It began with a bumpy landing and ended with a touching tweet.
“I’m feeling a bit tired, did you get all my data? I might take a nap...” tweeted @Philae2014.
It was early on Saturday morning. After 57 hours performing science experiments on the surface of comet 67P/Churyumov-Gerasimenko, the audacious Philae mission was coming to an end. Not enough light was hitting its solar panels and the spacecraft was preparing to hibernate, but in true Hollywood style, Philae heroically managed to send back all of its data just before the curtain fell.
Contact was lost at 0:36am GMT, a few minutes before the end of the communications window.
Within the final blocks of data that Philae returned were readings from an instrument called COSAC, the Cometary Sampling and Composition experiment. They could reveal the molecular ingredients that became life on Earth, since comets are remnants from the formation of the planets 4.6 billion years ago. Their icy bodies preserve the primordial organic molecules that were incorporated into the Earth and led to the origin of life.
“The data collected by Philae and Rosetta are set to make this mission a game-changer in cometary science,” European Space Agency (ESA) Rosetta project scientist Matt Taylor said.
There is still a chance that Philae could be revived. The comet is beyond Mars, but in August next year, it will be close to Earth’s orbit and sunlight will be stronger.
“We still hope that at a later stage of the mission, perhaps when we are nearer to the Sun, we might have enough solar illumination to wake up the lander and re-establish communication,” said Stephan Ulamec, Philae lander manager at the German Aerospace Center (DLR).
In the meantime, the science teams are beginning to analyze the data sent back by the spacecraft. The first results are expected to be presented at the American Geophysical Union conference in San Francisco next month. The Rosetta mission is to continue for another 20 months, studying the comet and listening for Philae to wake up.
Philae touched down on Wednesday afternoon after a seven-hour descent from Rosetta. Earlier in the day, engineers realized that the thruster system on Philae was not responding. The thruster was designed to hold Philae onto the surface of the comet as harpoons were fired to anchor it. Without it, the landing would be much riskier.
At the moment of touchdown, the harpoon system did not fire. For a while, it looked as if Philae was stable. Celebrations began at the European Space Operations Center in Darmstadt, Germany. However, at the lander control center in Cologne, Germany, researchers saw a different story. Magnetic data showed that Philae was still moving.
Philae had rebounded from the surface. In the weak gravity of the comet, Philae’s bounce took nearly two hours to complete. It fell and bounced a second time — though for just six minutes. It came to rest just before the communications window closed for the night. So pictures had to wait.
When images arrived, scientists were confused. Designed to show a 360? panorama of the landscape and horizon, some showed rock, others showed space with stars. Philae had come to rest on its side.
“We are exactly below a cliff, so we are in a shadow permanently,” said Jean-Pierre Bibring, Philae’s lead scientist at the Institut d’Astrophysique Spatiale, Universite Paris Sud in France.
In the shadows, there was not enough light to charge the secondary batteries. Everything had to be completed within the 60-hour lifetime of the primary battery.
“We juggled everything so that every instrument got to do a measurement, so we are very happy with the mission so far,” said Valentina Lommatsch, a member of the DLR’s lander team.
From orbit, Rosetta was trying to locate Philae. Data from the radar system pointed to a resting place about 1km away from the touchdown, near the wall of a large depression.
Strategies for moving Philae included flexing the landing gear to try to make it “hop” out into the sunlight. Engineers ran out of time, but managed to rotate the probe so a larger solar panel was pointing toward the single shaft of sunlight that was reaching the lander.
“At the end of this amazing rollercoaster week, we look back on a successful first-ever soft landing on a comet,” ESA Rosetta mission manager Fred Jansen said. “We now look forward to many more months of exciting Rosetta science and possibly a return of Philae from hibernation.”
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