A Nasa spacecraft that will hurtle past Pluto on Tuesday at more than 45,000 kilometres per hour has revealed the dwarf planet to be larger than scientists thought. 
 
 Fresh measurements from New Horizons, the first spacecraft to reach Pluto on the outer edge of the solar system, show that it is 2,370 kilometres across, roughly two-thirds the size of Earth’s moon. 
 
 
 
 Alan Stern, the lead scientist on the $700m (£450m) mission, said the increased dimensions meant Pluto must hold more ice and less rock beneath its surface than researchers had expected. Pluto has been hard to measure with any accuracy from Earth because it is so far away, and its atmosphere creates mirages that can fool ground-based telescopes. 
 
 Other instruments onboard New Horizons confirmed that Pluto’s north pole bears an icy cap. The latest measurements beamed to Earth from the probe picked up chemical signatures of methane and nitrogen ice in the polar cap. 
 
 
 
 One early image received from New Horizons last week showed Pluto as an orangey globe bearing a large bright spot shaped like a heart. More recent images have revealed cliffs, craters and chasms larger than the Grand Canyon. 
 
 “The science we’ve already made is mouth-watering,” said Stern. “The Pluto system is enchanting in its strangeness and its alien beauty.” 
 
 
 
 New Horizons will perform its historic flyby at 12.49pm BST on Tuesday. But scientists must wait until 2am BST on Wednesday for the probe to make contact with Earth and confirm it has survived the encounter. 
 
 The most dangerous hazards for New Horizons are dust particles trapped in orbit around Pluto after being dislodged from its moons by meteorite impacts. A strike from a dust particle the size of a grain of rice could destroy the spacecraft, but the risk of such a disaster is low, at around one in 10,000. 
 
 
 
 The New Horizons spacecraft has spent more than nine years on its 4.8bn kilometre journey to Pluto, the last world in the solar system to be visited by a spacecraft. On board are seven sophisticated instruments and the ashes of Clyde Tombaugh, the astronomer who discovered Pluto in 1930. 
 
 
 
 Sorry, your browser is unable to play this video. Facebook Twitter Pinterest 
 
 When the probe blasted off in January 2006, Pluto was the ninth planet in the solar system. Seven months later, astronomers at the International Astronomical Union voted to downgrade the icy body to a dwarf planet, because it does not dominate its region of space in the way the other major planets do. 
 
 
 
 The spacecraft will take scores of photographs as it speeds past Pluto and its five known moons, Charon, Hydra, Nix, STyx and Kerberos. The images will give the first close-up view of the mountains and valleys of the unknown world, and its tenuous atmosphere seen as the sun rises and sets behind it. Instruments on New Horizons might even find evidence that it snows on the tiny world. 
 
 
 
 Nasa officials expect the first images from the flyby to be released on Wednesday night. The snapshots from onboard cameras will capture details up to 100 metres across, a vast improvement on those taken on approach, which pick out features about 15 kilometres across. 
 
 But scientists are in for a long wait to learn everything New Horizons sees. The probe will collect so much information as it passes Pluto that it will take 16 months to send it all back to Earth. 
 
 
 
 The mission marks the end of the US space agency’s bid to explore every planet in the solar system, starting with Venus in 1962. Tuesday’s flyby coincides with the 50th anniversary of the first ever fly-by of Mars by the Mariner 4 probe. ||||| Image copyright NASA/JHU-APL/SWRI Image caption Pluto (R) and Charon (L) are the key targets for observation during the flyby 
 
 Nasa's New Horizons spacecraft has begun the most intense period of its encounter with Pluto. 
 
 The probe is set to hurtle past the dwarf world on Tuesday, grabbing a mass of pictures and other science data. 
 
 Controllers got a last health status report, before the robotic craft turned its antenna away from the Earth to concentrate on its target. 
 
 Only when New Horizons has its trove of images safely in its onboard memory will it call home again. 
 
 This is not expected to happen until just after midnight (GMT) into Wednesday. 
 
 It means there will be a long, anxious wait for everyone connected with the mission, as they hold out for a signal that will be coming from almost five billion km away. 
 
 New Horizons' flyby of 2,370km-wide Pluto is a key moment in the history of space exploration. 
 
 Its successful execution will complete the initial reconnaissance of the "classical" nine planets in our Solar System. 
 
 It will mark the fact that every body in that system - from Mercury through to Pluto - will have been visited at least once by a space probe. 
 
 Image copyright NASA Image caption The robotic probe turns its antenna away from Earth during the flyby 
 
 New Horizons has been returning a steady stream of information on approach to the dwarf world in recent days, but this will be as nothing compared to the huge number of observations it plans to acquire when passing just 12,500km from the surface. 
 
 This is timed to occur at 11:50 GMT (12:50 BST). 
 
 The probe will investigate not only Pluto but also its five moons: Charon, Styx, Nix, Kerberos and Hydra. 
 
 To achieve that, it must perform a furious set of manoeuvres as it points every which way in the sky to get the images and other types of data it needs. 
 
