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Astrobiology: Enter the Seager Equation

An essay of mine called Distant Ruins is now available from Aeon Magazine, looking at a field that is increasingly becoming known as ‘interstellar archaeology.’ Rather than looking for radio or optical signals flagging an extraterrestrial culture, some scientists have asked whether a sufficiently advanced civilization might not have left evidence of its existence in the form of huge engineering projects, mining asteroids or breaking up entire planets to build Dyson spheres. Or perhaps so-called ‘blue straggler’ stars are evidence of a culture tinkering with its own sun.

I speculate in Aeon that what we may someday detect in our rapidly growing astronomical databases is evidence not of living but long-vanished cultures, whose mega-engineering may stand as enigmatic evidence of beings that died before our Sun was born. We don’t, after all, know how long technological civilizations live, and there is no reason to think them immortal.

All of this plays into today’s post because one of the key elements of the Drake Equation is the term L, which stands for the lifetime of a technological civilization. On this matter we simply have no knowledge, other than to say that our own culture has managed to survive with technology until now. Do civilizations inevitably destroy themselves at some point through misuse of their tools, and is this the ‘Great Filter’ that a culture has to make it through to reach maturity?

An Alternative to Drake


We can ponder these issues as the various forms of SETI proceed, but we should remember that the hunt for biological — not necessarily technological — markers is ongoing. At MIT, Sara Seager is offering a new take on the Drake Equation that opts to look not at intelligent life but at the presence of life itself. It’s a smart decision because we’re coming up on an era when we’ll be able to probe the atmospheres of potentially habitable planets around small M-class dwarf stars. Not only is the TESS (Transiting Exoplanet Survey Satellite) mission in the works, but we also have the James Webb Space Telescope. If TESS can find candidate planets around stars, JWST can study them to learn whether the biosignature gases that mark life are there.

Image: MIT exoplanet hunter Sara Seager.

Seager’s equation is a sharp break from Drake’s, and I’ll pull it right out of this Astrobiology Magazine interview, to which I refer you for more background::



N = the number of planets with detectable signs of life
N* = the number of stars observed
FQ = the fraction of stars that are quiet
FO = the fraction of those planets that can be observed
FL = the fraction that have life
FS = the fraction on which life produces a detectable signature gas

What’s being left out is immediately obvious when compared with the famous Drake approach. Here’s Drake’s original formulation:

N = R* fp ne fl fi fc L


N = The number of communicative civilizations
ne = The number of Earth-like worlds per planetary system
fi = The fraction of life sites where intelligence develops
L = The “lifetime” of communicating civilizations

You can see that Seager’s approach focuses solely on biosignature gases, which we are usefully able to study because the atmosphere of a planet transiting its host star will absorb some of the starlight. So we’re looking for photons of starlight shining through the atmosphere of a planet, and we’re also looking for stars quiet enough that flare activity and other disruptions don’t mask the data we need to gather from the transiting planet. Some figures in Seager’s equation can be calculated: The fraction of M-dwarfs with planets in the habitable zone, based on Kepler statistics, is roughly 0.15 for quiet stars. Other terms are, as Seager says, just guesses, including the fraction that have life and the fraction that produce a detectable signature gas.


Image: Habitable zone relative to size of star. Credit: Wikimedia Commons.

Much could be said about biosignatures themselves. On the Earth, oxygen, ozone, methane and carbon dioxide are produced biologically, but could also occur naturally in the atmosphere of a planet that was devoid of life. So it’s not so much a single gas but a combination that tells the tale. A biosignature would be the simultaneous presence of these gases in quantities telling us that life must be part of what is keeping them in production. On that score, Seager’s last term — the fraction of planets on which life produces a detectable signature gas — is cunning because it leads to the basic issues that will have to be resolved as we broaden the hunt for life. Says Seager:

I carefully crafted the last term of this equation so one could actually add more information in. Does life produce a detectable signature? Are there systematic effects that rule out some biosignature gases being detected in some planets? Can we not find the signature for technical reasons? We just don’t know how many planets have life that is producing biosignature gases that are detectable by us.

