comet’s surface and subsurface material. A drilling system will obtain samples down to 23 cm below the surface and will feed these to the spectrometers for analysis, such as to determine the chemical composition. Other instruments will measure properties such as near-surface strength, density, texture, porosity, ice phases and thermal properties. Microscopic studies of individual grains will tell us about the texture. In addition, instruments on the lander will study how the comet changes during the day-night cycle, and while it approaches the Sun.
How were the instruments selected?
The most important factors in the selection of each instrument were their expected scientific performance and their technical feasibility. How the instruments fitted together was another consideration, as well as the experience of the team proposing the instrument. This selection was done on the basis of the so-called 'Announcement of Opportunity' (AO) issued by ESA to the scientific community, which is basically an open competition. This AO defines the mission scientific objectives and requirements, and the scientific community had to be compliant with these when submitting their proposals.
How does Rosetta fit into the overall scheme of cometary exploration?
Europe has been a pioneer in exploring comets and asteroids. In 1986, ESA’s Giotto probe flew within 600 kilometres of the comet Halley, closer than any previous spacecraft, and sent back detailed images and data showing, among other things, that comets contain complex organic molecules. Giotto continued its successful journey and in 1992 flew within 200 km of the comet Grigg-Skjellerup, detecting its nucleus. The mission was the first to observe a comet nucleus and confirm theories suggesting that comets were not mere rubble piles or conglomerates of small fragments.
Giotto was part of the five-spacecraft Halley Armada, which also included Russia’s VEGA 1 and 2 spacecraft and two Japanese spacecraft, Susei and Sagigake. Like Giotto, these probes also visited Halley in 1986.
Among other comet missions were a trio of NASA probes: Deep Space 1, which flew by the comet Borelly in 2001; Stardust, which returned samples from the coma of Wild 2 in 2006 and later flew by Tempel 1; and Deep Impact, which in 2005 shot a massive block of copper into the nucleus of Tempel 1 before going on to fly by Hartley 2 and image the comet ISON. Another NASA mission, Contour, launched in Summer 2002, failed when it was incorrectly inserted into its interplanetary trajectory.
Missions have also visited asteroids. In 2005, Japan’s Hayabusa rendezvoused with and landed on the asteroid Itokawa. Six years later, another NASA mission, Dawn, explored the asteroid Vesta. Dawn is now en route to dwarf planet Ceres, which is the largest object in the Asteroid Belt.
What was known about the comet before Rosetta arrived there?
Comet 67P/Churyumov-Gerasimenko orbits the Sun once every 6.6 years. This makes it a short-period comet.
Ground-based telescopes have observed 67P/Churyumov-Gerasimenko during almost all its appearances since its discovery in 1969. To acquire as much information as possible about Rosetta’s target comet, ESA implemented a rigorous ground and space-based observation programme of 67P/Churyumov-Gerasimenko. These observations provided a fairly reliable estimate of the comet’s size – about 4 kilometres in diameter.
Where was 67P/Churyumov-Gerasimenko at the time of the rendezvous?
Rosetta met 67P/Churyumov-Gerasimenko on 6 August 2014 when it was still in the cold regions of the Solar System, 539 million kilometres from the Sun, when the comet and Rosetta were on their return journey back into the inner Solar System.
Was the comet active at the time of rendezvous?
As we expected, the comet was only showing minimal signs of activity at the time of rendezvous.
When comets get close to the Sun, the Sun’s heat 'activates' them. The frozen gases on and below the surface sublimate – they pass directly from the solid to the gaseous state – and the outflowing gas drags small dust grains with it into surrounding space. This creates an atmosphere around the nucleus, known as the coma, and generates a dust tail that streams out behind the comet along its orbit. Rosetta will therefore become the first spacecraft to witness at close quarters the development of a comet's coma and subsequent tails.
When does 67P/Churyumov-Gerasimenko come closest to the Sun?
Comet 67P/Churyumov-Gerasimenko orbits the Sun once every ~6.5 years. The most recent perihelion occurred on 13 August 2015, with the comet (and Rosetta) passing within 186 million kilometres from the Sun (between the orbits of Earth and Mars).
What is the gravity on 67P/Churyumov-Gerasimenko's surface, compared with that on Earth?
Comet 67P/Churyumov-Gerasimenko is so small that its gravitational pull is several hundred thousand times weaker than on Earth. For this reason, the Rosetta lander will touch down at no more than a walking pace. It will need a harpoon to safely anchor it to the comet’s surface and prevent it from bouncing back into space.
Why is the comet called 67P/Churyumov-Gerasimenko?
67P/Churyumov-Gerasimenko is named after its discoverers, Klim Churyumov and Svetlana Gerasimenko, astronomers from Kiev who “spotted” the comet for the first time in 1969 on a photographic plate. The 'P' identifies short-period comets with a well-established orbit around the Sun and that take less than 200 years to complete a solar revolution. The number 67 refers to Churyumov-Gerasimenko's position in the list of catalogued periodic comets. The most famous, Halley, is designated 1P.
How many comets are there in the Solar System?
There are billions of comets in our Solar System, which are typically located in one of two regions. The most distant repository of comets is the Oort cloud, at the edge of the Solar System, 100,000 times more distant from the Sun than the Earth, and which is estimated to contain about 12 billion comets. Closer in, just beyond the orbit of Neptune, is the Kuiper belt, which also contains billions of comets and extends from 30 to 50 times the distance equivalent to the Sun-Earth separation (150 million km, or 1 AU).
Some comets escape from these regions and journey into the inner Solar System. Every year many new comets are discovered in this region, often ‘sungrazers’ spotted by ESA/NASA’s SOHO spacecraft. Sungrazers travel very close to the Sun, and are sometimes partially or completely destroyed in the encounter. Comet ISON is a well-known example of a sungrazing comet.
What is the difference between asteroids and comets?
Comets are typically nicknamed 'dirty ice-balls', whereas asteroids, or minor planets, are known, in very simple terms, as ‘rocks in space’. The size of asteroids typically ranges from a metre to several hundred kilometres across. One of the main differences is that asteroids do not usually contain ‘volatiles’ (substances that sublimate i.e. when heated they pass directly from the solid to the gaseous state). Therefore asteroids do not develop a tail or a coma when they approach the Sun. However, a recent class of object has been discovered in the main asteroid belt that are asteroids behaving like comets, sometimes suddenly sporting a dust tail. These are termed ‘main belt comets’ There is also good evidence that some asteroids are 'dead comets', comets that have lost their volatile materials after many approaches to the Sun.
Who are the Rosetta mission contractors?
Rosetta’s industrial team involves more than 50 contractors from 14 European countries and the United States. The prime spacecraft contractor – the company leading the entire industrial team – is Astrium Germany. Major subcontractors are Astrium UK (spacecraft platform), Astrium France (spacecraft avionics) and Alenia Spazio (assembly, integration and verification).
Who built Rosetta’s instrument and lander package?
The orbiter's scientific payload was provided by scientific consortia from institutes across Europe and the United States.
The lander is provided by a European consortium under the leadership of the German Aerospace Research Institute (DLR). Other members of the consortium are ESA and institutes from Austria, Finland, France, Germany, Hungary, Ireland, Italy, and the United Kingdom.
Was new technology developed for Rosetta and can it be reused for other ESA missions?
The solar cells in Rosetta's solar panels are based on a completely new technology, so-called Low-intensity Low Temperature Cells. Thanks to them, Rosetta is the first space mission to journey beyond the main asteroid belt relying solely on solar cells for power generation. Previous deep-space missions used nuclear RTGs (Radio isotope thermal generators). The new solar cells allow Rosetta to operate over 800 million kilometres from the Sun, where levels of sunlight are only 4% those on Earth. The technology will be available for future deep-space flights, such as ESA’s upcoming Jupiter Icy Moons Explorer.
Systems that control the temperature inside the spacecraft are another example of technological spinoffs from the Rosetta mission. When a spacecraft is near the Sun, overheating is a problem, and can be prevented by using radiators. But in the outer Solar System, the problem is keeping the spacecraft and its subsystems warm. The system devised for Rosetta employs several new techniques, including the installation of louvres over the radiators, to keep spacecraft hardware at proper operating temperatures.
Rosetta also includes a number of highly innovative subsystems, some of which have been reused in other ESA missions, including Mars and Venus Express.
How many people are involved in the Rosetta programme, and how many jobs has it created?
About 2,000 people from industry, ESA and scientific institutions were involved in Rosetta's development. It is difficult to establish exactly how many new jobs were created, but Rosetta has certainly helped contribute to the development of the space sector both from the industrial and the scientific point of view.
Who will obtain data from Rosetta, and how will it be distributed?
Rosetta's Science Ground Segment will be responsible for collecting and distributing the scientific data. The unit will be based at the European Space Operations Centre (ESOC) in Darmstadt, Germany, and at the European Space Astronomy Centre (ESAC) in Villanueva de la Cañada, Madrid, Spain. It will be responsible for the collection of the scientific data received from the spacecraft and its distribution to the principal investigators.
The principal investigators head up the teams building the Rosetta instruments and will have the exclusive right to work with the data for six months. After this period, the data will be stored in ESA’s Planetary Science Archive and made freely available to the world's scientific community.
How big is the spacecraft?
The spacecraft dimensions are 2.8 x 2.1 x 2.0 metres. There are two 14-metre-long solar panels with a total area of 64 square metres. From tip to tip, the spacecraft spans 32 metres.
Rosetta's total launch mass is 3,000 kilograms. The spacecraft carries 1,670 kilograms of propellant and the lander weighs 100 kilograms.
How will Rosetta be powered?
The spacecraft relies entirely on the energy provided by its innovative solar panels for all onboard instruments and subsystems.
What challenges did Rosetta face during its long trip through the Solar System?
Ensuring that the spacecraft could survive the hazards of travelling through deep space for more than 10 years, from the benign environment of near-Earth space to the frigid regions beyond the asteroid belt, was one of the principal challenges of the mission. Temperature control was particularly critical, and the spacecraft was put through stringent pre-launch tests in ESA’s environmental test facilities in the Netherlands to confirm its endurance. These tests involved heating the outside surfaces to more than 150°C and then cooling them to -180°C without damaging the instruments.
Is Rosetta pre-programmed or are commands sent from the ground?
Rosetta is operated from the ground. It was impossible to programme manoeuvres for the whole mission before the launch because this would have entailed adjustments at each stage of the journey. Ground commands are sent periodically to readjust the spacecraft’s trajectory. These take up to 50 minutes to reach the spacecraft, when it is farthest from the Earth.
How does the spacecraft deal with this long time lag?
To compensate for the delay, Rosetta is provided with built-in intelligence to look after itself. This is done by its on-board computers, whose tasks include data management and attitude and orbit control. In the event of problems during the lengthy cruise, experts added backup systems to ensure that the spacecraft could remain operational during critical mission phases. For example, to avoid losing power, the spacecraft automatically positions itself with the solar panels facing the Sun.
Why was it necessary to keep Rosetta in hibernation for 31 months?
To limit its consumption of power and fuel, and to minimise operating costs. During hibernation it was spinning once per minute and faced the Sun, so that its solar panels could receive as much sunlight as possible. Almost all of the electrical systems were switched off, with the exception of the radio receivers, command decoders and power supply.
How far did Rosetta get from the Earth and when did it reach this point?
In mid 2012 Rosetta recorded its maximum distance from the Sun and Earth – about 800 million kilometres and 1 billion kilometres, respectively.
What will happen with Rosetta once the mission is finished, and is an extension envisaged?
Rosetta's nominal mission will end in December 2015 after a total lifetime of 12 years. There could be a six-month extension provided there is fuel remaining, nominal activities are completed by the end of 2015 and additional funds are made available. An extended mission would permit scientists to study additional aspects of comet behaviour, including some that might entail higher risk. A decision on this will be taken in late 2014.
What can the lander tell us about comets that the orbiter cannot?
Using its complement of in-situ instruments, the lander will provide a nucleus-based cross-check for some of the orbiter’s remote measurements. It will also have the unique ability to drill down for samples from below the surface and analyse their mechanical properties on the spot. Furthermore, its camera system, especially the micro cameras, will be capable of imaging the landing site at a higher resolution than the high-resolution camera onboard the orbiter (which already has a resolution of 5 cm per pixel).
What is the difference in research significance between collecting samples from the comet’s tail (like Stardust did) and from the surface?
There are several distinct differences. First of all, samples collected from a comet’s coma do not contain volatiles and have already been transformed. The Stardust samples were slowed down by an aerogel (a kind of foam), causing them to heat up significantly from the sudden deceleration. As a result, the original properties of the volatiles were not preserved. But this was the only way they could be brought back to Earth and studied in a laboratory.
Samples studied by Rosetta’s lander will be fresh, containing volatiles that it will be possible to analyse in-situ (i.e. the samples will be heated in a controlled manner and the transformation analysed by lander instruments).
To summarise, Stardust collected processed material while Rosetta will allow us to analyse unprocessed fresh material still containing volatiles. The science performed by the two missions is thus complementary.
Will the orbiter be able to observe the comet from different angles?
Yes, Rosetta will orbit the nucleus in such a way that it can observe the comet from various angles and altitudes.
Will there be any possibility of adjusting the landing sequence once it is initiated?
No. Once the landing sequence has been defined (release speed, position for release etc.) and initiated, it will not be possible to adjust it. However, it should be recalled that the lander will be released at a height of about 22.5 kilometres from the centre of the comet and will touch down on the comet at walking speed, minimizing the risk of an incident.
What if the lander touches down on a very steep slope and drills itself into an awkward angle, or sinks into porous snow or some other soft material?
The lander is designed so that it can land on a slope of up to 30 degrees. The feet are equipped with large pads to allow the lander to touch down on a soft surface. If the surface is very soft, the lander’s feet may sink into it but sinking will eventually be stopped by the bulkiness of the lander’s body. In all scenarios, the lander is expected to be able to safely transmit its data.
Will the public be able to view high-resolution stereo images of the comet like they now see from Mars Express?
Rosetta will provide images with an even higher resolution than those from the HRSC camera on Mars Express. The difference, however, is that the HRSC was especially designed to take three-dimensional (stereo) images, while Rosetta will only be capable of building pseudo 3-D images by processing images from different viewing angles.
Did engineers have to make any changes to the Rosetta spacecraft or lander to adapt them to the new target comet?
A few minor modifications were made to the orbiter, including the addition of thermal blankets around the thrusters. The landing gear on the lander was modified to ensure a smooth touchdown on 67P/Churyumov-Gerasimenko, which has stronger gravity than the original target.
What happened to the spacecraft during the long launch delay?
The spacecraft remained in Kourou, French-Guiana and was kept in safe storage. The solar arrays and the High-Gain Antenna (HGA) were removed and the fuel was off-loaded. Various maintenance activities were carried out on the spacecraft and some instruments, and new software was uploaded to take into account the new target comet.
Does the Rosetta lander have a name?
Yes, the lander is called "Philae", the name of an island in the Nile region of Egypt. An obelisk found on Philae provided the French historian Jean-Francois Champollion with the final clues for deciphering the hieroglyphs on the Rosetta Stone – thus the mission name.
Were technical difficulties encountered during the development of the lander?
Yes, some problems arose during the design and development stage. The lander is really a mini-spacecraft and development of some systems, in particular the landing gear, proved to be more complicated than originally envisaged. Some of the lander experiments, notably the miniature gas analysers, were also difficult to develop and build, and one was eventually dropped.
ESA set up a special lander task force, in cooperation with lander consortium leader DLR, to resolve these problems. Project management was reinforced, the agency contributed some additional funding and more experts from industry were brought in e.g. from Astrium. In other words, ESA adopted a proactive strategy and the problems were sorted out fairly quickly.
What was ESA’s role in the lander?
As a member of the DLR-led lander consortrium, ESA contributed funding and manpower to the project.
Why is the lander described as a Rosetta experiment when it has ten instruments of its own?
Like the other Rosetta experiments, the lander has a single interface with the spacecraft. When the lander Announcement of Opportunity went out, it was agreed to consider the entire unit as a single instrument.
What is the total mission cost?