 "I can't wait to get into the data and really start making sense of it. Right now, we're just standing under the waterfall and enjoying it," New Horizons' principal investigator, Alan Stern, told BBC News. 
 
 Just getting the probe in position to make the flyby has been a monumental feat. 
 
 Because the observations are all run on an automated command sequence, New Horizons must fly a perfect path past Pluto, and with perfect timing - otherwise its cameras will shoot empty sky where the dwarf or its moons are expected to be. 
 
 This has necessitated aiming New Horizons at a "keyhole" in space just 100km by 150km (60miles by 90 miles), and arriving at that location within a set margin of 100 seconds. 
 
 All this has been achieved after a multi-billion-km flight across the Solar System lasting nine and a half years. 
 
 The mission team will not celebrate until New Horizons contacts Earth again, which should happen at 00:53 GMT Wednesday (01:53 BST). 
 
 This communication will contain only engineering information on the status of the probe, but controllers should be able to tell very quickly whether the flyby sequence worked properly or not. 
 
 The first high-resolution pictures from the pass should be downlinked later on Wednesday. 
 
 There is a very small possibility that New Horizons could be lost as it flies through the Pluto system. 
 
 Any stray icy debris would be lethal if it collides with the spacecraft at its 14km/s velocity (31,000mph). 
 
 As an insurance policy, the mission team therefore downlinked one last set of data from all seven of the probe's instruments on Monday. 
 
 This included a final full-frame picture of Pluto before the approaching dwarf filled the entire field of view. This image is expected to be released by Nasa on its website at the moment of closest approach on Tuesday. 
 
 Media caption Prof Alan Stern says Pluto is "a little larger than anticipated" 
 
 On Monday, the New Horizons team announced a new, more precise measurement of Pluto's diameter at 2,370km. The probe sees the girth of Charon to be very similar to earlier estimates, at 1,208km. 
 
 Nix is estimated to be about 35km across, and Hydra about 45km in diameter. Kerberos and Hydra are a lot smaller, but New Horizons has not yet been able to make a good determination of their size. This will come from the flyby data. 
 
 Image copyright NASA Image caption How Pluto and its biggest moon, Charon, compare in size to the Earth 
 
 The BBC will be screening a special Sky At Night programme called Pluto Revealed on Monday 20 July, which will recap all the big moments from the New Horizons flyby. 
 
 Follow Jonathan on Twitter. ||||| Ahead of Tuesday's historic flyby, NASA's New Horizons spacecraft has already delivered data that 'is a gift for the ages.' Among the discoveries: Pluto is bigger than previously thought. 
 
 Will Macy's become the next store to drop the Ivanka Trump brand? 
 
 On the eve of NASA's historic flyby of Pluto, scientists and tourists at the Lowell Observatory in Flagstaff, Arizona are excited about the images and discoveries the New Horizons' spacecraft will beam back to Earth. 
 
 NASA's New Horizons mission to the Pluto-Charon system has yet to mark its finest hours – a historic flyby that makes its closest approach to the binary planet and its moons Tuesday morning. 
 
 But even as the spacecraft puts the wraps on its final approach, data New Horizons has delivered within the past 48 hours "is a gift for the ages," says Alan Stern, a planetary scientist at the Southwest Research Institute in Boulder, Colo., and the mission's principal investigator. 
 
 The craft's approach is revealing "tremendous diversity between the two planets in the system and their moons," he said. "We're already seeing complex and nuanced surfaces that tell us of history for these two bodies that is probably beyond our wildest dreams." 
 
 In short, "the Pluto system is enchanting in its strangeness and alien beauty," Dr. Stern said during a briefing Monday. 
 
 How alien? 
 
 It's as though "we're on the bridge of the Enterprise approaching some alien planet around Alpha Centauri 3 or whatever it is," said Paul Schenk, a planetary geologist at the Lunar and Planetary Institute in Houston and a member of the New Horizons science team. "It's like someone painted it for a 'Star Trek' episode." 
 
 Even seemingly mundane measurements, such as a new, more-accurate determination of Pluto's size – now pegged at 1,473 miles across, at the high end of estimates that have ranged from 1,429 miles to around 1,491 miles – carry import. 
 
 The new size, combined with long-established, precise measurements of Pluto's mass, yields a dwarf planet a bit less dense than previously estimated. That means its interior contains more ice, versus rock, than previously estimated. This change has implications – yet to be worked out – for the process that formed the binary-planet system as well as for the chemistry of the disk of dust, gas, and ice that encircled the sun and provided the building blocks for the planets ad their moons, Stern explained. 
 
 Bragging rights also come into play. 
 
 "The new measurement unambiguously settles the debate about the largest object in the Kuiper Belt," Stern said, referring to a region of the solar system extending more than 2 billion miles beyond Neptune. By some estimates, the region hosts trillions of comets as well as several hundred thousand objects larger than 60 miles across. It's also the region that gave birth to Pluto and the object that would collide with it to form Charon. Another Kuiper Belt inhabitant, Eris, had previously laid claim to the "largest" label at 1,445 miles across. 
 