None of this de-emphasizes the current SETI effort, which proceeds with Drake’s Equation very much in mind. But Seager’s new equation is a nice addition to the exoplanet toolkit. After all, we have no idea whether or when a SETI project will pull in evidence of an extraterrestrial civilization. But in Seager’s view, there is at least “a remote shot” that we’ll detect a biosignature within the next ten years. Inferring some kind of life on a distant world isn’t like being handed the password to the Encyclopedia Galactica, but it would tell us that life is not confined to our own world.



Comments on this entry are closed.

  • James D. Stilwell September 11, 2013, 10:43

    This one gets bookmarked too…And about ‘Distant Ruins’….Arthur C. Clarke wrote distant ruins into his ‘The City and the Stars’….Odd how like attracts like….JDS

  • Rob Flores September 11, 2013, 11:30

    I am dubious of the accuracy of predicting life based on atmospheric
    composition. We simply don’t have any idea if the composition and layering
    of our planet’s solid body is typical for it’s size. If we look at venus we find
    great differences (not all caused by the abesence of water) , and from the looks of it’s core composition maybe different, since it has an almost non-existant magnetic field. If place venus at the 1AU from the start of it’s
    formation, are we sure we would get an earth twin?.
    Wishful thinking skews things I am fraid. For a moment there when Titan exploration was analysing its atmosphere, one reseacher annouced that the hydrogen being produced up high was being consumed at the surface
    and that could be a lifeform. There was a talkdown from that point of view,
    as it was felt by others that we did not fully undestand the chemistry of the surface and might explain odd Hydrogen levels. Now imagine this episode happening EACH time we encounter an amospheric anomaly. Worse for
    us we have no way of going there and analysing insitu, like we could on Titan.
    We should still try caterogize these alien atmosphere’s as we have no hard data as to what we might find in 1.25-1.75 RE planets. I do not rule
    that once a large database of these atmosphere’s we migh find that there is a pattern to them. I think if we find one odd signature per 50 or 100 cases
    I think it would indicate life. On the other hand if we find 50 odd signatures
    it might indicate that chemistry is playing a joke on us, by having pathways
    to false-biosignatures we cannot Imagine. The reason I would not believe
    the 50 positive result is Fermi. To me fermi points to a rarity of life.

  • JadeStar September 11, 2013, 11:38

    What strikes me about all this is that unlike radio, Earth has been transmitting bio-signatures for at least 2-3 billion years.

    This puts a lie to those who suggest intelligent aliens would not know the Earth had life because our radio signals are only out to about a 70 light year radius. (With the assumption that the nearest ETI would be much more distant than that).

  • Alex Tolley September 11, 2013, 12:07


    The idea of the HZ as defined by liquid water on the surface may be too narrow if life is not assumed to be just a surface phenomenon, driven by sunlight.
    Having said that, unambiguous biosignatures from even a handful of planets would be very exiting. It might indicate that independent genesis is possible (unlike the Mars/Earth situation). I think that this could be a strong driver to develop more powerful instruments to image such worlds and eventually fast interstellar probes to the nearer ones. As with the wide public interest in Lowell’s Mars that was believed inhabited, so would be the public interest in worlds that were living.

  • Michael Michaud September 11, 2013, 12:47

    Seager has made a useful addition to the debate by proposing an alternate equation.

    Earlier, others had made several suggestions for revising the original Drake equation. Ward and Brownlee introduced new factors affecting the probability of life and intelligence. Papagiannis and Mauldin argued separately that the original equation neglects the factor of time, assuming that all factors are relatively unchanged. Dyson emphasized the effect of interstellar expansion and colonization, which could establish technological civilizations in new locations; Shostak and Barnett acknowledged that one star system could seed others. Viewing added that colonies could establish other colonies. Brin proposed three new factors including the velocity of expansion, the lifetimes of the colonies, and the probability of approach or avoidance.

    After reviewing these ideas in Contact with Alien Civilizations, I added the most mysterious factor of all: motivations and intentions. Sentient beings can make choices about what they should do.

    From what I have seen, the problem is not a lack of ideas, but a lack of evidence. We still don’t know what numbers to insert in the added factors. Only science can fill in the blanks.

    Michael A.G. Michaud

  • FrankH September 11, 2013, 15:20

    The Earth’s bio-signature has changed dramatically over the last 2-3 BY. I’m not sure you can even consider the Earth habitable for many of those eons; at least not by humans. Most humans would not haven been able to survive for long without supplemental oxygen in the late Devonian, when O2 levels were below 15% (as low as 13%).