The total mission cost of Rosetta is close to 1.4 billion Euros of which the total Philae costs are 220 Million Euros (in 2014 economic conditions) including expenses for the one year launch delay. The mission cost covers development and construction of the spacecraft and all of its instruments, including the lander, together with launch and operations.
Though the total cost is high, this should be put in perspective. The figure is barely half the price of a modern submarine, or three Airbus 380 jumbo jets, and covers a period of almost 20 years, from the start of the project in 1996 through the end of the mission in 2015.
Why spend such a huge amount on public money on studying remote stones in space?
ESA’s task is to explore the unknown. In the case of Rosetta, scientists will be learning about comets, objects that have fascinated mankind for millennia. Comets are thought to be the most primitive objects in the Solar System, the building blocks from which the planets were made. So Rosetta will provide exciting new insights into how the planets (including Earth) were born and how life began.
It is important to consider that what may seem pure science ends up contributing to the store of human knowledge, and the advancement of knowledge always has relevance to everyday life, in the practical as well as the philosophical sense. Many technologies developed for space eventually lead to advances in other areas, though it is very difficult to predict when and how basic knowledge will result in practical benefits. If there had not been a need for particle physicists to share data, there would be no World Wide Web.
There are also direct spin-offs, like Rosetta’s advanced solar cell technology.
ESA is very careful to optimise the financial resources available in order to get the maximum profit, in terms of scientific results, technology and – last but not least – advances for European industry.
The educational fallout from major science endeavours should also not be underestimated. Missions like Rosetta are inspiring and fascinating, and help to get more young people interested in science, including many who may eventually choose a scientific career.
Previous missions like Giotto, Stardust and Deep Impact have already observed comets at close quarters. Why Rosetta?
Rosetta is a much more ambitious and advanced mission than Giotto or any of the previous NASA comet explorers. Its observation phase will last much longer and will not be limited to “snap-shots” from flybys.
Giotto obtained a mass of new information but its period of observation was limited to two short-lived flybys. Stardust captured some excellent black and white images and gathered samples of dust from the comet’s coma. However, it was not designed to provide information on the nature of the nucleus. Deep Impact filled in this missing gap but its instrument package included only cameras and a single infrared spectrometer, so most analysis of the comet’s composition had to be done from the ground.
Unlike these missions, Rosetta will include both an orbiter and a lander and be capable of investigating both the nucleus and the coma over a long period of time. It carries a much more advanced payload than any of its predecessors. The suite of eleven experiments on the orbiter will observe all aspects of the comet from close range over more than a year as it moves along its orbit towards the inner Solar System, permitting scientists to study the composition of the coma and nucleus in great detail. For example, they will be able to examine parent molecules on the comet’s surface that originated from the nucleus that have not yet been modified by the space environment, and survey the complex physical and chemical changes in the nucleus as it is warmed by the Sun.
The ten experiments on the lander, including spectrometers, high-resolution cameras and drill, will permit a more detailed comet investigation than has ever been done before.
Why was 67P/Churyumov-Gerasimenko selected as the target comet instead of Wirtanen?
Both 46P/Wirtanen and 67P/Churyumov-Gerasimenko are periodic comets with fairly similar orbits. This means that their return dates and orbits can be predicted with great accuracy. This enabled us to plan the Rosetta rendezvous mission with Wirtanen years in advance.
However, when we were unable to launch in January 2003, we had to weigh the various mission options, bearing in mind the trajectory, amount of fuel and energy required. We had to look for a comet that would be available when we wanted to launch Rosetta and several periodic comets – including Wirtanen – were identified as possible targets. The targets were selected on the basis of three main criteria: scientific return, technical risk to the spacecraft, and funding.
We eventually opted for 67P/Churyumov-Gerasimenko, which Rosetta could reach with the same version of the Ariane 5 rocket . The other options, including a launch to Wirtanen in 2004, would have required a more powerful launch vehicle, either an Ariane 5 ECA or a Proton.
Comet 67P/Churyumov-Gerasimenko is a larger comet than 46P/Wirtanen, with a nucleus about four kilometres across. It is also much more active when approaching the Sun, creating a greater dust hazard.
There were no major changes to the overall mission profile, although the rendezvous with the comet will now take place in 2014, two years later than planned. The revised mission also required three Earth flybys, instead of two initially foreseen.
When was the launch, and why the long launch delay?
Rosetta was launched on 2 March 2004 atop an Ariane 5 G+ rocket. It had initially been planned to send the probe into orbit in January 2003. However, the Ariane 5 was grounded following the inaugural failure of Arianespace’s new high payload Ariane 5 ECA, on 11 Dec 2002, depriving Rosetta of its launch opportunity to the comet Wirtanen.
What happened after Rosetta woke up from its long hibernation?
Rosetta entered deep space hibernation on 8 June 2011, waking up 31 months later on 20 January 2014, at 18:18 GMT.
At this stage, Rosetta was still 9 million km from its target. From February to April, engineers performed a checkout of the orbiter, the lander, and their respective payloads. The first images of the comet were taken at the end of March, from a distance of 5 million km. Between May and August a series of ten critical manoeuvres were executed to match the spacecraft’s velocity and trajectory with that of the comet. The spacecraft arrived at a distance of 100 km from the comet on 6 August 2014.
An extensive mapping and data-collection campaign took place over the following six weeks to determine a suitable landing site for the mission’s lander, Philae. At the same time, Rosetta moved to within 30 km of the comet, and later to 10 km for closer observation. A landing site located on the comet’s smaller lobe was selected, identified as ‘Site J’.
Landing is scheduled for 12 November. It will take about seven hours for Philae to descend to the surface of the comet, during which it will take images and make measurements of the comet’s environment. After touchdown, the initial battery lifetime of the lander is expected to be about 64 hours. Science measurements will include high-resolution images of the comet, in-situ measurements and extraction and analysis of subsurface samples. Solar illumination conditions and the amount of dust settling on the lander’s solar panels will determine the length of the long term science phase.
Meanwhile Rosetta continues its science mission, following the comet through its closest approach to the Sun on 13 August 2015, and beyond.
What were the critical remaining risks at this stage of the mission?
The primary risk involved the orbiter’s thrusters, which have to perform at lower pressure than planned because of a Reaction Control System leak that occurred in September 2006. Engineers were also concerned about the reaction wheels themselves, which have exhibited some noise. However, contingency testing has demonstrated that the system can be operated in a more efficient operating mode, reducing the wear. Moreover, new software has been developed to allow operation in hybrid mode, which would permit the spacecraft to operate with just two wheels.
All previous deep space probes have used RTGs [Radio-isotope Thermoelectric Generator]. Why did ESA choose not to use them for Rosetta?
ESA has not developed RTG (i.e. nuclear) technology, so the agency decided to develop solar cells that could fill the same function.
The Rosetta spacecraft is scheduled to last for almost 12 years, much of it spent in hibernation. What measures were taken to ensure that it can survive and operate properly under these conditions?
The spacecraft was thoroughly tested to ensure that it can survive long periods of hibernation and carries multiple computers that provide a sophisticated failure recognition and recovery capability. The data management system is highly autonomous with two independent computers, each comprising two separate interchangeable components.
We can upload new enhanced software at any time over the 12-year mission, and the software for each computer is interchangeable. This means that both the Data Management System and the Attitude and Orbit Control subsystem can be run on all processors. If the spacecraft is in serious trouble, it automatically goes into safe mode – with its solar arrays pointing at the Sun.
How will the mission teams – operations, scientists, management etc – be kept together and able to operate efficiently during such a long mission?
We won’t be able to keep the various teams together throughout the mission, so we are creating a database that contains complete information about the spacecraft. This will be available to ensure that the replacement staff has the necessary information about the mission.
The first eight months of the mission involved intensive activity that enabled everyone to become familiar with the spacecraft’s behaviour. Since then we have conducted regular training and communication activities, roughly once every 6-12 months. We also ensured adequate training before each manoeuvre.
A number of younger people have gradually been drafted into the instrument teams, including several principal scientific investigators, to ensure that the necessary “know-how” is passed on to new recruits.
Giotto was sent spinning and nearly destroyed by a dust particle, and other missions like Stardust also encountered considerable high-speed dust. What is to prevent the same thing happening to Rosetta?
Rosetta has very little shielding against dust. However, the relative velocities of the dust particles during the Giotto and Stardust encounters were much higher than will be the case with 67P/Churyumov-Gerasimenko. Giotto flew past Comet Halley at about 70 km/s, and Stardust’s flyby speed was about 6 km/s. In contrast, Rosetta will be orbiting very slowly around the nucleus and the relative velocity of the dust from 67P/Churyumov-Gerasimenko will be much lower.
Given the length of the journey, how could you be sure that the spacecraft/comet rendezvous would take place as planned?
Sophisticated and reliable computer models provided a high precision interplanetary trajectory for the comet rendezvous, and everything necessary was done to ensure that the mission proceeded as planned. When Rosetta neared the comet, we used optical navigation techniques, so it was practically impossible to miss the target.
No spacecraft has ever soft-landed on a comet. What are the risks during such a landing and how are they being minimised?
We have some idea of the risks, but no one knows for sure. This is one of the fascinating aspects of the mission. The density and surface roughness of the nucleus are not really known and its gravity is extremely low. We have tried to compensate for these factors in the design of the lander. There will be two harpoons to anchor it to the surface so that it can be reeled in like a fish on a line. There are also ice screws in each foot, which can be rotated to help to secure the spacecraft on the surface. The lander is also designed to stay upright on a slope of up to 30 degrees.
We will try to ensure an adequate margin of safety by mapping the surface of the nucleus at high resolution (a few cm) during the long orbital observation phase so that we know the size, density, surface roughness and other properties of the nucleus. This will enable us to select a suitable landing site.
Under which circumstances would the mission be considered a failure?
Obviously we are hoping and expecting that the lander will succeed in sending back the first images and in-situ measurements ever obtained from a comet nucleus. However, if it fails, the primary science mission can still continue – the most important, long-term scientific investigations will be done by the eleven experiments on the orbiter. These will enable us to map and characterise the nucleus in unprecedented detail, as well as enable us to gain remarkable new insights into the processes taking place, as the nucleus is warmed by the Sun and becomes increasingly active.
An error was detected in the Huygens probe after it was launched. What measures have you taken to ensure that all systems are properly tested and no similar errors slip through the net for Rosetta?
We have carried out end-to-end tests in order to validate the entire system, especially the lander. And although it is impossible to cater for all eventualities during such a long and complex mission these tests give us considerable confidence in the systems and spacecraft architecture developed for Rosetta.
Beagle 2 was lost at the outset of the Mars Express mission. What lessons were learned from that experience?
Rosetta has some similarities to Mars Express/Beagle 2, in particular the fact that it involves both an orbiter and a lander. As Mars Express has demonstrated, ESA has a successful record of delivering and operating spacecraft in deep space.
However, the Rosetta lander mission differs from Beagle 2 in a number of very important aspects. Beagle 2 followed an “uncontrolled” ballistic trajectory, which meant that it had to be protected by a heatshield against very high temperatures during descent. It also featured a complex landing system, including a parachute and airbags to cushion the impact on touchdown.
The Rosetta lander will not be deployed until the orbiter has mapped the surface of the comet’s nucleus in high resolution and a safe landing site has been chosen. It will be released about 22.5 km from the comet centre (about 20.5 km from the surface) and descent will be very slow and controlled, with a touchdown speed of perhaps one metre per second (less than walking speed).
And since the comet has no atmosphere, the lander will not require a heatshield, parachute or airbag, and there will be no concern about bad weather or high velocity winds.
Since this will be the first time that a soft landing on a comet has ever been attempted, there is always the possibility that some unexpected event may occur. However, the landing procedures have undergone thorough testing on Earth and every precaution has been taken to ensure that the lander remains upright and is able to anchor itself to the surface. The lander will be in communication with the orbiter (and Earth) through most of the descent. However, due to the communication time lag, it will not be possible to intervene in real time during the descent phase.
Were any scientific measurements undertaken during the flybys of Earth and Mars?
Yes, there were some observations during all four flybys. The imaging and plasma instruments were switched on – mainly for calibration – during the Earth flybys. The same instruments (VIRTIS, ALICE and OSIRIS) were turned on for scientific studies during at least a part of the Mars encounter, and the microwave instrument (MIRO) was used to sound the martian atmosphere.
Quite a few asteroids have now been observed at close range by various spacecraft. Why was an asteroid flyby included in the Rosetta mission?
There are still many things we do not know about asteroids, including their differing origins and composition, so we like to take advantage of every opportunity to study them. Rosetta flew by two asteroids in the main asteroid belt – 2867 Steins (in 2008) and 21 Lutetia (in 2010). It also observed an asteroid fragment, P/2010 A2 in 2010, in conjunction with the Hubble Space Telescope.
The Lutetia flyby showed the asteroid to have surprisingly high density and an unusual surface composition previously thought to exist only on large asteroids like Vesta. Steins is the first body in the main asteroid belt found to exhibit a loosely bound rubble-pile structure, and the first E-type asteroid to be observed close-up.
In addition to its scientific value, such information will be of considerable practical use. For example, it will contribute to ESA’s Space Situational programme, which is intended among other things to detect asteroids that pass dangerously close to Earth and help prepare countermeasures to prevent a possible collision.
What part, if any, is NASA playing in the Rosetta mission?
NASA is involved in four experiments – MIRO, ALICE, IES (part of IES-RPC) and part of ROSINA. NASA scientists are principal investigators on two of these (MIRO and ALICE). The MIRO (Microwave Instrument for the Rosetta Orbiter) instrument will be used to determine the comet’s abundance of some major gas species, surface outgassing rate and sub-surface temperature. It was also employed to measure the sub-surface temperatures of asteroids visited by Rosetta and to search for gas around them.
ALICE is an ultraviolet imaging spectrometer that will analyse gases in the coma and tail and measure the comet’s production rates of water, carbon monoxide and carbon dioxide. It will also provide information on the surface composition of the nucleus.
In addition, NASA’s Deep Space Network will provide communications and navigation backup during the mission.
Rosetta was originally going to be a sample return mission. Why was that scrapped?
The main reason was cost. NASA was involved during the early mission definition phase, but then pulled out, making sample return too ambitious for ESA to do alone. Although there is obviously no substitute for retrieving an actual sample for analysis back on Earth, Rosetta’sin situexploration is the next best thing. Moreover, Rosetta will permit scientists to study the evolution of the comet’s nucleus at close quarters, which a return mission could not do. And a sample return mission would not be able to carry as many instruments.
Rosetta was originally supposed to carry a British experiment called Berenice. Why was that experiment removed from the payload?
Britain initially intended to provide two gas analysers – one on the lander and one on the orbiter. This was a very ambitious commitment, particularly since these are very complex instruments. The development programme ran into technical difficulties and in the summer of 2000 it became clear that the UK team did not have the time or the resources to make both instruments. So it was decided to develop only the Ptolemy instrument on the lander.
When Galileo was subjected to a long launch postponement, unexpected problems arose after launch. What precautions were taken to prevent a similar event from happening to Rosetta?
All necessary steps were taken to prevent the launch delay from impacting on the mission. Rosetta was stored in a clean room at Kourou from the moment the decision was made to postpone the launch. We also took the precaution of removing some of the major hardware items, notably the High Gain Antenna (HGA), solar arrays and five of the instruments on the orbiter. Updated software was installed and all flight systems testing revalidated.
Is the spacecraft insured?
No, it is not ESA policy to insure science missions.