 A larger Pluto also means that the lower layer of the atmosphere is shallower than previously thought, which will affect models that try to shed light on the atmosphere's structure and behavior. 
 
 Another early result involves nitrogen escaping from Pluto's tenuous atmosphere. New Horizons' instruments began to pick up the great escape five days ago, when the craft supposedly was too far away to see it, Stern said. It could mean that the nitrogen is fleeing the planet at a higher rate than models have suggested or that the mechanism responsible for triggering the loss is different than researchers have anticipated. 
 
 In addition, incoming data show that a hypothesized polar cap on Pluto is in fact an ice cap consisting of nitrogen and methane ices. 
 
 New Horizons also is revealing features on Pluto that are generating speculation, pending more detail from measurements taken at the closest approach. 
 
 For instance, images of Pluto released over the weekend show a surface that in many places hosted vast expanses of small, tightly packed dimple-like formations. 
 
 The features appear to be similar to those on Neptune's moon Triton, Dr. Schenk said. Triton – itself thought to be a Kuiper Belt object that Neptune captured – hosts a surface "that looks like a boiling pot of porridge, with cells of material popping up. They create a cellular pattern that looks like the skin of a cantaloupe." 
 
 There, researchers suspect that relatively buoyant rock or ice has risen from deeper in the crust to build the array of hills and depressions – similar in principle to salt domes that rise through surrounding rock to form low hills in southern Louisiana or southeastern Texas. 
 
 The science team hopes to get a closer look at some of these dimpled regions in images New Horizons takes during its closest approach Tuesday morning. 
 
 In addition, images so far show a relatively smooth surface over much of Pluto, suggesting that the surface could be relatively young, Schenk said. 
 
 Again, he cites Triton as a possible analog. The relative smoothness of much of Triton's surface suggests that it's less than 100 million years old. "On Triton, everything is very young," Schenk said. 
 
 It speaks to Triton as a captured Kuiper Belt object whose orbit around Neptune initially would have been elliptical, but over time became circular. The change in orbit would have heated Triton significantly, allowing fresh material to well up from depth and repave the surface, erasing any evidence of impact craters that would have accumulated over time. 
 
 On Pluto, "we're not seeing any large craters that would pop out and say: There's a big basin here," he says. "So we're beginning to think that maybe that it's a very young surface." 
 
 The source of internal heating required to provide material for repaving Pluto is unclear, Schenk acknowledges. Perhaps heat left over from the impact that formed Charon remained intense enough long enough to provide sources of fresh material for resurfacing Pluto. 
 
 "We still don't know," he says. "But we'll find that out." 
 
 [Correction: This article has been updated to correct the new measurements of Pluto's diameter.]
– This is one of the biggest days in the exploration of our solar system since Voyager 2 approached Neptune in 1989—and there may not be a day like it again. According to NASA's calculations, its New Horizons spacecraft flew by Pluto at 31,000mph at 7:49am EDT today; confirmation of that will come tonight, some 13 hours later, reports the AP. The confirmation will mark the completion of NASA's tour of the "classical nine" planets, reports the AP, which notes that Pluto was considered a full-fledged planet instead of a dwarf one when the probe began its journey in 2006. Some things to know about the historic flyby, which comes 50 years to the day after the first successful flyby of Mars: New Horizons will have to capture a vast amount of data in a short time. The probe will be pushed to its limits as it pivots to capture photos and information on Pluto and its moons Charon, Styx, Nix, Kerberos, and Hydra during the flyby. "I can't wait to get into the data and really start making sense of it. Right now, we're just standing under the waterfall and enjoying it," principal New Horizons scientist Alan Stern tells the BBC. We don't know whether it was a success. The probe is far too busy to "phone home," the AP notes, but it's expected to send a confirmation signal at around 9pm tonight. The eagerly awaited first photos from the flyby should be released tomorrow night, the Guardian reports, though it will take 16 months to send all the data from the flyby back to Earth. We've already learned a lot of new things about Pluto. "The science we've already made is mouth-watering," says Stern. "The Pluto system is enchanting in its strangeness and its alien beauty." Among NASA's findings in recent days: Pluto's North Pole has an icy cap and the planet's diameter is 1,597 miles across, not 1,471 miles as previously thought. The finding suggests the planet contains a lot more ice and a lot less rock than thought, the Christian Science Monitor reports. There are still a lot of mysteries to be solved. Scientists hope the first close-up look at Pluto's surface will explain features like heart- and doughnut-shaped features recently spotted for the first time. LiveScience notes that new information from Pluto could help explain how our own planet formed and how life began. "There's a feeling among scientists that Pluto probably will tell us what the early solar system looked like and it's now locked in deep freeze and maybe it will tell us what we once were, a long time ago," the director of the Deep Space Communication Complex tells Reuters. The Australian facility will be first to receive new information from the spacecraft. New Horizons isn't done. New Horizons will keep traveling into the Kuiper Belt debris field and beyond after it passes Pluto, National Geographic notes, and it may have more research to do if NASA approves funding. (The astronomer who first spotted Pluto in 1930 is the spacecraft's only passenger.)