  • Ron S September 11, 2013, 16:04


    Yes! The Drake equation is simply a means of asking a question. Finding 1,000 other ways of asking the question is perhaps interesting but still worth less than a single datum. We need data, not more questions.

  • Astronist September 11, 2013, 18:46

    Michael Michaud helpfully mentions a number of reconsiderations of the Drake equation which take account of the possibility of interstellar colonisation.

    I find it useful to consider that there are two basic hypotheses here, which we may call the Steady State and the Big Bang hypotheses of civilisations around the Galaxy. The Drake equation is based on the Steady State concept: for a long time in the past, and for a long time to come, civilisations have been and will continue to be coming into existence, persisting for a while and then vanishing again. The locations at which they are found are always the same as those at which they originally evolved.

    Opposing this is the Big Bang concept: for a long time the Galaxy is devoid of intelligent life, but then one civilisation appears and spreads throughout the Galaxy in a relatively brief period of time (on the order of 100 Myr, or 1% of the age of the Galaxy to date). Thereafter, the locations at which intelligent life is found are almost all colonies, and that life is ubiquitous and permanent.

    However, sorry, this is wandering off topic, as Sara Seager is focused on the somewhat different question of just those planets which have surface-dwelling, pre-technological life.

    Oxford, UK

  • Astronist September 11, 2013, 19:00

    Paul: “We don’t, after all, know how long technological civilizations live, and there is no reason to think them immortal.” True. And yet, is this how life has evolved in the past? The pattern from evolution is that each level of biology has given rise to a higher level founded on it: thus prokaryotic cells produced eukaryotic cells produced multicellular life produced technological life. As each new level of complexity appears, the previous level also persists in symbiosis with it. Furthermore, whereas even bacterial life could not originally have hoped to outlive the death of the Earth when the Sun approaches its red giant phase, providing that our civilisation fulfils its potential then those less complex organisms will, along with ourselves, continue to live and prosper long after the death of the Sun.

    The pattern therefore suggests not only that our own kind of life (technological civilisation) will produce some kind of successor at a higher level of complexity, but also that there is no reason for industrial civilisation to die out once it has become properly established. Which, I suggest, is once it has become established at a variety of different points in the Solar System, thus is no longer a monoculture.


  • James D. Stilwell September 11, 2013, 20:09

    Michael Shermer produced his own adjusted Drake Equation and came up with 2.44 civilizations in our galaxy….He must have recently adjusted the number again….the last time I looked, it was 3.25 civilizations in the galaxy…..He’s very serious….See: “Why ET hasn’t called”…..JDS

  • Heath Rezabek September 11, 2013, 21:27

    Biosignature is, in a way, a signal like any other, except that we assume it to be unintentional and predating civilization(s).

    During Starship Congress, at the end of Jim Benford’s session on METI, I raised the possibility of a strategy that would mask detection by other civilizations through deliberate transmission of competing signals to mask any signals transmitted; Jim clarified that this would actually be trivial to do, as the competitor could simply tune a countersignal 180 degrees out of phase with the original signal to achieve the effect.

    I wonder here if we can imagine biomasking signals as plausible options, as well. Nick Nielsen, in his blog entry on the session, noted that if we can conceive of a trivial way to mask signals in the small, then this strategy could be imposed in the large by the first civilization advanced enough to develop The Great Silencer as it were.


    While masking biosignatures would be more complex, we could envision an advanced civilization taking the liberty of at least obfuscating them on a large scale if there were an ethical reason to do so. In other words, if an advanced enough civilization determined that independent evolution were a moral or ethical imperative, and were certain enough of the finding, they could impose silence on the perceiving cosmos in order to enforce it.

    All of this is very speculative, but it led to Sonny White joking that we could add another variable to the Drake/RE/Seager equations to stand for “the total number of advanced civilizations to impose masking signals on the local neighborhood’.

