The European Space Agency’s Rosetta mission has finally found its Philae lander, nearly two years after the vehicle became the first ever to land on a comet. The mission team has struggled to locate the lander since that historic touchdown, and communications with Philae have been sparse to non-existent. But less than a month before the Rosetta mission was set to end, the Rosetta spacecraft — which is in orbit around the comet Philae landed on — has at long last imaged the little lander on the comet’s surface.
"It is incredible we have captured this at the final hour."
"This remarkable discovery comes at the end of a long, painstaking search," Patrick Martin, ESA’s Rosetta Mission Manager, said in a statement. "We were beginning to think that Philae would remain lost forever. It is incredible we have captured this at the final hour."
And now ESA understands why it’s been so hard to communicate with Philae. The Rosetta images, taken on September 2nd, show that the lander is in a particularly rocky patch of the comet and in the shadow of a large boulder. That could also explain why Philae has had such a hard time functioning. The lander is powered by solar panels, but it probably didn’t receive a lot of sunlight in such a shadowed area. "The position, as we find in this image, did not help at all," Martin tells The Verge.
Plus, Philae is at a strange orientation. The lander looks to be nearly sideways on the surface, with one of its legs wedged inside a crack. That means the lander’s antenna is pointing toward the rocks rather than out into space. Given this position, it’s no wonder the Rosetta spacecraft has had a hard time picking up signals. And it could explain why the signals Rosetta has received from Philae haven’t been very strong. "It’s problematic if your signal is coming out of the top of your head, but you’re lying on the floor in a ditch," Matt Taylor, a Rosetta mission scientist, tells The Verge.
When Philae descended to the comet’s surface on November 12th, 2014, it was supposed to deploy harpoons that would help it anchor to the comet. But those harpoons failed to fire and Philae bounced off the comet instead. It then flew for an extra two hours before landing in the spot it’s in now.
It’s too late to hear from the lander ever again
Once it finally came to rest, Philae conducted a good bit of science for its first three days on the comet. But since it wasn’t receiving enough sunlight, the lander eventually exhausted its onboard batteries and went into hibernation mode. ESA was hopeful that Philae might receive enough sunlight again once the comet got closer to the Sun on its orbit, and that seemed to be the case in summer of last year. The Rosetta spacecraft picked up some sporadic signals from Philae in June and July of 2015. But Rosetta hasn’t heard from the lander since.
It’s now too late to hear from the lander ever again, even though scientists have pinned down its location. In July, ESA switched off Rosetta’s Electrical Support System Processor Unit, the system the spacecraft uses to communicate with Philae. It was powered down in preparation for the end of the Rosetta mission on September 30th, when the Rosetta spacecraft is scheduled to crash land into the comet.
Knowing the exact location of Philae is still good news
However, knowing the exact location of Philae is still good news. Now, ESA researchers can put the lander’s scientific observations in context with the vehicle’s surroundings. That will help strengthen the mission team’s findings. "It means we can do more science with that data set than without knowing the lander’s location," Taylor says.
And it answers one of the ultimate questions that has plagued the Rosetta mission since Philae’s landing. The mission team had a general idea of where the lander was located, but no one could be certain without photographic evidence.
"Psychologically it’s giving us closure now," Taylor says.