|
What Is A Near-Earth Object (NEO)?
|
What Is The Purpose Of The Near-Earth Object Program?
How Many Near-Earth Objects Have Been Discovered So Far?
What Are Asteroids And Comets?
What Are The Differences Between An Asteroid, Comet, Meteoroid, Meteor and Meteorite?
Why Study Asteroids?
Why Study Comets?
What Are Atens, Apollos and Amors?
What Is A Potentially Hazardous Asteroid (PHA)?
What Is A Great Comet?
What Spacecraft Are We Sending To Asteroids & Comets?
Also, see our FAQ on Impact Risk Assessment.
What Is A Near-Earth Object (NEO)?
Near-Earth Objects (NEOs) are comets and asteroids
that have been nudged by the
gravitational attraction of nearby planets into orbits that allow them to enter
the Earth's neighborhood. Composed mostly of water ice with embedded dust
particles, comets originally formed in the cold outer planetary system while
most of the rocky asteroids formed in the warmer inner solar system between the
orbits of Mars and Jupiter.
What Is The Purpose Of The Near-Earth Object Program?
The purpose of the Near-Earth Object Program is to coordinate
NASA-sponsored efforts to detect, track and characterize potentially
hazardous asteroids and comets that could approach the Earth.
The NEO Program will focus on the goal of
locating at least
90 percent of the estimated 1,000 asteroids and comets that approach the
Earth and are larger
than 1 kilometer (about 2/3-mile) in diameter, by the end of the
next decade.
In addition to managing the detection and cataloging of Near-Earth objects,
the NEO Program
office will be responsible for facilitating communications between the
astronomical community
and the public should any potentially hazardous objects be discovered.
How Many Near-Earth Objects Have Been Discovered So Far?
As of September 06, 2010, 7251 Near-Earth objects have been discovered.
Some 816 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger.
Also, 1137 of these NEOs have been classified as
Potentially Hazardous Asteroids (PHAs).
What Are Asteroids And Comets?
Asteroids and comets are believed to be ancient
remnants of the earliest years of the formation of
our solar system more than four billion years ago.
From the beginning of life on Earth to the recent
spectacular impact of Comet Shoemaker-Levy 9 with
Jupiter, these so-called "small bodies" play a key
role in many of the fundamental processes that have
shaped the planetary neighborhood in which we live.
Comets are bodies of ice, rock, and organic
compounds that can be several miles in diameter.
Comets are thought to originate from a region beyond
the orbits of the outermost planets. Scientists
believe that gravitational perturbations
periodically jar comets out of this population,
setting these "dirty snowballs" on orbital courses
that bring them closer to the Sun. Some, called
long-period comets, are in elliptical orbits of the
Sun that take them far out beyond the planets and
back. Others, called short-period comets, travel in
shorter orbits nearer the Sun.
When comets venture into the more intense sunlight
of the inner solar system, the ices in the comet
nucleus begin to vaporize and fall away. The evolved
gas forms a tenuous atmosphere around the nucleus
called a coma, while the dust previously in the
nucleus forms a tail that can be thousands of miles
long and sometimes can be seen from Earth. While
striking the early Earth billions of years ago,
comets are thought to have created major changes to
Earth's early oceans, atmosphere, and climate, and
may have delivered the first carbon-based molecules
to our planet, triggering the process of the origins
of life.
Most asteroids are made of rock, but some are
composed of metal, mostly nickel and iron. They
range in size from small boulders to objects that
are hundreds of miles in diameter. A small portion
of the asteroid population may be burned-out comets
whose ices have evaporated away and been blown off
into space. Almost all asteroids are part of the
Main Asteroid Belt, with orbits in the vast region
of space between Mars and Jupiter.
Some asteroids pass very close to Earth's orbit
around the Sun. Scientists have found evidence that
asteroids have hit our planet in the past. Usually,
asteroids and smaller debris called meteoroids are
too small to survive the passage through Earth's
atmosphere. When these burn up on their descent,
they leave a beautiful trail of light known as a
meteor or "shooting star." Larger asteroids
occasionally crash into Earth, however, and create
craters, such as Arizona's mile-wide Meteor Crater
near Flagstaff. Another impact site off the coast of
the Yucatan Peninsula in Mexico, which is buried by
ocean sediments today, is believed to be a record of
the event that led to the extinction of the
dinosaurs 65 million years ago. Fortunately for us,
these big asteroid impacts are rare. A smaller rocky
meteoroid or comet less than 100 yards in diameter
is believed to have entered the atmosphere over the
Tunguska region of Siberia in 1908. The resulting
shockwave knocked down trees for hundreds of square
miles.
What Are The Differences Between An Asteroid, Comet, Meteoroid, Meteor and Meteorite?
In space, a large rocky body in orbit about the Sun is referred to as an asteroid or minor
planet whereas much smaller particles in orbit about the Sun are referred to as meteoroids.
Once a meteoroid enters the Earth's atmosphere and vaporizes, it becomes a meteor (i.e.,
shooting star). If a small asteroid or large meteoroid survives its fiery passage through the
Earth's atmosphere and lands upon the Earth's surface, it is then called a meteorite.
Cometary debris is the source of most small meteoroid particles. Many comets generate
meteoroid streams when their icy cometary nuclei pass near the Sun and release the dust
particles that were once embedded in the cometary ices. These meteoroid particles then
follow in the wake of the parent comet. Collisions between asteroids in space create
smaller asteroidal fragments and these fragments are the sources of most meteorites that
have struck the Earth's surface.
Because they are readily available for study, many meteorites have already been subjected
to detailed chemical and physical analyses in laboratories. If particular asteroids can be
identified as the sources for some of the well-studied meteorites, a detailed knowledge of
the meteorite's composition and structure will provide important information on the
chemical mixture and conditions from which the parent asteroid formed 4.6 billion years
ago.
Summary Table
|
Asteroid
||
A relatively small, inactive, rocky body orbiting the Sun.
|
|
Comet
||
A relatively small, at times active, object whose ices can vaporize in sunlight
forming an atmosphere (coma) of dust and gas and, sometimes, a tail of dust
and/or gas.
|
|
Meteoroid
||
A small particle from a comet or asteroid orbiting the Sun.
|
|
Meteor
||
The light phenomena which results when
a meteoroid enters the Earth's atmosphere and vaporizes;
a shooting star.
|
|
Meteorite
||
A meteoroid that survives its passage through the Earth's atmosphere and
lands upon the Earth's surface.
|
Why Study Asteroids?
The scientific interest in asteroids is due largely to their status
as the remnant debris from the inner solar system formation process.
Because some of these objects can collide with the Earth, asteroids
are also important for having significantly modified the Earth's
biosphere in the past. They will continue to do so in the future.
In addition, asteroids offer a source of volatiles and an
extraordinarily rich supply of minerals that can be exploited for
the exploration and colonization of our solar system in the
twenty-first century.
Asteroids represent the bits and pieces left over from the process
that formed the inner planets, including Earth. Asteroids are also
the sources of most meteorites that have struck the Earth's surface
and many of these meteorites have already been subjected to detailed
chemical and physical analyses. If certain asteroids can be
identified as the sources for some of the well-studied meteorites,
the detailed knowledge of the meteorite's composition and structure will
provide important information on the chemical mixture, and conditions
from which the Earth formed 4.6 billion years ago. During the early
solar system, the carbon-based molecules and volatile materials that
served as the building blocks of life may have been brought to the
Earth via asteroid and comet impacts. Thus the study of asteroids is
not only important for studying the primordial chemical mixture from
which the Earth formed, these objects may hold the key as to how the
building blocks of life were delivered to the early Earth.
Every day, the Earth is bombarded with more than 100 tons of dust and
sand-size particles.
Many of the incoming particles are so small that they are
destroyed in the Earth's atmosphere before they reach the ground.
These particles are often seen as meteors or shooting stars. The vast
majority of all interplanetary material that reaches the Earth's
surface originates as the collision fragments of asteroids that have
run into one another some eons ago. With an average interval of about
100 years, rocky or iron asteroids larger than about 50 meters would be
expected to reach the Earth's surface and cause local disasters or
produce the tidal waves that can inundate low lying coastal areas.
On an average of every few hundred thousand years or so, asteroids
larger than a mile could cause global disasters. In this case, the
impact debris would spread throughout the Earth's atmosphere so that
plant life would suffer from acid rain, partial blocking of sunlight,
and from the firestorms resulting from heated impact debris raining
back down upon the Earth's surface. The probability of an asteroid
striking the Earth and causing serious damage is very remote but the
devastating consequences of such an impact suggests we should closely
study different types of asteroids to understand their compositions,
structures, sizes, and future trajectories.
The asteroids that are potentially the most hazardous because they
can closely approach the Earth are also the objects that could be
most easily exploited for raw materials. These raw materials could be
used in developing the space structures and in generating the rocket
fuel that will be required to explore and colonize our solar system
in the twenty-first century. By closely investigating the compositions
of asteroids, intelligent choices can be made as to which ones offer
the richest supplies of raw materials. It has been estimated that the
mineral wealth resident in the belt of asteroids between the orbits of
Mars and Jupiter would be equivalent to about 100 billion dollars for
every person on Earth today.
Why Study Comets?
Life on Earth began at the end of a period called the late
heavy bombardment, some 3.8 billion years ago. Before this
time, the influx of interplanetary debris that formed the
Earth was so strong that the proto-Earth was far too hot for
life to have formed. Under this heavy bombardment of asteroids
and comets, the early Earth's oceans vaporized and the fragile
carbon-based molecules, upon which life is based, could not
have survived. The earliest known fossils on Earth date from
3.5 billion years ago and there is evidence that biological
activity took place even earlier - just at the end of the
period of late heavy bombardment. So the window when life
began was very short. As soon as life could have formed on
our planet, it did. But if life formed so quickly on Earth
and there was little in the way of water and carbon-based
molecules on the Earth's surface, then how were these
building blocks of life delivered to the Earth's surface so
quickly? The answer may involve the collision of comets
with the Earth, since comets contain abundant supplies of
both water and carbon-based molecules.
As the primitive, leftover building blocks of the outer solar
system formation process, comets offer clues to the chemical
mixture from which the giant planets formed some 4.6 billion
years ago. If we wish to know the composition of the
primordial mixture from which the major planets formed,
then we must determine the chemical constituents of the
leftover debris from this formation process - the comets.
Comets are composed of significant fractions of water ice,
dust, and carbon-based compounds. Since their orbital paths
often cross that of the Earth, cometary collisions with the
Earth have occurred in the past and additional collisions are
forthcoming. It is not a question of whether a comet will
strike the Earth, it is a question of when the next one will
hit. It now seems likely that a comet or asteroid struck near the Yucatan
peninsula in Mexico some 65 million years ago and caused a
massive extinction of more than 75% of the Earth's living
organisms, including the dinosaurs.
Comets have this strange duality whereby they first brought the
building blocks of life to Earth some 3.8 billion years ago and
subsequent cometary collisions may have wiped out many of the
developing life forms, allowing only the most adaptable species
to evolve further. Indeed, we may owe our preeminence at the top
of Earth's food chain to cometary collisions. A catastrophic
cometary collision with the Earth is only likely to happen at
several million year intervals on average, so we need not be
overly concerned with a threat of this type. However, it is
prudent to mount efforts to discover and study these objects,
to characterize their sizes, compositions and structures and
to keep an eye upon their future trajectories.
As with asteroids, comets are both a potential threat and a
potential resource for the colonization of the solar system in
the twenty first century. Whereas asteroids are rich in the
mineral raw materials required to build structures in space,
the comets are rich resources for the water and carbon-based
molecules necessary to sustain life. In addition, an abundant
supply of cometary water ice can provide copious quantities of
liquid hydrogen and oxygen, the two primary ingredients in
rocket fuel. One day soon, comets may serve as fueling stations
for interplanetary spacecraft.
What Are Atens, Apollos and Amors?
Atens, Apollos and Amors are subgroups of Near-Earth asteroids, and are categorized
by their orbits.
In terms of orbital elements, NEOs are asteroids and comets with perihelion
distance q less than 1.3 AU.
The vast majority of NEOs are asteroids, referred to as Near-Earth Asteroids (NEAs).
NEAs are further divided into the following groups according to their perihelion distance (q), aphelion distance (Q) and
their semi-major axes (a):
|Group
||Description
||Definition
|
|NEAs
||Near-Earth Asteroids
||q<1.3 AU
|
|Atens
||Earth-crossing NEAs with semi-major axes smaller than Earth's
(named after asteroid 2062 Aten).
||a<1.0 AU, Q>0.983 AU
|
|Apollos
||Earth-crossing NEAs with semi-major axes larger than Earth's
(named after asteroid 1862 Apollo).
||a>1.0 AU, q<1.017 AU
|
|Amors
||Earth-approaching NEAs with orbits exterior to Earth's but interior
to Mars' (named after asteroid 1221 Amor).
||a>1.0 AU, 1.017<q<1.3 AU
|
What Is A Potentially Hazardous Asteroid (PHA)?
Potentially Hazardous Asteroids (PHAs) are currently defined
based on parameters that measure the asteroid's potential to make
threatening close approaches to the Earth.
Specifically, all asteroids with a minimum orbit intersection distance
(MOID) of
0.05 AU or less
and an absolute magnitude (H) of 22.0 or less
are considered PHAs.
In other words, asteroids that can't get any closer to the Earth
(i.e. MOID) than 0.05 AU
(roughly 7,480,000 km or 4,650,000 mi)
or are smaller than about 150 m (500 ft) in diameter
(i.e. H = 22.0 with assumed albedo of 13%)
are not considered PHAs.
This ``potential'' to make close Earth approaches does not mean
a
PHA will impact the Earth. It only means there is a possibility
for
such a threat. By monitoring these PHAs and updating their orbits as new
observations become available, we can better predict the close-approach
statistics and thus their Earth-impact threat.
What Spacecraft Are We Sending To Asteroids & Comets?
Comet And Asteroid Mission Summary Table
|
NEAR
|
|
Launch
||
February 17, 1996
|
|
Asteroid Mathilde Flyby
||
June 27, 1997
|
|
Asteroid Eros Initial Flyby
||
December 23, 1998
|
|
Asteroid Eros Rendezvous
||
February 14, 2000
|
|
The NEAR mission flew within 1200 km
of asteroid Mathilde and spent
nearly one year in orbit about asteroid Eros in 2001-2001.
|
|
|
|
DEEP SPACE 1
|
|
Launch
||
October 24, 1998
|
|
Asteroid 9969 Braille Flyby
||
July 28, 1999
|
|
Comet Borrelly Flyby
||
September 22, 2001
|
|
The primary Deep Space 1 mission objectives are
test space technologies.
The spacecraft flew within 2000 km of Comet Borrelly on September 22, 2001.
|
|
|
|
STARDUST
|
|
Launch
||
February 7, 1999
|
|
Comet Wild-2 Flyby
||
January 2, 2004
|
|
Earth Sample Return
||
January 15, 2006
|
|
Comet Tempel 1 Flyby
||
February 14, 2011
|
|
The STARDUST spacecraft imaged the nucleus of Comet Wild-2, collected dust
from both the comet's coma and from interplanetary space and brought these
dust samples back to Earth for study. After its primary mission was completed, the mission was extended to encounter another comet, and renamed to Stardust-NEXT.
|
|
|
|
HAYABUSA
|
|
Launch
||
December 2002
|
|
Asteroid 25143 Itokawa Rendezvous
||
September 2005
|
|
Earth Sample Return
||
June 2010
|
|
A cooperative mission between Japan and the U.S., the Hayabusa spacecraft
orbited a near-Earth asteroid and will return asteroid surface samples to Earth for analysis.
|
|
|
|
ROSETTA
|
|
Launch
||
March 2, 2004
|
|
Comet Churyumov-Gerasimenko Rendezvous
||
May 2014
|
|
After three Earth gravity assists and a Mars gravity assit, the Rosetta
spacecraft will rendezvous with, land upon, the surface of a comet in an
effort to study its composition and structure.
|
|
|
|
DEEP IMPACT/EPOXI
|
|
Launch
||
December 30, 2004
|
|
Comet Tempel 1 Impact/Flyby
||
July 4, 2005
|
|
Comet Hartley 2
||
November 4, 2010
|
|
Deep Impact mission impacted the surface
of Comet Tempel 1. The spacecraft studied the crater formation process and examine
the subsurface structure of one of the solar system's most primitive
objects, a remnant from the outer solar system formation process.
After its encounter with Comet Tempel 1, the mission was renamed to EPOXI, and will flyby
Comet Hartely 2 in late 2010
|
|
|
|
DAWN
|
|
Launch
||
September 27, 2007
|
|
Asteroid Vesta Rendezvous
||
July 2011
|
|
Asteroid Ceres Rendezvous
||
February 2015
|
|
The Dawn mission will orbit two asteroids on
a single voyage.
Ceres and Vesta evolved under radically different circumstances in
different parts of the solar system nearly 4.6 billion years ago.
By
observing both protoplanets with the same set of instruments, Dawn will provide new
insight into the formation and evolution of our solar system.
|
|
|