  • Digbijoy September 12, 2013, 3:45

    I believe that no matter how much we try, our imagination, understanding, guesses and search for extra-terrestrial life will always be consciously or sub-consciously guided by our understanding of earth-based life, for, we humans have evolved thousands of years co-existing with our earth’s ecology and hence we will always tend to think of life ‘as we know it’ which actually may not likely be the case. As persons of science, we should not rule out something just because our understanding of physics, chemistry and biology doesn’t permit it. We should always be open to skepticism, questions and ‘what if?’ attitudes. Just because earth-based life requires 25 deg celcius at surface, abundant water, complex biological molecules rich in carbon-hydrogen, doesn’t mean we should rule out planets which do not ‘fall’ in to habitable zone or planets which do not satisfy the criteria for sustaining earth-based life-forms. Our understanding of extra-terrestrial life forms is ZERO. We have no data. We are always (mis)guided by our earth-based life’s concepts.

    How can life develop on planets with no complex bio-chemical molecules ? How can life develop on planets with no oxygen and no water ? We don’t know. It may. It may be too bizarre for us to even comprehend ! Just because ‘we’ need water and complex molecules doesn’t mean anything in the cosmic scenario. Imagine 400-500 years back in time, tell Isaac Newton or Galileo that there is something invisible and imperceptible to us surrounding us everywhere which could enable you to see in real time what your friends are doing hundreds of miles away on a screen in a tiny hand-held object (now called mobile phone), and that you could even speak to your friend watching him in that tiny hand-held object. Newton and Galileo would be shocked to their lives ! It’s unimaginable back then.

    Science still has infinite amount of knowledge to unearth and unravel. Let’s not be confined to concepts of carbon-based Oxygen-requiring life forms.

    What if, for instance, intelligent lives elsewhere, due to a completely different set of ‘evolution’ develop not the five senses we humans have ? our five senses – hear, sight, speech, smell and touch – through which we acquire, process, understand, observe, verify everything in the universe, had been biology-and-evolution-dependent. What if extra-terrestrial life-forms have developed different senses of perception, beyond our imagination, two of which for instance, say, hear and smell, overlap with ours, but have four totally different senses which we humans can not imagine no matter what ? There may be phenomena happening in universe around us which our 5 senses can never pick up or verify or observe no matter how advanced our technology is, and such phenomena may not affect the phenomena which are observable by our 5 senses. We would always be in the dark about those un-observable phenomena. Who knows ? Maybe rich physics lies in those phenomena beyond our 5 senses ? This may sound meta-physics and pseudoscience, but who knows ? Who can verify ?
    So what if extra-terrestrials posses different sets of senses and hence perceive the universe and its physics in somewhat different form? The physics they observe/verify is correct just as ours is correct (for us), but both them and us (humans) may discover/understand different subsets of physics in a ‘mega’ set of physical laws. All our attempts to hunt for them, and their attempt (probably) to hunt for us, will be such an irony !!

  • Ronald September 12, 2013, 4:55

    Interesting addition, but what I find the weak aspect of the Seager equation is that, contrary to Drake’s, it is strongly dependent on our (present) technological capabilities (detection) and hence the outcome is not a natural given but a (rapidly) changing value.

    With regard to biosignatures, I would think that a high atmospheric O2 content on a (terrestrial) planet with moderate temperatures (i.e. other than photo- or thermo-dissociation) is highly indicative of life, because of the well-known very reactive nature of O2.
    But having said that, our own atmospheric O2 content was quite low for most of Earth history with life, probably not much above 3%, until long after the Great Oxygenation Event the Earth O2 sinks, particularly the crust, became saturated.
    Question is how well we will be able to detect such a low O2 content. And in fact (primitive) life can even be anaerobic.
    A high O2 content would probably be indicative of complex life.

    But any unambiguous detection of a biosignature would be revolutionary and historic, the discovery of the century, if not the millennium.

    Rob Flores: “Fermi points to a rarity of life”. No, strictly speaking Fermi only point to rarity of technological civilization, everything else is interpretation.

    But I agree with JadeStar, that the Earth has been a shining biosignature beacon for aeons, which does not bode well for Fermi: I am utterly convinced that any advanced civilization in the MW galaxy knows that we (Earth, complex life) are here.

  • David Cummings September 12, 2013, 8:03

    The Drake Equation is based on the technology of radio telescopes and the hunt for ET transmissions. It is still a valid equation as that hunt continues with bigger and better radio telescopes.

    The Seager Equation is based on the recently acquired capability to actually peer into the atmospheres of planets in other systems. This is an incredible development an amazing advance in astronomy and it is natural that a new equation such as this is formulated.

