The elation scientists and engineers felt when the Rosetta mission's lander set down Wednesday has been tempered by the discovery overnight that Philae didn't simply land.
It bounced—not once but twice—before coming to rest a significant distance from its original landing site on comet 67P/Churyumov-Gerasimenko.
The lander is still functioning, but its solar panels aren't getting enough power to keep Philae going for more than a few more days. The mother ship, orbiting overhead, is now searching for Philae with its high-resolution cameras.
Philae evidently bounced because a thruster failed—the thruster was meant to stabilize the craft during landing and push against the comet to hold it in place during anchoring. Harpoons that should have tethered Philae to the surface also failed to deploy. (See more on the landing process in our Viewing Guide.)
The first bounce lasted nearly two hours, said Jean-Pierre Bibring, the European Space Agency scientist in charge of the lander, at a press conference today. It took Philae about a half mile (one kilometer) back up into space, then slowly back, where it ended up a half mile or so away from where it first touched down. The second jump was shorter in time, altitude, and distance.
The good news is that Philae is still operating and sending data, and that it's stable for the moment. It could have landed on a steep slope, for example, but, said Bibring, "We're almost vertical, with one foot almost certainly in the air and two on the surface."
The bad news, made clear in photos released this morning, is that the probe is close to a cliff. The cliff's shadow is limiting how much sunlight the probe's solar panels can receive, which means Philae is depending largely on its batteries for power. That power could run out as early as Saturday.
Scientists had anticipated that the panels might not work even if the landing was smooth, since there was a chance that dust kicked up by the touchdown would have rendered them inoperable. Luckily, the science program was designed with the possibility of a very short lifetime in mind for Philae. (Read more about Rosetta's science in "Touchdown! Comet Landing to Offer Clues to Solar System's Birth.")
But it would be better, clearly, for the probe to work for much longer. There's still a chance that Philae can keep operating until the mission ends in December 2015, say scientists who are working on a plan to remedy the situation, if the lander is nudged into a better position.
Philae has a number of instruments designed to swing into place when deployed. If the craft were anchored as intended, with all three legs down, these swings wouldn't shift the probe's position. But without that anchoring, moving the instruments could move the lander, and that could shift Philae into a slightly sunnier spot.
European Space Agency scientists are considering their next move very carefully, since any of these movements could also topple the craft over completely.
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