குறுங்கோள்கள் வால்வெள்ளிகளைப் போல வெளிப்புறச் சூரியக் குடும்பத்துக்குள் தோன்றாமல், வியாழனின் வட்டணைக்கும் உள்ளே அமைந்த பகுதியில் தோன்றுகின்றன.

முதன்மைப்பட்டை வால்வெள்ளிகளின் கண்டுபிடிப்பும் முனைப்பான செண்டார் வகை சிறுகோள்களின் கண்டுபிடிப்பும் குறுங்கோளுக்கும் வால்வெள்ளிகளுக்கும் இடையில் அமைந்த வேறுபாட்டை மழுங்கடித்து விட்டன.

Those who are in the midst of the mountains of the sun, and those who are in the midst of the sun, and those who are in the midst of the sun, and those who are in the midst of the sun, and those who are in the midst of the sun, and those who are in the midst of the sun. It was the first time that the people of the town had been found, and the first time that the people of the town had been found, the first time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found, the second time that the people of the town had been found.

By November 2014 there were 5,253 videos known.

வால்வெள்ளிகள்

அறியப்பட்டுள்ளன

Question: how many videos were there in 2014

By November 2014 there were 5,253 videos known.

Question: when were 5,253 videos released

"2014 நவம்பர்

Question: when were 5,253 videos known

"2014 நவம்பர் மாதம் வரை

Question: in what year were 5,253 videos known

By November 2014 there were 5,253 videos known .

2014 நவம்பர் மாதம் வரை 5,253 வால்வெள்ளிகள் அறியப்பட்டுள்ளன.

2014 நவம்பர் மாதம் வரை 5,253 வால்வெள்ளிகள் அறியப்பட்டுள்ளன.

By November 2014 there were 5,253 videos known.

By November 2014 there were 5,253 videos known.

By November 2014 5,253 volcanoes were known. This number is growing. This is a very small screen when combined with the potential total volcanoes. In the outer solar family (in the face of the day)

வால்வெள்ளிகள்

அறியப்பட்டுள்ளன

வளர்ந்துகொண்டே

வால்வெள்ளிகளை

ஒப்பிடும்போது

குடும்பத்தில்

Question: how many volcanoes are there in the solar system

By November 2014 5,253 volcanoes were known. This number is growing. This is a very small screen when combined with the potential total volcanoes. In the outer solar family (in the face of the day)

how many volcanoes are there in the solar system

Question: where are the most volcanoes found in the solar system

வெளிப்புறச் சூரியக் குடும்பத்தில்

where are the most volcanoes found in the solar system

Question: when were 5,253 volcanoes discovered in the solar system

"2014 நவம்பர்

when were 5,253 volcanoes discovered in the solar system

Question: where are the most volcanoes found in our solar system

வெளிப்புறச் சூரியக் குடும்பத்தில்

where are the most volcanoes found in our solar system

Question: where are most volcanoes found in the earth's solar system

வெளிப்புறச் சூரியக் குடும்பத்தில்

where are most volcanoes found in the earth's solar system

Question: in what year were 5,253 volcanoes known

By November 2014 5,253 volcanoes were known . This number is growing . This is a very small screen when combined with the potential total volcanoes . In the outer solar family ( in the face of the day )

By November 2014 5,253 volcanoes were known. This number is growing. This is a very small screen when combined with the potential total volcanoes. In the outer solar family (in the face of the day)

By November 2014 5,253 volcanoes were known. This number is growing. This is a very small screen when combined with the potential total volcanoes. In the outer solar family (in the face of the day)

Let’s take a look at the plan.

It was the first time that the European Space Agency, Rosetta's Philae probe land on a comet.

Touchdown! Rosetta’s Philae probe lands on comet
ESA’s Rosetta mission has soft-landed its Philae probe on a comet, the first time in history that such an extraordinary feat has been achieved.
After a tense wait during the seven-hour descent to the surface of Comet 67P/Churyumov–Gerasimenko, the signal confirming the successful touchdown arrived on Earth at 16:03 GMT (17:03 CET).
The confirmation was relayed via the Rosetta orbiter to Earth and picked up simultaneously by ESA’s ground station in Malargüe, Argentina and NASA’s station in Madrid, Spain. The signal was immediately confirmed at ESA’s Space Operations Centre, ESOC, in Darmstadt, and DLR’s Lander Control Centre in Cologne, both in Germany.
The first data from the lander’s instruments were transmitted to the Philae Science, Operations and Navigation Centre at France’s CNES space agency in Toulouse.
“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” noted Jean-Jacques Dordain, ESA’s Director General.
“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today.”
“After more than 10 years travelling through space, we’re now making the best ever scientific analysis of one of the oldest remnants of our Solar System,” said Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.
“Decades of preparation have paved the way for today’s success, ensuring that Rosetta continues to be a game-changer in cometary science and space exploration.”
“We are extremely relieved to be safely on the surface of the comet, especially given the extra challenges that we faced with the health of the lander,” said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.
“In the next hours we’ll learn exactly where and how we’ve landed, and we’ll start getting as much science as we can from the surface of this fascinating world.”
Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.
“Rosetta’s journey has been a continuous operational challenge, requiring an innovative approach, precision and long experience,” said Thomas Reiter, ESA Director of Human Spaceflight and Operations.
“This success is testimony to the outstanding teamwork and the unique knowhow in operating spacecraft acquired at the European Space Agency over the decades.”
The landing site, named Agilkia and located on the head of the bizarre double-lobed object, was chosen just six weeks after arrival based on images and data collected at distances of 30–100 km from the comet. Those first images soon revealed the comet as a world littered with boulders, towering cliffs and daunting precipices and pits, with jets of gas and dust streaming from the surface.
Following a period spent at 10 km to allow further close-up study of the chosen landing site, Rosetta moved onto a more distant trajectory to prepare for Philae’s deployment.
Five critical go/no-go decisions were made last night and early this morning, confirming different stages of readiness ahead of separation, along with a final preseparation manoeuvre by the orbiter.
Deployment was confirmed at 09:03 GMT (10:03 CET) at a distance of 22.5km from the centre of the comet. During the seven-hour descent, which was made without propulsion or guidance, Philae took images and recorded information about the comet’s environment.
“One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander’s descent trajectory,” said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.
“Furthermore, we’re performing these operations in an environment that we’ve only just started learning about, 510 million kilometres from Earth.”
Touchdown was planned to take place at a speed of around 1 m/s, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.
But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface. The conditions of landing – including whether or not the thruster performed – along with the exact location of Philae on the comet are being analysed.
The first images from the surface are being downlinked to Earth and should be available within a few hours of touchdown.
Over the next 2.5 days, the lander will conduct its primary science mission, assuming that its main battery remains in good health. An extended science phase using the rechargeable secondary battery may be possible, assuming Sun illumination conditions allow and dust settling on the solar panels does not prevent it. This extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.
Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet’s surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.
The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.
The detailed surface measurements that Philae makes at its landing site will complement and calibrate the extensive remote observations made by the orbiter covering the whole comet.
“Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?” said Matt Taylor, ESA Rosetta project scientist.
“Today’s successful landing is undoubtedly the cherry on the icing of a 4 km-wide cake, but we’re also looking further ahead and onto the next stage of this ground-breaking mission, as we continue to follow the comet around the Sun for 13 months, watching as its activity changes and its surface evolves.”
While Philae begins its close-up study of the comet, Rosetta must manoeuvre from its post-separation path back into an orbit around the comet, eventually returning to a 20 km orbit on 6 December.
Next year, as the comet grows more active, Rosetta will need to step further back and fly unbound ‘orbits’, but dipping in briefly with daring flybys, some of which will bring it within just 8 km of the comet centre.
The comet will reach its closest distance to the Sun on 13 August 2015 at about 185 million km, roughly between the orbits of Earth and Mars. Rosetta will follow it throughout the remainder of 2015, as they head away from the Sun and activity begins to subside.
“It’s been an extremely long and hard journey to reach today’s once-in-a-lifetime event, but it was absolutely worthwhile. We look forward to the continued success of the great scientific endeavour that is the Rosetta mission as it promises to revolutionise our understanding of comets,” said Fred Jansen, ESA Rosetta mission manager.
More about Rosetta
Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta’s Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta is the first mission in history to rendezvous with a comet. It is escorting the comet as they orbit the Sun together, and has deployed a lander to its surface.Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission should become the key to unlocking the history and evolution of our Solar System.
About the European Space Agency
The European Space Agency (ESA) provides Europe’s gateway to space.
ESA is an intergovernmental organisation, created in 1975, with the mission to shape the development of Europe’s space capability and ensure that investment in space delivers benefits to the citizens of Europe and the world.
ESA has 20 Member States: Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxem-bourg, the Netherlands, Norway, Poland, Portugal, Romania, Spain, Sweden, Switzerland and the United Kingdom, of whom 18 are Member States of the EU. Two other Member States of the EU, Hungary and Estonia, are likely soon to become new ESA Member States.
ESA has Cooperation Agreements with six other Member States of the EU. Canada takes part in some ESA programmes under a Cooperation Agreement.
ESA is also working with the EU on implementing the Galileo and Copernicus programmes.
By coordinating the financial and intellectual resources of its members, ESA can undertake programmes and activities far beyond the scope of any single European country.
ESA develops the launchers, spacecraft and ground facilities needed to keep Europe at the forefront of global space activities.
Today, it develops and launches satellites for Earth observation, naviga-tion, telecommunications and astronomy, sends probes to the far reaches of the Solar System and cooperates in the human exploration of space.
Learn more about ESA at www.esa.int
For further information, please contact:
ESA Media Relations Office
Tel: +33 1 53 69 72 99
Email: media@esa.int

இவற்றில் பொலிவுமிக்கவை "பெருவால்வெள்ளிகள்" எனப்படுகின்றன. வால்வெள்ளிகளைப் பல ஆளில்லாத விண்கலங்கள் சென்று ஆய்ந்துவருகின்றன. எடுத்துகாட்டாக, ஐரோப்பிய முகமையின்

உரோசெட்டா திட்டத்தைக் குறிப்பிடலாம்.