    This is a new question, a question that can only be asked because of technological developments.

    In the future those developments will continue, making new questions and new equations possible.

    I wonder what questions we will be asking when we finally have a robotic telescopic array on the South Pole of the moon.

  • Andrew Palfreyman September 12, 2013, 11:24

    Exoplanets have captured the public imagination, both in our (perhaps surprising) ability to detect them at all, and in their sheer number. The hunt is now on and momentum is building to expand our detection capabilities. We look forward to the processing of the remaining Kepler data, and in three years or so we’ll have TESS and JWST. It’s a Golden Age for astronomy right now in at least this respect. Our grandchildren will know of tens of thousands of exoplanets, and this knowledge will be the real fuel which draws us inexorably outwards.

  • Alex Tolley September 12, 2013, 11:29

    @Heath – but a masking of a biosignature implies technology, which will not apply to pre-technological living planets, i.e. probably almost all of them. (unless civilization[s] has occupied them via colonization).

    Is it really possible t be able to mask every conceivable bio/tech sign yet leave what appears to be a dead/inhospitable planet in view? What if that encourages von Neumann replicators to arrive as there is no “prime directive” preventing them from deconstructing a dead world?

  • Rob Flores September 12, 2013, 11:30

    Digbijoy Wrote:

    Indeed it maybe easier for life to arise in an N2-CO2 world with an abundance of liquid water, in a benign earth type world. But these type
    of worlds seem hard to come because water has such narrow liquid range. If, as the Kepler mission has been hinting , it turns out that planets tend to bunch up close to their primary is a very common solar system arrangement then we probably have some surprises in store on these hot worlds.
    These Hot worlds together with Ice worlds/moons make up the vast majority of our solid body objects in our solar system. Just the vastness
    of the numbers of stars in our galaxy seem to me indicate we will find a surprising number of non carbon life forms, eventually.

  • NS September 12, 2013, 12:38

    As Digbijoy points out, we are indeed constrained by our understanding of Earth life, but at this point in our understanding we just need a place to start looking. Searching for bio-signature analogues of Earth (as it is now or was in the past) is the logical place. As for intelligence/technology, we don’t know at this point whether it inevitably arises in some fraction of planets that have life, or if (as some biologists suspect) it is an evolutionary fluke that is unlikely to occur elsewhere. We need to go beyond SETI searches only.

  • Sedjak September 12, 2013, 13:12

    Recent discoveries point to organics being formed in space much nearer to absolute zero temperatures because of quantum tunneling. This is a revolutionary finding because now we have a mechanism for life to form and thrive in conditions that are commonplace throughout the galaxy. It may be a slow process but one could now imagine an intelligence evolving in a dense nebula or even the atmosphere of a gas giant or Europa’s ice. This ETI may have perception or a nervous system that utilizes quantum tunneling (or even entanglement), along the lines that Digbijoy argues…

    Scientists could also explore biosignatures with funky polarizations of light including corkscrew and “starfish” that have been in the news in recent years. Perhaps an ETI is polluting space with its version of “I Love Lucy” and we wouldn’t even know. Or more on topic, aforementioned Gas Giant ETI might be lasing its communications to its neighbor planets with this kind of light or something even stranger. Let’s look for it.

  • Peter Chapin September 12, 2013, 19:53


    I agree with this also. If nothing else an advanced civilization would have already inspected Earth remotely using telescope technology we are about to possess ourselves. However that doesn’t mean they would come here. If life turns out to be common in the galaxy the fact that Earth has it might make Earth just “another boring planet with life.”

    I’m not sure what this means for Fermi, though. Perhaps they haven’t contacted us because they don’t know we are here and just assume earth is still covered with primordial forests or some such. Meanwhile they communicate among themselves using technology we know nothing about and have no idea how to detect. They certainly wouldn’t be using smoke signals… er radio waves.

  • Ronald September 13, 2013, 4:41

    Rob Flores: “Just the vastness of the numbers of stars in our galaxy seem to me indicate we will find a surprising number of non carbon life forms, eventually”.

