Philae lander goes to sleep after roller coaster ride on a comet

Fifty-six hours after landing on the surface of a comet, Philae sent one more round of data about its new home across 310 million miles of space. Then, its power went out.

"@Rosetta, I'm feeling a bit tired, did you get all my data? I might take a nap..." read a message on the @philae2014 Twitter feed.

The Rosetta mission's twitter response: "You've done a great job Philae, something no spacecraft has ever done before."

And then later: "S'ok Philae, I’ve got it from here for now. Rest well..."

All the experiments on board the lander had a chance to run and return information back to Earth. Philae's instruments scooped up material from the comet's surface, took its temperature, sent radio waves through its nucleus, and went hunting for hints of organic material. Cameras took the first panoramic images from the surface of a comet.

Infographic: Rosetta probe's mission, step-by-step

It has been a whirlwind ride for the lander, which was dropped onto the surface of the mountain-sized comet 67P/Churyumov-Gerasimenko on Wednesday morning. Two harpoons that were designed to tether it to the surface failed to fire, and scientists say the lander made two bounces before becoming stable. The first bounce caused the lander to go one-third of a mile into the air.

Friday morning, ESA officials expressed concern that the lander would not have enough battery power left to send back any more data from experiments it was conducting on its new, icy home. 

When Philae landed on the comet on Wednesday, it had enough battery power for about 60 hours of work. Scientists initially hoped that it would continue to operate on solar power, but the lander seemed to have settled in a hole on the comet, where it was surrounded by rock-like structures that block the sun.

Stefan Ulamec, the lander manager from DLR, said the that one of the solar panels on the lander was getting about an hour and 20 minutes of sunlight a day. Two other panels got just 20 to 30 minutes a day, he said.

At a news conference Friday morning before the last signal was received, Ulamec said it was possible that scientists would not hear from the lander again.

"We are hoping to get contact again this evening, but it is not secured," he said. "Maybe the battery will be empty before it talks to us." 

Happily, that turned out not to be the case. On Friday evening, ESA reported that all the science experiments had been deployed, and that the lander had been rotated 35 degrees in an attempt to get more sun on one of its larger solar panels. 

There is a chance that as the comet flies closer to the sun, the increase in solar energy will allow ESA to communicate with Philae once again.

ESA officials say the odds of that happening are small, but with Philae, the little lander that could, anything is possible.

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