Last November, the washing-machine-sized robot launched from its companion satellite, Rosetta, towards a comet named 67P/Churyumov-Gerasimenko. It reached the comet, but the landing was rocky. Philae bounced across the surface, landing on its side in a ditch, and only had enough power to collect and transmit data for 57 hours. To the woe of scientists and space fans, Philae's batteries eventually drained, sending the robot into a deep, possibly permanent slumber.
There was always a chance Philae might wake up: The robot is equipped with solar panels. But in a cold, dark ditch on 67P, the panels had limited light. Scientists were never quite sure if it would gather enough light to reboot, but they hoped that as the comet approached the sun, it might be able to absorb more solar energy and recharge. The ESA was cautiously optimistic, as Eric Hand reports for Science.
Since March, the ESA's Rosetta team has been listening for a call from Philae. On June 13 at 10:28 pm German time (4:28 am Eastern Time on June 14 in the U.S.), they received an 85 second transmission containing over 300 data packets from the comet-borne robot. The message mostly contained data about its health and status. The ESA announced the news in a blog post on June 14.
Data in Philae's transmissions suggest that it may have been awake for a while and attempted phoning home previously with no success, as Ashley Yeager reports for Science News. To communicate with Earth, Philae must transmit to Rosetta, which trails the comet by 200 kilometers, and the signal between the two can be spotty, as Jonathan Amos explains for the BBC. So far the signal seems to be holding, as Amos writes, the robot phoned home again last night to send three short ten second messages and more data.
The data also suggest that things are looking up for this little lander. "While the information we have is very preliminary, it appears that the lander is in as good a condition as we could have hoped," ESA project manager Stephan Ulamec said in a statement posted June 15. Over the last three days, the robot's internal temperature has already risen from -35ºC to -5ºC, and it has 24 Watts of power available. Philae needs at least 19 Watts to communicate; with two good hours of sunlight each day maintaining contact should be feasible. The robot also has over 8000 additional data packets, meaning a lot more room to collect data about comet 67P and its surroundings.
The ESA team had already planned to move Rosetta closer to the comet. This could improve the signal strength between Philae and the satellite, Geir Moulson writes for the Associated Press. In the coming weeks, the ESA hopes Philae can generate enough power to do some cool science experiments on the comet's surface as it flies through space.