    I don’t think so. The galaxy and the universe may be vast, and I am sure, that we will be continuously surprised by the universe as we keep on discovering more and more about it, but the rules of the game don’t change over time and space, i.e. the fundamental laws of physics and chemistry will be the same all over.
    Life is most likely to be based on carbon and (liquid) water, because of its very typical characteristics. E.g. although silicon is extremely common, we find no life based on it. Ammoniak and methane might be used as a transport liquid, but are liquid only at very low temperatures where biochemical processes are very slow.

    If it appears that (by far?) most planetary systems are so-called compact systems and (by far?) most planets are mini-Neptunes and Neptunes and most of those in orbits too close for comfort, i.e. not conducive to (complex) life, then that is the way it is. It will make our own case, and similar ones, extra special, to be sought out and cherished.

    I am an optimist: I do still think that terrestrial planets in the HZ of solartype stars may be reasonably present, even if a small minority, rarity is a very relative concept in the vastness of the universe. And even when we find terrestrial planets that are potentially suitable for life, but not bearing it, we can one day bring it there.

  • Marshall Eubanks September 13, 2013, 10:06


    I think that is correct, as any such civilization is also likely to be billions of years old, plenty of time to generate a list of every planet in the galaxy, inhabited or otherwise. However, if there is no faster-than-light (FTL) travel, then such a civilization is also used to information (about new civilizations, say) taking tens of thousands of years to cross the Galaxy. Taking 10,000 years to get around to talking with new arrivals may just be par for the course (and it would probably help to weed out flashes-in-the-pan).

    From that perspective, Fermi’s observation (AKA “paradox”) may be mostly evidence for the non-existence of FTL travel, and we may have a while to wait.

  • Swage September 13, 2013, 22:02

    Fact is, given our current (decresing, because we move more twoards wire) communication signature, it is subjet to the inverse square law. This means, with detection equipment like ours, we would have a hard time detecting a similar signal within a radius of a lightyear. Even a technology a hundred times as efficient would do not much better because the signal looses exponetially more strength as distance increases and its really hard to distinguish it from the background noise unless in very close vicinity. Radio signals are not obvious, so no 70 lightyear bubble, at least not an very apparent one. This may calm some tempers fearing we got a big pointer drawing every exploitative high tech civlization in the area twoards us. Personally i am more relived because… well… i am not totally conform with a lot that got aired as being a particular positive representative for our race in general.

    Biosignature. Lets do an estimate about the radius. I estimate a five kilometer per second speed for ejecta at least, according to Belbruno’s “Chaotic Exchange of Solid Material between Planetary Systems: Implications for Lithopanspermia”. A lightear is around 10 trillion km. With 5 km per second this equals to ~6500 years travel time for a lightyear. First life on Earth arguabely showed up some 3.6 billion years ago.

    So… our biosignature has a range of aproximately 550 thousand lightyears.

    Depending on how close you are, it will not be an easy task to trace its trajectory. This is furter complicated by the situation of both planets having biosignatures, including the neccesary realization and acceptance that there is an extraterrestrial biosignature. Then its only logical to assume there are more than two worlds seeding the cosmos and this is further complicated by the material possibly seeding (including colonizing) other worlds along its path. In this scenario its near impossible to trace the biosignature to its point of origin.

    Of course… by careful analysis of the signature you may become aware what kind of world you are looking for, but not knowing the conditions on Earth, it will be also very hard to deduce not only where, but also when it came from.

    To be blunt, for these and some other reasons i am personally convinced the Fermi Pardox does not exist. I think its a total delusion and i think it became clear the moment the ISS experiments gave us the results for microbe survival in space, including impact scenarios, hyper-velocity experiments and multiple reports about microorganisms wich have been hibernating for millions of years on Earth only to be revived in the lab. All these results are

    I also want to remind that we have evidence for life in the fossil record of Earth as far as it is intact. Given the odds of a replication system rising by chance, wich certainly must have happened at one point, it strikes me as totally abnormal to see it conquering this planet so early, basically as soon as environmental conditions permited it.

    Indeed i think it points to a very occupied environment of hibernating “biosignature” in this area of the Milky Way, wich also points to the conclusion that a lot of habitable and inhabitated planets MUST be around to produce such a density of terraformers, to the point that those linger around forming star systems, directly infesting planets during the formation process.

    And in this light, especially when it comes to Tipler’s interpretation of the Fermi Paradox, namely the absence of Von Neumann Machines as evidence for the absence of advanced civilizations, i think we are absolutely and utterly mistaken.

