After a daring 7-hour descent, a miniature spacecraft settled safely onto the rugged surface of a comet 300 million miles from Earth this morning, provoking cheers of triumph and relief from scientists andengineers assembled at the mission control room in Germany.With the touchdown, the spacecraft, named Philae, entered the record books as the first to land on a comet.Its success will give scientists unprecedented insights into the target comet, a 4-billion-year-old world of dust and ice that holds secrets to the origins of the solar system.In a bravura performance, the little spaceship – about the size of a washing machine – cast off at roughly 4 a.m. ET from the mother ship that had carried it close to the comet. Then, as mission personnel waited in anxious suspense, Philae descended at a leisurely pace towardthe comet's rugged surface. There was no way to steer it on its way down, no way to change course and no going back.APThe image released by the European Space Agency ESA on Wednesday, Nov. 12,moreA few minutes past 11 a.m. ET, engineers received word that the spaceship, which belongs to the European Space Agency, had alighted safely on the comet's crater-scarred and boulder-filled landscape."We are sitting on the surface. Philae is talking to us," said a jubilant Stephan Ulamec, Philae lander manager. "We are on the comet."There were worries that the comet's surface "might be something like powdered sugar, and the lander would just go straight through," said the Finnish Meterological Institute's Walter Schmidt, head of the scientificteam for a Philae instrument that will measure the comet's ice levels over time.Engineers' joy was tempered by the realization that the two harpoons that were supposed to help anchor Philae to the surface of the comet didnot fire. The engineers were studyingwhy and whether to refire the harpoons.The landing was successful despite a potentially disastrous failure. Dismayed engineers discovered before the landing that a thruster to help keep Philae on the comet's surface wasn't working. In the end, it didn't matter.Philae and its carrier spacecraft Rosetta spent a decade just getting to the comet, launching from Earth in 2004 and finally pulling up in August next to comet Churyumov-Gerasimenko, also known as comet 67P. The comet, now more than 300 million miles from Earth, is tracing a 61/2-year oval around the solar system.Rosetta's arrival at 67P gave scientists a thrill: The comet wasn't potato-shaped as had been expected but a complex rubber-duck shape. For mission engineers, the comet's profile was a nasty surprise rather than an intriguing revelation. That irregular shape made it trickier for Rosetta to orbit the comet and drop the lander in exactly the right place on the mountain-sized comet.The comet's terrain also posed challenges. It is pocked with deep depressions and dotted with building-sized boulders, and it boasts slopes so steep that they make the toughest ski resort look tame. A lander that toppled onto its side would be worthless. So would a lander that bounced off the comet's surface.Engineers aimed Philae at a relativelygentle landing zone, but they admitted before the spacecraft set off on its own that a safe arrival was not guaranteed."There is no doubt we will hit the comet," Andrea Accomazzo, Rosetta flight director, said before the landing. "Whether we hit it safely is another matter. … We have to be a bit lucky."And they were. After Rosetta gave Philae a gentle shove, the lander drifted gently toward the comet, touching down on its three spindly legs at walking speed. Ice screws on its three feet bit into the surface, described by Rosetta project scientist Matt Taylor as something between packed snow and cigarette ash. In the end, it didn't matter that a thruster that was supposed to help keep the spacecraft on the surface malfunctioned."It's a difficult procedure … There are so many uncertainties,"said Gostar Klingelhoefer, head of the scientific team for an instrument that will analyze the comet's chemical composition and a planetary scientist at Johannes Gutenberg University in Germany."It was a big relief, I have to say."Now begins a frenzy of data gathering. The comet is drawing closer to the sun, which will eventually bring Philae's scientific career to an end, probably next March. The lander's 10 scientific instruments will snap pictures, sample chemicals, drill into the ground and more, hoping to learn more from this object made of scrapsof the stuff that went into the formation of the planets. Eventually managers may command Rosetta too to make a soft landing on the comet's surface, reuniting the two spacecraft once more.
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