Philae Rises! What's Next for Rosetta's Comet Lander?

After a 7-month hiatus, the revived European comet lander is nearly ready to resume work, expanding on our scientific understanding of the solar system.

Perched on the surface of a comet, the revived Philae lander should soon be able to resume -- and possibly expand -- an unprecedented examination of organic material believed to date back to the beginning of the solar system.

Released by the Rosetta mothership, Philae floated down to the surface of Comet 67P/Churyumov-Gerasimenko on Nov 12, but its anchoring harpoons failed and the 220-pound probe shot back into space. It landed a second time, bounced and finally came to rest about a half-mile away with two of its three legs on the ground and wedged next to a cliff wall.

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Nevertheless, Philae ran through a 64-hour, pre-programmed series of experiments before its batteries died. The lander was supposed to set down in an area nearly always illuminated by the sun to recharge its batteries. Instead it ended up in shadow and fell silent.

Spacecraft controllers continued to use the orbiting Rosetta spacecraft to hunt for a signal from Philae while they waited for the comet to move closer to the sun, hoping the lander would recharge itself.

Over the weekend, Philae finally phoned home -- twice – rekindling scientists' hopes that the mission could resume.

First, though, flight controllers need to figure out when Philae will be in regular position to communicate with Rosetta, which is used to relay the lander's signals to Earth.

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"It's of utmost importance to see if we can get a stable communications pattern between the two machines," Rosetta deputy flight director Elsa Montagnon, with the European Space Agency, told reporters during a webcast press conference at the Paris Air Show.

"If we can do that, then we can do the next step and resume the scientific operation of Philae," she said.

Managers plan to reposition Rosetta a bit closer to the comet, which is becoming more active as it races toward the sun. The closest approach will be on Aug. 13. The comet is in a 6.5-year orbit around the sun that comes as close as between Earth and Mars and as far as beyond Jupiter.

Moving Rosetta is a bit risky because gas, dust and ice jetting from the comet can confuse the spacecraft's navigational cameras.

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"Imagine taking your car through a snowstorm -- you don't see very much. It's not very safe," Montagnon said.

However, the potential for more science from Philae, particularly as the comet undergoes dramatic changes from heating, makes the risk worthwhile, project managers said.

Philae completed about 80 percent of the studies planned during its initial mission, including operating a small drill intended to dig out samples for chemical analysis.

Because of the lander's angle, however, the drill didn't reach down far enough to collect samples.

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Scientists are keen to learn if the carbon-based material covering the comet's surface is similar to organics found on Earth. One test, for example, would assess the molecular asymmetry to determine its chirality, or handedness.

"We are optimistic now that this analysis can be realized in the upcoming weeks. Temperature and energy of Philae seem sufficient and very promising," Philae scientist Uwe Meierhenrich, an analytical chemist at the University of Nice Sophia Antipolis in France, wrote in an email to Discovery News.

Rotating Philae for drilling, however, will be among the last tasks ground control teams will attempt.

"We will start with something simple, not demanding too much power," and no movement of the lander, before attempting activities that are more complex and higher risk," said Barbara Cozzoni, with the German Aerospace Center's Philae lander control center in Cologne.

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Philae lead scientist Jean-Pierre Bibring sees a silver lining in the revamped plans. Had Philae landed as expected, it probably would have overheated by the end of March and died.

"We're in a shadow, with all the risk associated with that, but we have the capability now to wake up and possibly have a very long-term activity," Bibring said.

Results from Philae's initial run of experiments will be published in an upcoming issue of Science.

This was the first 360 degree observations of Philae's surroundings on the surface of Comet 67P/Churyumov-Gerasimenko in November, 2014. Shortly after these images were received, the lander fell silent after running out of battery power.

At 10:03 CET (4:03 am EDT) on Wednesday morning, the Rosetta mission's Philae lander separated from the Rosetta satellite to begin a 7 hour drop onto Comet 67P/Churyumov-Gerasimenko's surface. This image was taken just after separation by the lander's CIVA-P imaging system. One of Rosetta's 14 meter-long solar arrays can be seen in shot.

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Looking down, moments after separation, the Rosetta satellite can see that Philae's landing gear has deployed successfully.

Another view of Philae (the bright dot) descending into the dark after separation. Photo taken with Rosetta’s OSIRIS wide-angle camera.

Shortly before landing on Comet 67P/Churyumov-Gerasimenko, Philae's Rosetta Lander Imaging System (ROLIS) panoramic camera captured this stunning photo of the landing site, proving that it was on target. Philae was 3 kilometers (1.9 miles) from the comet's surface at the time.

Moments before landing, Philae's ROLIS camera captured this photo of the comet's dusty surface. The few rocks that can be seen appear to be embedded in soft, dusty regolith.

The Rosetta mission crew celebrates Philae successfully landing on comet 67P, at the European Operations Space Center in Darmstadt, Germany on Nov. 12, 2014.

The red cross marks the spot where Philae should have landed. Although the lander was originally on target and did touch down there, the robot bounced as it could not anchor itself, causing it to land, a second time, 1 kilometer away. Rosetta mission scientists believe Philae came to rest somewhere near the cliffs in the upper-right of this image of Comet 67P's surface.

The first two CIVA images confirmed that, on Nov. 12, Philae settled on the comet's surface and was able to take its first photographs. One of the lander’s three feet can be seen in the foreground.

This is the first panoramic view taken on a comet's surface. The view, unprocessed, as it has been captured by the CIVA-P imaging system, shows a 360 degree view around the point of final touchdown. The three feet of Philae’s landing gear can be seen in some of the frames.

More images will be posted when they become available.