இத்திட்டம் தான் முதன்முதலில் மனிந்திர விண்கலத்தை ஒரு வால்வெள்ளிக்கு அனுப்பியது.European Space Agency, Rosetta's Philae probe lands on comet.

They are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones who are the ones. Let’s take a look at the plan. It was the first time that the European Space Agency, Rosetta's Philae probe land on a comet.

It was the first time that the European Space Agency, Rosetta's Philae probe land on a comet.

It is a little bit of a little bit of a little bit of a little bit of a little bit of a little bit.

வால்வெள்ளிகளுக்கான வானியல் குறியீடு ☄ ஆகும். இது மூன்று மயிரிழை நீட்சிகள் கொண்ட சிறிய வட்டு ஆகும்.

வால்வெள்ளிகளுக்கான வானியல் குறியீடு ☄ ஆகும். இது மூன்று மயிரிழை நீட்சிகள் கொண்ட சிறிய வட்டு ஆகும்.

It is a little bit of a little bit of a little bit of a little bit of a little bit of a little bit.

It is a little bit of a little bit of a little bit of a little bit of a little bit of a little bit.

And after that, they will be called the worshippers.

உட்கருவில் பாறையும் தூசும் பனிக்கட்டியும் கரிம ஈருயிரகி, கரிம ஓருயிரகி, மீத்தேன், அம்மோனியா போன்ற உறைவளிமங்களும் அமைகின்றன. இவை பிரெடு [விப்புள்] படிமம் உருவாகிய பிறகு தூசிப் பனிப்பந்துகள் எனப்படுகின்றன.

உட்கருவில் பாறையும் தூசும் பனிக்கட்டியும் கரிம ஈருயிரகி, கரிம ஓருயிரகி, மீத்தேன், அம்மோனியா போன்ற உறைவளிமங்களும் அமைகின்றன. இவை பிரெடு [விப்புள்]

படிமம் உருவாகிய பிறகு தூசிப் பனிப்பந்துகள் எனப்படுகின்றன.

Those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens, and those who are in the heavens. And after that, they will be called the worshippers.

And after that, they will be called the worshippers.

After the creation of the foam, the foam is called the foam; the foam is called the "foam foam."

பனிப்பந்துகள்

எனப்படுகின்றன

உள்ளடங்கியவை

எனப்படுகின்றன

Question: after the creation of what is the foam called

பனிப்பந்துகள்

After the creation of the foam, the foam is called the foam; the foam is called the "foam foam."

after the creation of what is the foam called

Question: what is the name of the foam after it is created

தூசுப் பந்துகள்

what is the name of the foam after it is created

Question: after the creation of the foam, what is the foam called

after the creation of the foam, what is the foam called

Question: after the creation of what is the material called

பனிப்பந்துகள்

after the creation of what is the material called

Question: what is created after the creation of the foam

பனிப்பந்துகள்

what is created after the creation of the foam

Question: after the creation of the foam, what is called

பனிப்பந்துகள்

after the creation of the foam, what is called

After the creation of the foam , the foam is called the foam ; the foam is called the " foam foam . "

படிமம் உருவாகிய பிறகு தூசிப் பனிப்பந்துகள் எனப்படுகின்றன. உயர்தூசு உள்ளடங்கியவை "பனித் தூசுப் பந்துகள்" எனப்படுகின்றன.

படிமம் உருவாகிய பிறகு தூசிப் பனிப்பந்துகள் எனப்படுகின்றன. உயர்தூசு உள்ளடங்கியவை "பனித் தூசுப் பந்துகள்" எனப்படுகின்றன.

After the creation of the foam, the foam is called the foam; the foam is called the "foam foam."

After the creation of the foam, the foam is called the foam; the foam is called the "foam foam."

It is in the midst of the shade, or in the midst of the shade, or in the midst.

Although there is uncertainty as to how bright comet Hale-Bopp will be at perihelion and there is no consensus as to whether or not it will be the "Comet of the Century", it is clear that this it will be a bright comet. Comet P/Halley may have been the most important comet scientifically this century because of the armada of spacecraft and intense ground-based observing effort, and certainly other comets have been better placed in the sky for viewing by the general public (including comet Hyakutake last spring), however, comets which are bright naked eye objects and are visible for several months from the northern hemisphere are very rare! This will make this an important comet both scientifically and for the public no matter what the final brightness. There are many scientific experiments which can only be done with very bright comets, either because we are spreading out the light into very small increments and therefore need a bright object (e.g. spectroscopy), or because the instrument technology is not as advanced as in other areas (e.g. in the infra-red, for detecting molecules).
Some examples of unique science which can only be done with a bright comet are discussed below for the case of comet C/1996 B2 (Hyakutake), and plans for coordinated observations of comet C/1995 O1 (Hale-Bopp) are described.
|Comet||Perihelion Date||Period||Perihelion||Eccentricity||Inclination||Arg. of Perihelion||Ascending Node|
|C/1995 O1||1997 04 01.146||2380 yr||0.914 AU||0.995||89.4||130.591||282.471|
|C/1996 B2||1996 05 01.396||29,270 yr||0.230 AU||0.999||124.9||130.2||187.3|
Jets and Rotation Rate - Observations during early March, 1996 from the European Southern Observatory (ESO; Chile), Pic-du-Midi in France, and other sites showed spectacular curved dust jets which were time-variable. Both the jets and observations made through narrow bandpass filters to isolate the light from either the dust or specific molecules showed that comet Hyakutake's brightness was changing on a timescale of 6.3 hours, probably due to nucleus rotation, and a single strong jet. The image at the right shows a false color image of the comet's inner coma which shows a prominent jet. The image was obtained with the ESO New Technology Telescope on March 19, 1996 (ESO Press Photo 25c/96). See larger version.
Fragmentation - During March, 1996, strong dust jets were reported in the inner coma of comet Hyakutake, and telescopes from sites with high resolution capabilities were reporting "knots" or "flakes" of material o moving away from the nucleus at velocities of 10-20 meters/sec. This type of behavior had not been seen before, but was interpreted as small pieces of the comet's surface flaking off. The image at the left from the Hubble Space Telescope taken on March 25, 1996 shows an image 3340 km across. Pieces which have broken off the comet and are forming their own tails are seen at upper left. Individual fragments could be traced from night to night in the images from the different observatories. See larger version.
Molecule Detection - Perhaps some of the most exciting discoveries with comet Hyakutake were the detections of many new molecules in the coma using radio telescopes and infra-red telescopes. Among the molecules discovered include a large suite of organic compounds such as methanol (CH3OH), methyl cyanide (CH3CN), hydrogen cyanide (HCN), formaldehyde (H2CO), methane (CH4), ethanol and ethane (C2H6). The ethane discovery was particularly exciting as this molecule had never before been seen on a comet. The relative abundance of ethane and methane were consistent with thermodynamic equilibrium, and suggested that they formed in a warm high-pressure region, which is inconsistent with our ideas of how comets formed. It is possible that maybe these comet constituents formed near the giant planets, say in a sub-nebula near Jupiter. However, if this interpretation is not possible, then a revision of the current astrochemical models may be needed since production of these molecules is believed to be inhibited in the ISM.
The Table below highlights some of the observed gases on comet Hyakutake and compares them to what we know about other comets and the ISM. The study of the abundance of many of these molecules, possible only with bright comets in many cases, is contributing greatly to our understanding of the origins of comets.
|Species||T_s*||ISM-Gas||ISM-Dust||Most Comets||P/Halley||Hyakutake||Hale-Bopp||Implications|
|H2O||152||100||100||100||100||100||100||-|
|CH3OH||99||4-5||1||1-5||1.5||0.023||0.049||Consistent with grains in ISM cloud cores|
|HCN||95||2||-||0.02||0.1||-||-||-|
|NH3||78||1||10||0.1-2||0.1-2||0.25||-||Consistent with molecular clouds|
|CO2||72||10||0-3||-||2-4||5||-||-|
|H2CO||64||0.2-1||-||0.5||0-5||0.002||-||Variable in P/Halley|
|CH4||31||0.2-7||0-5||0.02||-||0.7||-||First good detection in Hyakutake|
|CO||25||1000||13||1-7||7||5-5.8||6.4||Distributed source and nuclear source in Halley|
|N2||22||10-1000||-||0.1||5||-||-||-|
|S2||20||-||-||0.03||-||0.01||-||Seen in only 1 comet before|
|C2H6||-||-||-||-||-||0.4||0.13||Could be a lower limit|
|CH4:CO||-||0.001-0.003||0.13-2.4||-||-||0.12||-||-|
At the Lowell Observatory astronomers D. Schleicher, B. Millis and T. Farnham are undertaking an extensive long-term observing campaign of comet Hale-Bopp. Schleicher and Millis are experts in the photometric observation of bright comets, and were key observers in the campaign to determine the rotation period of comet P/Halley when it was near perihelion in 1986.
References
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உட்கருவின் மேற்பரப்பு பொதுவாக உலர்ந்த தூசு அல்லது பாறையால் ஆகியிருக்கும்.

It is in the midst of the shade, or in the midst of the shade, or in the midst. Therefore, the pineapple will be stretched on the surface of a multi-meters stain. This is because it has been brought with a specific light, a multi-meters of crude clothes. In them, the mouth, the length, the sight, the mouth, the mouth, as well as the more complex, the mouth, the mouth, the mouth, the mouth, the mouth, and the mouth.

It is in the midst of the shade, or in the midst of the shade, or in the midst.

We can bring them to the shadows.

கரிமச் சேர்மங்களைக் கொண்டு அமையலாம்.

We can bring them to the shadows. The sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine, the sunshine is the sunshine.

Though 30 km of the original valve body has been identified, it is difficult to find its correct size. 322b/sogo valve body stands at a distance of 100 to 200 m.

உட்கருக்களும்

நோக்கப்பட்டுள்ளன

கண்டுபிடிப்பது

வால்வெள்ளீயின்

விட்டத்துடன்

SOHO's new catch: its first officially periodic comet
It is nothing new for the ESA/NASA Solar and Heliospheric Observatory (SOHO) to discover another comet – it has already found more than 1350. But the latest is a bit different - SOHO had spotted it twice before.
For the first time, SOHO’s Large Angle and Spectrometric Coronagraph Experiment (LASCO) has found a rare type of comet called a periodic comet (which flies by the Sun at regular intervals). While many SOHO comets are believed to be periodic, this is the first one that has been conclusively proven and officially declared as such.
Astronomers have seen thousands of comets but classified only around 190 as periodic. Many more are proposed to be periodic, but they only gain this classification officially if they are seen to follow their orbits around the Sun more than twice, and have orbital periods of less than two hundred years. The most famous periodic comet is Halley’s comet, returning every 76 years, with its last close pass to the Sun taking place in 1986.
SOHO’s new catch has a much smaller orbit, taking approximately four years to travel once around the Sun. It was first seen in September 1999, and then again in September 2003. In 2005, German PhD student Sebastian Hoenig realised that the two comets were so similar in orbit that they might actually be the same object.
To test his theory, he calculated a combined orbit for the comet, and consequently predicted that it would return on 11 September 2007. Sebastian's prediction proved to be extremely accurate – the comet reappeared in SOHO's LASCO camera right on schedule, and has now been given the official designation of P/2007 R5 (SOHO).
There is a puzzling aspect, however, as the comet does not look exactly like a comet. It has no visible tail or coma of dust and gas. Initially, some scientists wondered if it were actually an asteroid, a chunk of space-rock rather than a chunk of space-ice. However, P/2007 R5 (SOHO) did exhibit some cometary characteristics. As it passed to within 7.9 million kilometres of the Sun, around 5% of the distance from the Earth to the Sun, they observed it brighten by a factor of around a million. This is common behaviour for a comet.
So P/2007 R5 (SOHO) seems to behave like a comet, even though it doesn’t really look like one. “It is quite possibly an extinct comet nucleus of some kind,” says Karl Battams, who runs SOHO's comet discovery programme. Extinct comets are those that have expelled most of their volatile ice and have little left to form a tail or coma. They are theorised to be common objects amongst the celestial bodies orbiting close to the Sun.
The comet faded as quickly as it brightened, and soon became too faint for SOHO's instruments to see it. Estimates show that P/2007 R5 (SOHO) is probably only 100-200 metres in diameter. Given how small and faint this object is, and how close it still is to the Sun, it is an extremely difficult target for observers on Earth to pick out in the sky.
Now we know for certain that P/2007 R5 (SOHO) is there, astronomers will be watching closely for it during its next return in September 2011.
Notes for editors:
The credit for discovery and recovery of the object goes to Terry Lovejoy (Australia, 1999), Kazimieras Cernis (Lithuania, 2003) and Bo Zhou (China, 2007).
Hoenig’s work is detailed in ‘Identification of a new short-period comet near the Sun’ by S.F. Hoenig, published in Astronomy and Astrophysics in January 2006.
The comet’s properties were confirmed last week by Karl Battams.
For more information
Karl Battams, Naval Research Laboratory, USA
Email: Karl.Battams @ nrl.navy.mil
Bernhard Fleck, ESA SOHO Project Scientist
Email: Bfleck @ esa.nascom.nasa.gov

Question: how much of the original valve body has been identified

Though 30 km of the original valve body has been identified, it is difficult to find its correct size. 322b/sogo valve body stands at a distance of 100 to 200 m.

how much of the original valve body has been identified

Question: what is the range of a 322b/sogo valve body

100 முதல் 200 மீ

what is the range of a 322b/sogo valve body

Question: what is the maximum size of a valve body

322பி / சோகோ

what is the maximum size of a valve body

Question: what is the maximum distance a 322b valve body can reach

what is the maximum distance a 322b valve body can reach

Question: what is the problem with finding the original valve body

it is difficult to find its correct size

என்றாலும் அவற்றின் சரியான அளவைக் கண்டுபிடிப்பது அரிதாகும்

it is difficult to find its correct size

what is the problem with finding the original valve body

Question: what is difficult to find in the original valve body

சரியான அளவைக்

what is difficult to find in the original valve body

Though 30 km of the original valve body has been identified , it is difficult to find its correct size . 322b / sogo valve body stands at a distance of 100 to 200 m.

