Time is running out for the Philae comet lander. The latest attempts to communicate with the probe have failed. And with temperatures plummeting as the comet races from the sun, it will soon be too cold for the robotic explorer to keep its computer running.
On January 10, engineers sent a command to spin Philae’s reaction wheel, which helped stabilize the lander during its descent. They hoped to nudge the lander into sunlight or at least shake several months of comet dust off its solar panels. Philae did not respond.
“It’s a bit sad,” says Stephan Ulamec, Philae’s manager at the German Aerospace Center in Cologne. “But it would be sad if we concentrated so much on what we couldn’t achieve and not on what we did.”
Philae’s mission got off to a rough start (SN: 12/13/14, p. 6). After separating from the Rosetta spacecrafton November 12, 2014, Philae bounced across comet 67P/Churyumov-Gerasimenko and settled against cliffs where there was not enough sunlight to keep the power on. Philae spent just 55 hours investigating its new home before shutting down. As the comet moved along its orbit, Philae’s solar panels spent more time in the sun. Seven months after going quiet, Philae phoned home after its batteries recharged (SN Online: 6/14/15). Contact with the lander has since been intermittent, with its last communication — a 12-minute burst of data from its radar instrument — sent July 9.
“The situation gets worse every day,” says Ulamec. “There’s little reason to believe that if the lander doesn’t wake now, it will wake in worse conditions in a few weeks.” As the comet travels farther from the sun, less solar power is available to the lander. By the end of January, temperatures will have dropped below −51° Celsius, Ulamec says, at which point the computers will no longer boot up.
“The fact that it worked at all is miraculous,” says Jessica Sunshine, a planetary scientist at University of Maryland in College Park. Before Rosetta launched in 2004, researchers knew very little about what comets are like up close. Landing on a comet “was a gutsy thing,” she says.
During its brief active tenure on the comet, Philae got the first intimate pictures of any comet and detected a fog of organic compounds. Its radar found that 67P is porous and uniform throughout. “That was a fantastic measurement,” says Sunshine. The lack of layers in the comet’s interior suggests that 67P was put together gently, which means the nucleus is a time capsule carting around a preserved sample of detritus from which the solar system formed 4.6 billion years ago (SN: 8/22/15, p. 13).
Philae and Rosetta showed that features both tiny and enormous look similar on the comet, says Sunshine. Without context, it’s hard to distinguish between the rugged terrain around the lander and the cliffs towering about 900 meters over the comet’s midsection. “That’s telling us something about how this comet was put together and evolved,” she says. “These datasets are going to stand the test of time.”
Philae might be done exploring, but it won’t be forgotten. Ulamec hopes to get some images of Philae this summer as Rosetta cozies up to get a closer look at how 67P changed during its closest approach to the sun. At the end of the mission in September (SN Online: 6/23/15), engineers will direct Rosetta to crash on the comet, snapping pictures all the way down. “It won’t be a proper landing,” says Ulamec. But at least Philae will finally have some company.