Philae, the space probe that made history when it landed on a comet in November 2014, is awake. The European Space Agency (ESA) announced today (June 14) that it had received signals from the comet lander last night, at 22:28 Central European Standard Time. They were the first in over seven months.
Excited scientists on the mission told Nature that Philae has probably been awake for a few days and that they hope the lander will start some low-risk science activities in the coming days—assuming that Philae makes contact again.
"Philae is doing very well: It has an operating temperature of -35ºC and has 24 Watts available," said ESA project manager Stephan Ulamec of the German Aerospace Centre (DLR) near Cologne, according to an ESA statement. "The lander is ready for operations."
ESA says that for 85 seconds Philae “spoke” with ESA ground control via the spacecraft Rosetta, which is orbiting 67P.
As the news got out that Philae had called home, mission scientists reacted on Twitter. “I’m in tears again ..can it be true?” wrote Monica Grady, a planetary scientist at the Open University, based in Milton Keynes, UK, and a co-investigator on Philae's chemical analyzer, Ptolemy.
The news ends months of speculation over whether the washing-machine-sized lander would ever regain contact with Earth (see: “Five factors that will decide if Philae wakes”).
Philae's batteries ran out on November 15, just three days after it bounced on to comet 67P/Churyumov–Gerasimenko, following a perilous descent. Stuck in the shade, it was unable to charge its solar-powered battery and entered hibernation.
Ever since, scientists have consoled themselves with the hope that the craft is not dead, just sleeping, and that it would regain power as comet 67P neared the sun.
ESA also says that Philae sent back historical data showing that the comet lander was awake earlier but was then not able to contact ESA.
According to ESA, there are data in Philae’s memory that will shed light on “what happened to the lander in the past few days.” ESA is now waiting for the next contact from the spacecraft.
The available power—24 watts—is a “good amount,” says Koen Geurts, a member of the landing team at the DLR. “It’s more than enough to communicate and to do science activities,” he says. Philae has probably been awake for several comet days, which each last 12.4 hours, but it is not yet clear how many, he adds.
Assuming the connection with Philae reopens, the first science in coming days will likely be low risk activities, he says, such as taking images and turning on the ROMAP instrument, which measures the comet’s magnetic field.
Delightful phone call
The lander team were growing concerned about Rosetta’s ability to fly in close enough to hear from Philae, given the increasing dust and gas activity as the comet flew closer towards the Sun. “There was a general feeling that if Philae doesn’t wake up soon it might become too late. We were all delighted when we got the phone call last night,” Geurts says.
The lander team is currently trying to understand why the link-up from Philae lasted less time then they would have predicted: from a two-hour window, the connection lasted only about 2 minutes. This might be due to uncertainties in Philae’s orientation, or the lander may have moved, Geurts says.
The team in charge of the Rosetta orbiter, which passes the signals from Philae to Earth, will now focus on maximizing the connection, says Matt Taylor, ESA project scientist for the Rosetta mission. “We have to update how we think the lander is oriented when the orbiter comes past,” he says.
In the short term, the orbiter will change its planned orientation to point directly at the lander, he says, and in the long term, the orbiter may eventually change trajectories to aid communications, he adds. "There are still a lot of things to be confirmed with respect to the health of the lander and what we can learn from it. But everyone is very excited,” he says.
The news of Philae's revival comes days after reports of a possible sighting of Philae on comet 67P. Though scientists knew Philae had landed in November, they didn’t know where it had ended up because the touchdown was rough and the probe bounced twice.
This article is reproduced with permission and was first published on June 14, 2015.
Nature News doi: 10.1038/nature.2015.17756