30 கிமீ ஆரமுள்ள வால்வெள்ளி உட்கருக்களும் நோக்கப்பட்டுள்ளன என்றாலும் அவற்றின் சரியான அளவைக் கண்டுபிடிப்பது அரிதாகும். 322பி/சோகோ வால்வெள்ளீயின் உட்கரு 100 முதல் 200 மீ விட்டத்துடன் அமைகிறது.

30 கிமீ ஆரமுள்ள வால்வெள்ளி உட்கருக்களும் நோக்கப்பட்டுள்ளன என்றாலும் அவற்றின் சரியான அளவைக் கண்டுபிடிப்பது அரிதாகும். 322பி/சோகோ வால்வெள்ளீயின் உட்கரு 100 முதல் 200 மீ விட்டத்துடன் அமைகிறது.

Though 30 km of the original valve body has been identified, it is difficult to find its correct size. 322b/sogo valve body stands at a distance of 100 to 200 m.

Though 30 km of the original valve body has been identified, it is difficult to find its correct size. 322b/sogo valve body stands at a distance of 100 to 200 m.

Known comets have been estimated to have an average density of . if the material of the valve is set very low, the injection of the comet is set in a number of modes without the coat.

வால்வெள்ளிகளின்

[133] Given that there are thousands of asteroids and probably a hundred thousand million comets, these small bodies must be considered essential components of the solar system. Certainly objects closely similar to the small bodies that remain today were involved in the agglomeration of the larger planets and satellites some 4.5 billion years ago, and much of the importance of the small bodies today derives from the clues that they may contain about the processes that took place in the early solar system. This importance is magnified when we realize that asteroid-like parent bodies are the only solar system objects (other than Earth and the Moon) of which we have samples for detailed laboratory studies.
Although our understanding of small bodies is relatively limited, we know enough to realize that geologically these objects are best studied separately from the larger bodies, such as Earth and the Moon. For one thing, gravity is so much smaller on these bodies that it is difficult to extrapolate our experiences with surface processes on larger objects with any great confidence. For another, many of the small objects are irregular and call for mapping and geodetic techniques quite distinct from those commonly used for the larger (usually almost spherical) planets and satellites.
7.1. What is a Small Body?
It is not easy (nor is it necessary) to give a rigorous definition of a small body. Certainly implicit in the term is that the object has a low surface gravity and small escape velocity. Rather arbitrarily, we can take the largest small body to be the size of the biggest asteroid, Ceres, which has a diameter of some 1000 km. Most small bodies are considerably smaller; the two satellites of Mars, Phobos (21 km) and Deimos (12 km), are more representative.
[134] For an object the size of Phobos, surface gravity is only about 1 cm sec-2, and the escape velocity is some 10 m sec-1. Weak gravity has several important implications. Since such bodies cannot have atmospheres, their regoliths are immune to weathering processes involving the presence of an atmosphere. On the other hand, they are directly exposed to the whole spectrum of meteoroidal impacts, cosmic rays, solar radiation, and the solar wind. Low gravity also makes it impossible for the body to achieve or retain a spherical shape during its history, and many small bodies tend to be irregular in shape. Additionally, low gravity affects the development of the surface under meteoroidal bombardment. Craters probably tend to remain deeper, ejecta become more dispersed, and the proportion of strongly shocked material retained is smaller than on larger bodies. Furthermore, the chances that an asteroid-like small body will suffer a catastrophic, or nearly catastrophic, impact during its history are non-negligible.
The study of meteorites has provided incontrovertible proof that some small parent bodies underwent differentiation (Dodd, 1981). In addition, there is strong evidence of subsurface aqueous processes in some parent bodies (Kerridge and Bunch, 1979) and of surface eruptions of lavas on others (Drake, 1979). The realization of the importance of short-lived nuclides such as 26AI as possible heat sources early in the solar system's history has made it quite plausible that some small bodies should have had early histories of melting and other internal activity (Sonett and Reynolds, 1979). Thus, whereas some small bodies (comet nuclei?) may have had dull evolutionary histories and may rightly be regarded as primitive, others have probably experienced histories almost as complex and certainly as interesting as some larger objects.
7.2. Inventory
The solar system's small bodies can be divided conveniently into three broad categories: (1) rocky objects (asteroids and some small satellites), (2) icy objects (mostly small satellites, but perhaps including such objects as Chiron), and (3) comet nuclei.
The inventory of known small bodies includes thousands of asteroids in the main belt, as well as about 60 Amor, Apollo, and Aten objects. Only about 35 asteroids are larger than 200 km across, although physical measurements have been made of objects as small as 200 meters (Gehrels, 1979). None has yet been studied by spacecraft.
The inventory also includes the small satellites of Mars and of the outer planets. Phobos and Deimos, the two tiny satellites of Mars, are the only very small bodies that have been investigated sufficiently by spacecraft (Mariner 9 and Viking) to permit meaningful discussions of surface geologic processes (Veverka and Thomas, 1979).
Jupiter has at least a dozen small satellites. Except for a few low-resolution images of Amalthea obtained by Voyager, we know [136] almost nothing about the geology of these bodies. There are also at least 70 known Trojan asteroids near the libration points of Jupiter's orbit, and speculations exist that some of Jupiter's outer satellites may be related to them (Degewij and van Houten, 1979).
Recent Earth-based and Voyager observations have greatly expanded our list of Saturn's small satellites, and at least in the case of Mimas and Enceladus, the Voyager data are adequate to support geologic investigation. Beyond Saturn, most of the satellites of Uranus, Neptune's Nereid, and Pluto's Charon probably fall within our definition of small bodies. However, it will be at least 1986 before any spacecraft data on any of these objects are available.
It is worthwhile to stress that the above list is almost certainly incomplete and that new small bodies will continue to be discovered. In addition, there are indications that small, so far undetected satellites are associated with the rings of Uranus and perhaps those of Saturn and Jupiter as well.
Comets are the most abundant small bodies in the solar system: one estimate is that some 1011 exist in the Oort cloud at the fringes of the solar system (Wilkening, 1982). From the geologic point of view, it is only the nuclei of comets that are of interest and not the comas and tails that develop when the nucleus approaches close enough to the Sun for its surface ices to vaporize. Most comet nuclei are believed to be bodies of rock and ice less than 10 km across, but very little direct information about them exists. None has been studied by spacecraft yet. They could be the parent bodies of some volatile-rich meteorites, and there may be an evolutionary connection between them and some asteroids. For example, it has been suggested that some Apollo asteroids are the remnants of extinct short-period comets (Shoemaker and Helin 1977 Kresak 1979).
In summary, three facts about small bodies must be kept in mind: (1) their vast number, (2) their great diversity, and (3) our lack of knowledge concerning them.
The next two decades of solar system exploration should remedy our current lack of information about small bodies. We cannot gain a true understanding of the solar system's evolution by ignoring them. They are of interest not only in their own right, but as the solar system's most abundant projectiles, they have influenced, m some cases probably dramatically, the evolution of the surfaces of the larger planets and satellites.
[137] 7.3. Why Study Small Bodies?
At least four major reasons for studying small bodies in the geologic context can be given:
It could also be argued that another important reason for studying small bodies is that their geologic record may extend further back in time than that preserved on the surfaces of the larger bodies. Also, many small bodies (including satellites) probably are collisional fragments of large bodies and in some instances could provide accessible information on the differentiation of large parent bodies.
7.3.1. Effects of Small Bodies on Larger Objects
Surfaces in the solar system continue to be modified by impacts, and there is abundant evidence that during the first half billion years of the solar system's existence, the surfaces of planets and satellites were influenced dramatically by collisions with small bodies. From the geologic point of view, we are interested in the time history of the flux and population (size and composition) of the impacting objects at different distances from the Sun. The early fluxes appear to have had a profound influence on the evolution of the crusts of larger bodies, and subsequent fluxes are important in [168] determining relative chronologies of different surface units (chapter 3). The actual nature of the impacting bodies (whether volatile-rich or volatile-poor) may have played a role in determining the evolution of some atmospheres and perhaps even of subsequent weathering processes. For instance, it has been proposed that a significant fraction of some gases in the atmospheres of the terrestrial planets were brought in by comets.
Some of the important questions to be addressed are:
In the above, the term "flux" should be understood to mean not only total flux of bodies of all sizes (or masses) but also information about the relative fluxes of bodies of various sizes (or masses).
A vigorous program of searching for Apollo, Aten, and Amor asteroids, as well as for comets, can answer the first of these questions. The second and third questions are more difficult, but considerable progress is being made in addressing some aspects of them by theoretical calculations.
A closely related issue involves the orbital evolution of the various classes of impacting objects (origin, lifetime, and eventual fate). For example, how do objects end up in Apollo orbits? How long do they stay? What happens to them?
7.3.2. Unique Surface Features and Processes
Not surprisingly, there are processes that are important on small bodies but impossible to predict from an extrapolation of our terrestrial or lunar experience. In fact, it is sometimes even difficult to predict a priori what form a well-known process will take in the small-body environment. For example, a decade ago, there was a legitimate discussion about whether or not there would be recognizable craters on bodies as small as the satellites of Mars. A more serious debate developed about whether appreciable regoliths would form on such small objects. Although we have now learned....
....the answers to such rudimentary questions, we cannot pretend to fully understand the process of cratering and regolith formation on small bodies (Cintala et al., 1978; Housen and Wilkening, 1982). For example, we have no convincing explanation for the gross y different appearance of the surfaces of Phobos and Deimos. Why is it that the surface of the smaller Deimos appears to have retained considerably more regolith than that of the larger Phobos?
[140] Our very limited experience in exploring small bodies has already confirmed that unique and unexpected surface features and processes come into play. No one anticipated the existence of grooves on Phobos, yet this type of feature may well be a common one on many small bodies (Thomas and Veverka, 1979). There is every reason to expect that additional, important surface features and processes will be discovered as our exploration of small bodies proceeds, especially in the cases of small icy satellites and the nuclei of comets.
7.3.3. Small Bodies as Natural Laboratories
Due to their great diversity in size and composition, small bodies provide ideal testing grounds for studying various processes especially those involving cratering. In principle, one can find small....
[141] ....bodies of similar surface gravity but drastically different surface composition (rock versus ice), or bodies of similar composition but very different surface gravity, to test the importance of such variables on crater morphology, ejecta patterns, etc. Much could be learned by comparing surface features and regolith characteristics on three small asteroids of similar surface gravity but of different composition (carbonaceous, stony, or metallic). As a next step, one could investigate the effects of rotation rate on regolith characteristics by comparing two asteroids that are identical in all bulk characteristics except their spin rates. Full exploitation of such possibilities would require an aggressive program of future solar system exploration.
7.3.4. Evolution and Interrelationship
There is ample evidence that some small bodies have had complicated evolutionary histories that involved processes of high interest to planetary geologists. The meteorite record proves that some parent bodies experienced internal differentiation, aqueous metamorphism, and even the eruption of lava onto their surfaces (Dodd, 1981). In many cases, very mature and very complex regoliths were developed (Housen and Wilkening, 1982). Understanding the geologic evolution of such interesting bodies is not only worthy in its own right, but would improve our understanding of the possible interrelationships among small bodies and between the small bodies and larger planets. First, there are questions of the following type to be considered: what styles of eruption and what types of volcanic constructs would one expect on a body as small as Vesta? Or, what kinds of structure control the local emission of gases from a comet nucleus? Second, there are the interrelationship questions; for example, is it geologically reasonable that a comet nucleus can evolve into something like an Apollo asteroid or that some volatile-rich carbonaceous chondrites could come from comets? Unfortunately, in many cases we still lack key observational data to address such important questions meaningfully.
7.4. Summary
The small bodies of the solar system are of great intrinsic geologic interest that goes beyond their original role as building blocks of planets and their subsequent role as projectiles. They are characterized by vast numbers and by their diversity.
[142] So far, their geologic study has been hampered by a lack of first-hand information of the sort that can be obtained only by direct spacecraft exploration. Even after Viking and Voyager, our inventory of small objects about which enough is known to carry out detailed geological investigations is very meager. It is restricted to a few icy satellites of Saturn and to the two rocky moons of Mars. We have yet to carry out a geologic reconnaissance of an asteroid or a comet nucleus. Although our accumulated knowledge may be adequate to guess what asteroid surfaces may be like in a general way, we really know next to nothing about comet nuclei. Thus, a first-order requirement for progress in our understanding of small bodies is the exploration of at least one asteroid and one comet nucleus during the coming decade. Some important questions, however, can be addressed only by studying a variety of objects.
In the meantime, it is important to continue the ongoing active programs of Earth-based observations of small bodies as well as related laboratory and theoretical investigations. It is especially crucial to continue monitoring the neighborhood of Earth's orbit for small comets and asteroids, since there is no other way of obtaining adequate statistics on the population of such objects.
In terms of data analysis and interpretation, there are enough unresolved questions concerning the small satellites of Mars and of the outer planets to justify a healthy program of analysis of Viking and Voyager data in these areas. For example, the Viking IRTM * measurements of Phobos and Deimos must be fully correlated with imaging data to gain information on regolith characteristics. We must also develop techniques for mapping irregular satellites and making accurate measurements of their topography and volume. We should make a special effort to apply the many lessons we have learned from comparative planetology during the past two decades to considerations of surface and near-surface processes on small bodies. Such extrapolations from our experience with larger bodies will have to be done judiciously, but the effort should prove beneficial to our general understanding of the solar system.
*Infrared Thermal Mapper.

Question: if the material of the valve is set what temperature does the injection of a comet happen

மிகக் குறைவாக

Known comets have been estimated to have an average density of . if the material of the valve is set very low, the injection of the comet is set in a number of modes without the coat.

if the material of the valve is set what temperature does the injection of a comet happen

Question: what has been estimated to have an average density of

what has been estimated to have an average density of

Question: what causes the injection of a comet without the coat

the material of the valve is set very low

வால்வெள்ளிகளின் பொருண்மை மிகக் குறைவாக

the material of the valve is set very low

what causes the injection of a comet without the coat

Question: what happens to the material of the valve if it is set low

மிகக் குறைவாக

what happens to the material of the valve if it is set low

Question: the injection of a comet is set in a number of modes without what

the injection of a comet is set in a number of modes without what

Known comets have been estimated to have an average density of . if the material of the valve is set very low , the injection of the comet is set in a number of modes without the coat .

Known comets have been estimated to have an average density of . வால்வெள்ளிகளின் பொருண்மை மிகக் குறைவாக அமைவதால், தம்முள் ஈர்ப்பால் கோளமாக ஒடுங்காமல் பல வடிவங்களில் அமைகின்றன.