    The sun may die but life continues.
    This is no coincidence.

  • Heath Rezabek September 14, 2013, 22:52

    @Alex – Masking of biosignatures seems far more difficult than masking of intentional signals, but then again, if we can conceive of it, the rest is wherewithall. You are right about the risk of encouraging von Neumanns, but even an obfuscating signal could do the trick. Is it possible to wash away steady pulses in a sea of random noise, thus leaving modest biosignatures intact (water, algae) but swamping the perception of anything more systemic? This idea of a random mask was the first thought that came to mind, before Jim noted that for steady signals, a 180 degree off-tuned countersignal would suffice.

    All pretty speculative of course.

  • Wojciech J September 15, 2013, 6:16

    I have been a long supporter of the idea that it is better on focus on more realistic targets like exoplanets and then follow up on biosphere signals than rely heavily on very far fetched scenarios envisioned by radio SETI(high energy intense radio signals beamed to our planet for millions of years). Needless to say without going into details of previous discussions that the chance of radio transmitting civilization in nearby space is extremely small.
    Additionally-as others mentioned here and as was mentioned in other discussions-the fact that our planet beams biosignatures for millions of millions of years, means that any advanced enough civilization to cross the stars knows of our planets’ existence. I might also add that with advanced telescopes they would be able to even detect our civilization since a couple of thousands of years(agricultural fields, night lights by ships and cities). So if we weren’t contacted it either means that they don’t care, don’t exist(question is they ever existed, or don’t exist now), keep us in isolation, or are too far away.
    In any case-next couple of decades should allow us to detect Earth like planets first and then biosignatures(if life exists). While I am too realistic to claim that it will be a revolution for whole society, it will certainly increase interest in space exploration and colonization to some degree.

  • Swage September 17, 2013, 5:37

    It may also mean we apply a pretty narrow view of sentience. In principle, when we talk about sentience, we mean something similar to us. However, considering a mind evolves initially specialized for its niche, the outcome may be quite unpredictable. It could be a group-consciousness in the style of an ant hive or bee hive, lacking any concept of individuality, for example. Their idea of communication may be pretty different from ours, if they have an idea at all. Then they may be also so advanced that they deem communication as impracticable in the same sense as you do not communicate with a butterfly. And genetically spoken, there is not that much difference between a butterfly and a human. To put it in Dr. Neil De Grasse Tyson words: we share 98.8% genetic code with chimps. All that technological capability is within those 1.2%. Now image something being 1% different from humans in the same direction we are different from chimps. That is a thought worth keeping in mind.

  • Eniac September 18, 2013, 22:17



    Astronist, above, politely calls this “True”, but then proceeds to name quite a few good reasons to think technological civilization immortal. Thereby, technically, proving you wrong. I have to agree with him….

  • Paul Gilster September 19, 2013, 8:44

    Well I can’t deny that, Eniac. I said there were no reasons, and Stephen promptly produced some good ones. Next time I’ll re-phrase…

  • ljk December 6, 2013, 10:30


    Hearing on Astrobiology

    By Keith Cowing on December 4, 2013 11:09 AM.

    Testimony of Dr. Sara Seager, Hearing on Astrobiology

    “We stand on a great threshold in the human history of space exploration. On the one side of this threshold, we know with certainty that planets orbiting stars other than the Sun exist and are common. … On the other side of this great threshold lies the robust identification of Earth-like exoplanets with habitable conditions, and with signs of life inferred by the detection of “biosignature gases” in exoplanetary atmospheres.”

    Testimony of Dr. Mary A. Voytek, Hearing on Astrobiology

    “Even today, children wonder, where did I come from? Astrobiology seeks to answer this enduring question.”

    Testimony of Dr. Steven J. Dick, Hearing on Astrobiology


  • ljk December 9, 2013, 23:37


    Alien-hunting equation revamped for mining asteroids

    Updated 11:06 05 December 2013 by Jacob Aron







  • ljk January 22, 2014, 0:39


    Emerging Technology From the arXiv

    January 20, 2014

    Are We Alone? NASA’s 30-Year Goal to Answer Astrophysics’ Greatest Question


















    Ref: http://arxiv.org/abs/1401.3741 : Enduring Quests-Daring Visions (NASA Astrophysics in the Next Three Decades)