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The ESA comet lander Philae came to rest between two shadowed cliffs, limiting the sunlight hitting the lander's solar panels, but scientists hope the lander can be revived by February as more light arrives. This image of the comet's surface is a mosaic of four taken by Rosetta's navigation camera on December 10.

Rosetta's Comet Lander Will Revive After Bumpy Touchdown, Scientists Say

Hopes rise for reviving the hibernating lander's solar power as comet receives more sunlight.

SAN FRANCISCO—Fear not for Philae: The little lost lander could reawaken as soon as February, the Rosetta mission team said Wednesday. Increasing sunlight almost guarantees an end to the probe's current hibernation on a comet racing toward the sun.

The European Space Agency's $1.75-billion mission sent the lander to comet 67P/Churyumov-Gerasimenko on November 12 in an audacious, if bumpy, touchdown on the double-lobed comet. It was the first soft landing attempt on a comet. (See "Touchdown! Comet Landing to Offer Clues to Solar System Origins.")

The lander bounced after an anchoring harpoon failed to fire, turning initial elation to disappointment. After a two-hour bounce, Philae came to rest with one of its three feet planted on the comet and the others angled between two shadowed cliffs.

Those cliffs allow, for now, only 4 hours and 33 minutes of uninterrupted sunlight per day to the probe's solar panels, not enough to restart it. But the mission team announced at the American Geophysical Union meeting that more sunshine is on the way.

"There is no doubt that we will wake up," says lead lander scientist Jean-Pierre Bibring of Institut d'Astrophysique Spatiale, in Orsay, France. "And I think we will be in good shape."

As the comet moves closer to the sun, its horizon is also rising, Bibring says. The combination of brighter sunlight with longer exposure should provide the five watts of solar-panel power needed to restart Philae, he says, perhaps as soon as February.

Rosetta managers still don't know the exact location of the spacecraft, but recently completed a three-day survey of the region of the comet where they believe it rests, based on images from its onboard cameras. The exact location should soon be sifted from that data, says Rosetta team scientist Matt Taylor of the European Space Agency.

The only real worry, Bibring says, is that the cold of the comet's surface could have damaged electronics aboard the sleeping Philae. But since those same electronics survived a ten-year trip through the equally cold depths of space, Bibring is optimistic.

Philae had run for a day on battery power after its final landing, completing several analyses of the comet's surface before shutting down. The team is still sorting through this data, Bibring reported, searching for clues to the composition of the comet, thought to be a 4.57-billion-year-old relic from the early days of the solar system.

Lucky Break?

Only about 2.5 miles (4 kilometers) long, the small comet has gravity several hundred thousand times weaker than Earth's, explaining why the lander bounced off the comet after harpoons failed to fire and anchor it.

"We had an exciting landing, more exciting than we expected," says Taylor. "But we think we ended up in a better place than we expected."

That's because the lander appears to be wedged against three distinct kinds of icy terrain, based on views from its landing cameras. The team hopes the ice and dust grains of the most deeply shadowed material might be unaltered since the early formation of the comet, billions of years ago.

"We picked a really good comet," says mission scientist Kathrin Altwegg, who described early findings from the Rosetta spacecraft, which is now circling about 19 miles (30 kilometers) above the comet. The orbiter has already detected complex carbon chemistry among the traces of comet stuff steadily released by comet 67P as it travels through space. (Related: "Rosetta Spacecraft Suggest Asteroids, Not Comets, Birthed Earth's Oceans.")

Here Comes the Sun

Comet 67P's warmest moments will come in August, when it zips to within 116 million miles (186 million kilometers) of the sun. As early as this spring, the warming comet should sprout a tail as bits of its surface begin to sputter off in the sunlight.

When that happens, the Rosetta orbiter will need to raise its altitude to avoid being "blown off" by the comet's tail. The spacecraft will occasionally dive through the tail and close to the surface of the comet, coming as close as six miles (ten kilometers) on at least one flyby in February.

Rosetta itself is expected to operate at least until December 2015, watching the comet as it recedes back into the depths of the solar system, its tail fading, on a 6.6-year orbit around the sun. The mission may extend even longer with additional funding, Taylor says—at least another year.

"The science is only beginning," Taylor says. "The science teams are already overwhelmed."

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