Known comets have been estimated to have an average density of . வால்வெள்ளிகளின் பொருண்மை மிகக் குறைவாக அமைவதால், தம்முள் ஈர்ப்பால் கோளமாக ஒடுங்காமல் பல வடிவங்களில் அமைகின்றன.

Known comets have been estimated to have an average density of . if the material of the valve is set very low, the injection of the comet is set in a number of modes without the coat.

Known comets have been estimated to have an average density of . if the material of the valve is set very low, the injection of the comet is set in a number of modes without the coat.

Thus, it is clear that the results of the test of the playoffs, 67B/Saturmouth-Cherasimeno Valve, have confirmed that there is no expectancy. Therefore, it is clear that the expectancy is not included in the creation of the start-up of the playoffs.

விண்கலங்களின்

கெராசிமென்கோ

வால்வெள்ளியில்

காந்தப்புலம்

உறுதிப்படுத்தியுள்ளன

வான்பொருள்களின்

உருவாக்கத்தில்

காந்தவிசைகள்

Rosetta and Philae find comet not magnetised
Measurements made by Rosetta and Philae during the probe’s multiple landings on Comet 67P/Churyumov-Gerasimenko show that the comet’s nucleus is not magnetised.
Studying the properties of a comet can provide clues to the role that magnetic fields played in the formation of Solar System bodies almost 4.6 billion years ago. The infant Solar System was once nothing more than a swirling disc of gas and dust but, within a few million years, the Sun burst into life in the centre of this turbulent disc, with the leftover material going into forming the asteroids, comets, moons and planets.
The dust contained an appreciable fraction of iron, some of it in the form of magnetite. Indeed, millimetre-sized grains of magnetic materials have been found in meteorites, indicating their presence in the early Solar System.
This leads scientists to believe that magnetic fields threading through the proto-planetary disc could have played an important role in moving material around as it started to clump together to form larger bodies.
But it remains unclear as to how crucial magnetic fields were later on in this accretion process, as the building blocks grew to centimetres, metres and then tens of metres across, before gravity started to dominate when they grew to hundreds of metres and kilometres in scale.
Some theories concerning the aggregation of magnetic and non-magnetic dust particles show that the resulting bigger objects could also remain magnetised, allowing them to also be influenced by the magnetic fields of the proto-planetary disc.
Because comets contain some of the most pristine materials in the Solar System, they offer a natural laboratory for investigating whether or not these larger chunks could have remained magnetised.
However, detecting the magnetic field of comets has proven difficult in previous missions, which have typically made rapid flybys, relatively far from comet nuclei.
It has taken the proximity of ESA’s Rosetta orbiter to Comet 67P/Churyumov-Gerasimenko, and the measurements made much closer to and at the surface by its lander Philae, to provide the first detailed investigation of the magnetic properties of a comet nucleus.
Philae’s magnetic field measuring instrument is the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP), while Rosetta carries a magnetometer as part of the Rosetta Plasma Consortium suite of sensors (RPC-MAG).
Changes in the magnetic field surrounding Rosetta allowed RPC-MAG to detect the moment when Philae was deployed in the morning of 12 November 2014.
Then, by sensing periodic variations in the measured external magnetic field and motions in its boom arm, ROMAP was able to detect the touchdown events and determine the orientation of Philae over the following hours. Combined with information from the CONSERT experiment that provided an estimate of the final landing site location, timing information, images from Rosetta’s OSIRIS camera, assumptions about the gravity of the comet, and measurements of its shape, it was possible to determine Philae’s trajectory.
The mission teams soon discovered that Philae not only touched down once at Agilkia, but also came into contact with the comet’s surface four times in fact – including a grazing collision with a surface feature that sent it tumbling towards the final touchdown point at Abydos.
This complex trajectory turned out to be scientifically beneficial to the ROMAP team.
“The unplanned flight across the surface actually meant we could collect precise magnetic field measurements with Philae at the four points we made contact with, and at a range of heights above the surface,” says Hans-Ulrich Auster, co-principal investigator of ROMAP and lead author of the results published in the journal Science and presented at the European Geosciences Union General Assembly in Vienna, Austria, today.
The multiple descents and ascents meant that the team could compare measurements made on the inward and outward journeys to and from each contact point, and as it flew across the surface.
ROMAP measured a magnetic field during these sequences, but found that its strength did not depend on the height or location of Philae above the surface. This is not consistent with the nucleus itself being responsible for that field.
“If the surface was magnetised, we would have expected to see a clear increase in the magnetic field readings as we got closer and closer to the surface,” explains Hans-Ulrich. “But this was not the case at any of the locations we visited, so we conclude that Comet 67P/Churyumov-Gerasimenko is a remarkably non-magnetic object.”
Instead, the magnetic field that was measured was consistent with an external one, namely the influence of the solar wind interplanetary magnetic field near the comet nucleus. This conclusion is confirmed by the fact that variations in the field that were measured by Philae closely agree with those seen at the same time by Rosetta.
“During Philae’s landing, Rosetta was about 17 km above the surface, and we could provide complementary magnetic field readings that rule out any local magnetic anomalies in the comet’s surface materials,” says Karl-Heinz Glassmeier, principal investigator of RPC-MAG on board the orbiter and a co-author of the Science paper.
If large chunks of material on the surface of 67P/Churyumov-Gerasimenko were magnetised, ROMAP would have recorded additional variations in its signal as Philae flew over them.
“If any material is magnetised, it must be on a scale of less than one metre, below the spatial resolution of our measurements. And if Comet 67P/Churyumov-Gerasimenko is representative of all cometary nuclei, then we suggest that magnetic forces are unlikely to have played a role in the accumulation of planetary building blocks greater than one metre in size,” concludes Hans-Ulrich.
“It’s great to see the complementary nature of Rosetta and Philae’s measurements, working together to answer this simple, but important ‘yes-no’ question as to whether the comet is magnetised,” says Matt Taylor, ESA’s Rosetta project scientist.
Notes for Editors
“The non-magnetic nucleus of Comet 67P/Churyumov-Gerasimenko,” by H.-U. Auster et al. is published in Science Express on 14 April.
The results were also presented on 14 April at the European Geosciences Union (EGU) General Assembly 2015 in Vienna, Austria, during a dedicated Rosetta mission press briefing.
The data were collected by the Rosetta Lander Magnetometer and Plasma Monitor (ROMAP) on board Philae and the Rosetta Plasma Consortium fluxgate magnetometer (RPC-MAG) on board Rosetta.
Overall, the data show that the comet has an upper magnetic field magnitude of less than 2 nT at the cometary surface at multiple locations, with a specific magnetic moment of < 3.1 x 10–5 Am2/kg, less than known values for lunar material and meteorites measured on Earth.
About ROMAP
ROMAP is the Rosetta Lander Magnetometer and Plasma Monitor. The contributing institutions to ROMAP are: Institut für Geophysik und Extraterrestrische Physik, Technische Universität Braunschweig, Germany; Max-Planck Institut für Sonnensystemforschung, Göttingen, Germany; Hungarian Academy of Sciences Centre for Energy Research, Hungary; and Space Research Institute Graz, Austria. The co-principal investigators are Hans-Ulrich Auster (Technische Universität, Braunschweig) and István Apáthy, KFKI, Budapest, Hungary.
About RPC-MAG
RPC-MAG one of six instruments comprising the Rosetta Plasma Consortium. The fluxgate magnetometer (RPC-MAG) is led by Karl-Heinz Glassmeier, Technische Universität, Braunschweig, Germany.
About Rosetta
Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta’s Philae lander was provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta is the first mission in history to rendezvous with a comet. It is escorting the comet as they orbit the Sun together. Philae landed on the comet on 12 November 2014. Comets are time capsules containing primitive material left over from the epoch when the Sun and its planets formed. By studying the gas, dust and structure of the nucleus and organic materials associated with the comet, via both remote and in situ observations, the Rosetta mission should become the key to unlocking the history and evolution of our Solar System.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Hans-Ulrich Auster
ROMAP principal investigator
Technische Universität, Braunschweig
Email: uli.auster@tu-bs.de
Karl-Heinz Glassmeier
RPC-MAG principal investigator
Technische Universität, Braunschweig
Email: kh.glassmeier@tu-bs.de
Matt Taylor
ESA Rosetta project scientist
Email: matthew.taylor@esa.int

Question: what is the name of the valve in the playoffs

67பி / சூர்யமோவ்- கெராசிமென்கோ வால்வெள்ளியில்

what is the name of the valve in the playoffs

Question: what is the expectancy of the playoffs

காந்தப்புலம் ஏதும் இல்லையென

Question: what is not included in the start of the playoffs

காந்தப்புலம்

what is not included in the start of the playoffs

Question: what is the name of the valve that tests for life expectancy

சூர்யமோவ்- கெராசிமென்கோ வால்வெள்ளியில்

what is the name of the valve that tests for life expectancy

Question: what is the expectancy for the playoffs

Question: what has happened to the expectancy of the playoffs

காந்தப்புலம் ஏதும் இல்லையென உறுதிப்படுத்தியுள்ளன

what has happened to the expectancy of the playoffs

Thus , it is clear that the results of the test of the playoffs , 67B / Saturmouth - Cherasimeno Valve , have confirmed that there is no expectancy . Therefore , it is clear that the expectancy is not included in the creation of the start - up of the playoffs .

1:6.25 and the shadows of the shadows]

* 0.62 g/k/cm3 is obtained with 7.9E+13 cc material using the label . 19b

1: 6.25 கிமீ கோளப் பருமனையும்]]

* 0.62 g/ கி/செமீ3 அடர்த்தியையும் பயன்படுத்த 7.9E+13 கிகி பொருண்மை கிடைக்கிறது . 19பி

1:6.25 and the shadows of the shadows] * 0.62 g/k/cm3 is obtained with 7.9E+13 cc material using the label . 19b /PORELY: 8x4x4 km of hydraulic frame * 0.3 k/cm3 indication is available with 2.0E+13 k/m material. 81B/m material: 5.5x4.0x3.38x4x4mm of hydraulic frame * 0.6 k/cm3 indication is available with 2.28E+13 k/m material.Refs are available with 15 × 8 × 8 0.6 3 k/m material 1 7.6 × 4.9 0.62 7.9 19B/PORELY 8 × 4 × 4 0.3 2.0 81B/m material 5.5 × 4.0 × 3.3 0.6 67 2.3 B/m/m/m/m/m/m/m.

* 0.62 g/k/cm3 is obtained with 7.9E+13 cc material using the label . 19b

And the name of the wicked is the name of the wicked, and the name of the wicked is the name of the wicked.

15×8×8 km of waterproof* 0.6 k/cm3 with the use of the waterproof (m=d*v), 3.02E+14 waterproof is obtained.

The Numbers.

வால்வெள்ளிகளின்

அளவுகள்(கிமீ

பொருண்மை(கிகி)ஆலே

குத்தூண்அடர்த்தியையும்

Question: what does m=d*v stand for

And the name of the wicked is the name of the wicked, and the name of the wicked is the name of the wicked.

15×8×8 km of waterproof* 0.6 k/cm3 with the use of the waterproof (m=d*v), 3.02E+14 waterproof is obtained.

The Numbers.

Question: what is the name of the wicked

வால்வெள்ளிகளின் இயல்புகள் பெயர்

The Numbers.

Question: how much waterproof water can be obtained with the use of waterproof

The Numbers.

how much waterproof water can be obtained with the use of waterproof

Question: what is the waterproof rating for 15×8×8 km

The Numbers.

what is the waterproof rating for 15×8×8 km

Question: what waterproof rating is obtained with the use of the waterproof

The Numbers.

what waterproof rating is obtained with the use of the waterproof

Question: what is the name of the book in which the wicked are referred to

The Numbers.

what is the name of the book in which the wicked are referred to

And the name of the wicked is the name of the wicked , and the name of the wicked is the name of the wicked .

15×8×8 km of waterproof * 0.6 k / cm3 with the use of the waterproof ( m = d*v ) , 3.02E+14 waterproof is obtained .

+சில வால்வெள்ளிகளின் இயல்புகள் பெயர் அளவுகள்(கிமீ) அடர்த்தி(கி/செமீ3) பொருண்மை(கிகி)ஆலே:

15×8×8 கிமீ நீள்வட்டப் பருமனையும்* 0.6 கி/செமீ3 கரட்டுக் குத்தூண்அடர்த்தியையும் பயன்படுத்த (m=d*v), 3.02E+14 கிகி பொருண்மை கிடைக்கிறது.

And the name of the wicked is the name of the wicked, and the name of the wicked is the name of the wicked. 15×8×8 km of waterproof* 0.6 k/cm3 with the use of the waterproof (m=d*v), 3.02E+14 waterproof is obtained. The Numbers.

And the name of the wicked is the name of the wicked, and the name of the wicked is the name of the wicked.

15×8×8 km of waterproof* 0.6 k/cm3 with the use of the waterproof (m=d*v), 3.02E+14 waterproof is obtained.

The Numbers.

The Numbers.

வால்வெள்ளிகளின்

அளவுகள்(கிமீ

பொருண்மை(கிகி)ஆலே

குத்தூண்அடர்த்தியையும்

Summary of properties of Comet 67P/Churyumov–Gerasimenko, as determined by Rosetta’s instruments during the first few months of its comet encounter. The full range of values are presented and discussed in a series of papers published in the 23 January 2015 issue of the journal Science.
More information: Getting to know Rosetta’s comet
Credits for individual results:
Shape model, rotation properties, volume and porosity: OSIRIS
Mass: RSI
Density: RSI/OSIRIS
Dust/Gas ratio: GIADA, MIRO and ROSINA
D/H ratio: ROSINA
Surface temperature: VIRTIS
Subsurface temperature and water vapour production rate: MIRO
Albedo: OSIRIS and VIRTIS
Comet images: NavCam

Question: what is 3.02e+14

Question: how much waterproof water can be obtained with the use of the waterproof

how much waterproof water can be obtained with the use of the waterproof

Question: what is the waterproof rating of the waterproof system

what is the waterproof rating of the waterproof system

The Numbers.

The Numbers.
1:6.25 and the shadows of the shadows]

Rosetta is equipped with a range of instruments to analyse comet 67P/Churyumov-Gerasimenko, but the spacecraft itself can also be used to determine properties of the comet.
As the spacecraft passes close to comet 67P/C-G, it is pulled slightly off course by the comet’s gravity, resulting in tiny changes to the spacecraft’s velocity. These small deviations are recorded in the spacecraft’s radio signals as they are beamed back to Earth, and can subsequently be translated into measurements of the mass and density structure of the comet. The measurements can also be used to refine the details of the comet’s orbit along its trajectory around the Sun.
For the Rosetta mission, this task comes under the umbrella of the Radio Science Investigation (RSI). Using 80 hours worth of tracking data between 6 August, since arriving at the comet, and up to 9 August, the RSI team made a first estimate of the comet’s mass as approximately 1×10^13 kg +/-10%, or about 10 trillion kilograms.
The team caution that there is still work to do with analysing errors on the value, not to mention refining the value as the spacecraft gets closer in the coming weeks. Indeed, these early measurements were made from a distance of approximately 100 km; the spacecraft is now en route to a distance of 50 km.
At the same time, in order to be able to navigate the spacecraft close to the comet, ESA’s flight dynamics and operations teams have also independently determined the mass and gravity parameters. These values fall within the same range as those derived by the RSI team.
The values of both teams are constantly being refined as Rosetta moves ever closer to the comet. In time, once accurate dimensions of the comet have also been determined, the comet’s density will be revealed, and assumptions regarding the comet’s interior can be made.
Discussion: 38 comments
Presumably a volume estimate has already been made, then a density calculation could easily be made. The question then becomes, do the different lobes have different densities?
Since the comet rotation pole is pointing roughly toward the sun, and Rosetta has also thus far been mostly in that direction relative to the comet, there probably isn’t enough data about the shape of the dark side of the comet to get a strong estimate of its volume yet.
Seen the videos of rotation and the position of the rotation axis i can only say that the density is uniform within this kind of measure accuracy at least better the +/- 30%. Make a model of it and check. Use clay and stick an axis through it the way it is in the animations.
The mass is 10.5 Giga ton plus minus 1% and its volume is 21 kubical kilometre making its density to be halve of water.
It rotates in 14 hours and 24 minutes around its axis.
Since the mass is Mt. Everest is about 3×10^15 kg and this comet is a bit smaller in size with 1×10^13 kg of mass, I think it’s safe to say we observing a dry rock rather than a dirty snowball.
Interesting. This mass estimate is about 3 times the initial ‘guess’ of 3.2 X 10^12, mentioned in this earlier post https://blogs.esa.int/rosetta/2014/07/23/last-of-the-fatties/. The shape is better known now, but most of the difference must be in the density – much more solid ice (or rocks?) and less empty vacuum that was thought.
Will the larger mass be helpful for the
mission, in particular for landing Philae?
If the mass were known beforehand, yes. As the lander had been designed for the smaller comet Wirtanen, no.
Not if the cometary nucleus is a rock rather than snow or ice as it is assumed to be.
If the mass is three times the previous estimate, how will this affect the orbital period at 10 and 30 KM?
With no scale for the images at hand but the approximate diameter of 4 km of the comet I started a wild estimate: assuming that the comet consists of two spheres and assuming that ohe might have a diameter of 2.5km and the other one of 1.5km I end up with a volume of 10^10 m^3. From these figure one arrives at a density of 1000kg/m^3, i.e. close to the density of ice? What do you think?
The density of ice is a bit less than 1g/cm^3, your value of 1000kg/cm^3 is 10^6 more dense than ice… but I’m not saying you’re wrong.
That was exactly my estimate 10 minutes ago.
If the earlier estimate of 3.14E12 kg was based on the much larger volume (3D model after Hubble pics), the assumed density was close to only 100 kg/m3. Was it a joke or a miscalculation?
Such a low density? (300kg/cubic meter)
Even a pile of course aggregate used as the base of road construction would have a far higher density than this, even though the pile would be full of air gaps.
Are there any thoughts as to how the structure of the comet could be so full of holes, it should look like a sponge.
When we look at large eroded areas like the striated side of the head, there is no clue to such a porous structure.
Its also difficult to imagine it being hollow, the erosion at the neck has been so extensive, it surely, by now, would have broken through to reveal a hollow core.
Also if the comet is built from interstellar dust, that is expected to be very fine, then you would expect it to pack very densely.
Baffled by these results ??
I think we have to stop making assumptions about comets being “pristine”, “primeval”, “icy”, “rubble piles”, “fragile”. First hand evidence shows a complex, evolved structure. Not only do we have to explain the low density despite a contiguous outer layer, there is also the discrete jets and the non-pristine compounds discovered in previous missions. I am thinking “chambers”, under the surface where pressure builds up, powering jets.
The new estimated density is higher than expected, not lower. Uncompacted snow can be well under 100 kg/m^3, see https://www.sciencelearn.org.nz/Contexts/Icy-Ecosystems/Looking-closer/Snow-and-ice-density and with no gravity or freeze/tham cycle to compact it, snow + dust at an average density of about 100 kg/m^3 was the guess. What Rosetta has found is either much dirtier (rock at density 3000-5000 vs ice at 1000) or much more compacted than expected.
The assumption of no freeze/thaw cycles in comets has taken a battering from recent scientific discoveries. The discovery of a CAIs from stardust indicate the likelihood of melt zones early in the comet’s history. The discovery of cubanite also indicates that there was liquid water processing inside comets for the comet in question. The question is why a comet wouldn’t collapse down in on itself when a lot of its volatiles melt, evaporate and sublimate, increasing its density to close to that of ice.
Suppose there are a lot of organic molecules, so that the surface has a much more squishy composition (I am thinking of something like tar). Would that match the density better? Would that explain sharp crater rims?
An ice block should be about 1 g/cm3, so your guess is not far from expectations, but surely the team has a much better estimate of the total volume, better than the mass, by now.
It would be nice if they put out a first density measure, even at a 20% error level.
How do you mesure theese tiny changes to the spacecraft’s velocity ? what are your FIX Points out there, that will help you determine this pulling/pushing Force ? (pushing, in sense of, how gravity maybe is a pushing from Outside force between 2 Bodies)
thx.
The main two measurement types are the doppler signal (the shift in radio frequency when Rosetta talks with ground stations on Earth, caused by relative motion) and optical data (identifying landmarks in pictures of the comet).
Even though any individual measurement could be fairly incorrect, combining enough of them over a time span of several days makes it possible to determine the forces acting on Rosetta with good accuracy.
I agree density the of 300kgs per cu meter is higher than first projected.
However this and all the other comets we have seen look like solid rocks not icy balls, in which case this s.g. would look rather low.
The comet pictures we have seen from this and other projects look like meteorites and as far as I know, we would not expect the debris of meteorites to be floating on the sea after coming to earth.
I have thought it iwould be heavier.
If the mass is 1×10^13 kg, then at 50 km distance, the orbiting period shall be 31.5 days and orbiting velocity 0.12 ms-1.
At 30 km, period and velocity shall be 14.6 days and 0.15 ms-1.
So measuring orbit time shall be enough to estimate the mass.
The point is that it has not been orbiting yet, but “triangulating”.
But amazing. Take care.
About as wrong as anyone could be Ross. If the mass of the comet is less than 1% of the mass of Everest, then the nucleus density comes out a very low number,, not rocky at all. Why don’t you wait until the scientists tell you the right answer.
What is the volume of 67P? How was it determined since its odd shape was a surprise?
Is their a 3d model of it in some widely known format such as Googl’s SketchUp (.skp) or such?
I know I could work with the density given by the newly discovered mass but it leads me to wonder whether the volume is also up to date.
About the extra mass I would suggest the possibility that there are two heavy nuclear reactors each inside both dumbbells? Then the lander could have a rerious problem?
Thanks once again. It is not ‘in orbit’ yet but I think you can give a reliable estimate of the density now (do !). Wikipedia among others earlier gave about 100 kg/m^3 (a bit, well, very low). I suppose it is now like known comets, 500 kg/m^3 or a tad more.
You must have better numbers ! Groeten, Henk Smid
https://www.engineeringtoolbox.com/mineral-density-d_1555.html
This is a mineral density table for earth minerals. Compared to any estimate of the comet material density you soon realise that the comet is pretty fluffy. Its material actually floats on water better the most woods does. Its consistence i speculate to be like saw dust and absolutely not rocklike at all.
This is my guess.
The material is most likely sublimated ice of water mixed with ice of hydrocarbons and ice of carbon-oxides mixed with mineral dust. The nano- and micro-particles compressed during eons in very low gravity to a real softie. There are a few heavy gasses in situ but not much of it. Any liquids are rare as it is in vacuum with very low atmospheric pressure an almost vacuum as well. I estimate the core temperature to about 70 K so some gases are liquified and soaked up in its interior but so rare it is hardly making it wet. Whatever we will learn from it will be a surprise even for the scientist as they too have not much of a clue yet.
Comet 67P and Schoemaker Levy 9.
What can the Schoemaker Levy 9 Comet destruction into 24 point sources, tell us about Comets in relation with the multi gravitating dark matter point source proposal for Comet 67P C-G by Quantum FFF Theory? Conclusion: Comets are aggregations of multiple dark matter point sources coined new paradigm interference Black holes. The different sizes of Comets (below) is an indication that Comets seem to grow by merging with other comets.
see:https://www.flickr.com/photos/93308747@N05/14933737128/in/photostream
https://www.flickr.com/photos/93308747@N05/?details=1
Today’s blog post (https://blogs.esa.int/rosetta/2014/09/24/rosettas-night-time-excursion-and-a-go-for-20-km/) gives some details about Rosetta’s recent orbit: 28km x 29km at a period of 13d14h59m. This puts the mass at about ~9.9 x 10^12 kg which nicely fits the initial estimate of 10^13 kg +/-10%.
Do you think that NASA will actually show us an actual picture of the comet? Because I’m getting sick of seeing the same picture they showed last year from comet Ison. So i guess my question should be why is NASA showing us an old picture of comet Ison instead of an actual picture of the comet.
What deviation of radio signal was measured? Was it the doppler shift?
Hello,
I am not a scientist, so this question mail can be pretty embarrassing for me. I am just wondering about terminology such as the use of the word “orbit” in reports, media, etc…
There is said that Rosetta is “orbiting” comet 67P. But can anyone explain how that is possible without serious engine force? Even if the comet is composed by the most dense and heavy materials, it is to small to generate enough gravity for a +1 ton weighting vehicle to stay in a natural orbit.
I assume that we shouldn’t talk about orbiting? Probably Rosetta is just flying side by side? With a few corrections via electric engines?
Stefaan
What is the surface value of g where it landed?
it can orbit, The mass is small compared to the earth, but the distance of about 30km is so much closer than that of a sattellite around earth with more than 7000km.. the force increases with 1/r^2 The orbiting time is about 14d.
Ok

Question: what are the numbers 1:6.25 and

The Numbers.
1:6.25 and the shadows of the shadows]

Question: 1:6.25 and the shadows of the shadows are what

1:6.25 and the shadows of the shadows are what

Question: along with the numbers, what else is mentioned in the numbers

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along with the numbers, what else is mentioned in the numbers

Question: what is 1:6.25

Question: what are the shadows in the numbers

Question: how many shadows are there in the numbers

how many shadows are there in the numbers

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<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997File:Comet P1 McNaught02 - Comet P1 C/2006 P1 (McMt) in Austria 2007

ஆசுத்திரேலியாவில்

விக்டோரியவில்

This NASA Hubble Space Telescope set of images reveals a never-before-seen set of six comet-like tails radiating from a body in the asteroid belt, designated P/2013 P5.
The asteroid was discovered as an unusually fuzzy-looking object with the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey telescope in Hawaii. The multiple tails were discovered in Hubble images taken on Sept. 10, 2013. When Hubble returned to the asteroid on Sept. 23, the asteroid's appearance had totally changed. It looked as if the entire structure had swung around.
One interpretation is that the asteroid's rotation rate has been increased to the point where dust is falling off the surface and escaping into space where the pressure of sunlight sweeps out fingerlike tails. According to this theory, the asteroid's spin has been accelerated by the gentle push of sunlight. The object, estimated to be no more than 1,400 feet across, has ejected dust for at least five months, based on analysis of the tail structure.
These visible-light, false-color images were taken with Hubble's Wide Field Camera 3.
Object Name: P/2013 P5
Image Type: Astronomical/Annotated
Credit: NASA, ESA, and D. Jewitt (UCLA)
To access available information and downloadable versions of images in this news release, click on any of the images below:

Question: in which country was the comet p1 mcmt manufactured

ஆசுத்திரேலியாவில்

<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997File:Comet P1 McNaught02 - Comet P1 C/2006 P1 (McMt) in Austria 2007

in which country was the comet p1 mcmt manufactured

Question: what company manufactured the Comet p1 c/2006

what company manufactured the Comet p1 c/2006

Question: what is the gallery mode of a comet called

heights=150px > File : Comet - Hale - Bopp-29 - 03 - 1997 hires 1997இல்ஏல் - பாப் வால்வெள்ளி

what is the gallery mode of a comet called

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Question: what mode is used to display packed heights

mode = packed heights=150px > File : Comet - Hale - Bopp-29 - 03 - 1997 hires 1997இல்ஏல் - பாப் வால்வெள்ளி File : Comet P1 McNaught02 - வால்வெள்ளி

what mode is used to display packed heights

<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997இல்ஏல்-பாப் வால்வெள்ளி File:Comet P1 McNaught02 - வால்வெள்ளி C/2006 P1 (மெக்நாட்) ஆசுத்திரேலியாவில் 2007இல் விக்டோரியவில் எடுத்தது.

<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997இல்ஏல்-பாப் வால்வெள்ளி File:Comet P1 McNaught02 - வால்வெள்ளி C/2006 P1 (மெக்நாட்) ஆசுத்திரேலியாவில் 2007இல் விக்டோரியவில் எடுத்தது.

<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997File:Comet P1 McNaught02 - Comet P1 C/2006 P1 (McMt) in Austria 2007

<gallery mode=packed heights=150px> File:Comet-Hale-Bopp-29-03-1997 hires 1997File:Comet P1 McNaught02 - Comet P1 C/2006 P1 (McMt) in Austria 2007

Question: what is the scientific name for a comet

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what are the objects in our solar system known for

Question: where is the Catalogue of the solar system located

where is the Catalogue of the solar system located

Question: what is the name for the evolutionary process of comets and asteroids

what is the name for the evolutionary process of comets and asteroids

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who is responsible for cataloging comets in our solar system

Question: how to make a model of a comet

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what is the purpose of the periodic table

Comets Page at NASA 's Solar System Exploration International Comet Quarterly How to Make a Model of a Comet audio slideshow – National High Magnetic Field Laboratory Catalogue of the Solar System Small Bodies Orbital Evolution Information about comets and asteroids