Comebacks don't come much bigger than this one: The European Space Agency (ESA)'s Philae comet lander has woken up, albeit for just eighty-five seconds. The news has been announced via Twitter, and the ESA is optimistic this will be just the first revival of many.
In possibly the biggest science story of the last year, the ESA put Rosetta into orbit around comet 67P/Churyumov-Gerasimenko, followed by the first ever landing of a spacecraft on a comet's surface.
Philae collected hugely valuable data over the next 60 hours, which will be studied for years to come. Unfortunately however, its batteries ran out. Philae was designed to replenish itself with solar power, but it landed in what was suspected to be the shadow of a crater rim.
The ESA expressed hope circumstances would change; Churyumov-Gerasimenko is still heading in towards the sun, with closest approach on August 13.
Orbital changes had potential to provide several benefits. Comets have seasons too, and if Churyumov-Gerasimenko's tilt turned Philae's location towards the sun it would get more hours of light in a day. Moreover, solar intensity is increasing as the comet approaches the sun. Finally, since comets sublime away as they reach the inner solar system, the inconvenient ridge doing the shadowing might shrink.
As of December, Philae's lead scientist Jean-Pierre Bibring was telling a news conference that “Pessimistically [a wake up] will be after Easter,” but that one early this year was a strong possibility. The ESA also proclaimed how, if Philae could just get enough sunlight to function, its location would be a benefit, allowing it to study not only the ground beneath its feet, but also the bits of the comet now hiding the sun.
However, as the days ticked away, the public became cynical. Mission scientists never gave up hope. Just three days ago analysis of images taken by Rosetta last year hinted at Philae's exact landing site, something unconfirmed until now. Making the announcement, lander project Manager Dr Stephan Ulamec said, “The conditions for Philae's wake-up are becoming more and more favorable as the comet approaches the sun.”
Now indeed, the greatest comeback since Lazarus has occurred. Just after midday Greenwhich Mean Time Philae's Twitter account, after seven months of silence, tweeted “Hello Earth! Can you hear me? #WakeUpPhilae”. This was followed by a brief interchange with @ESA_Rosetta, which reacted pretty much as any doting parent would on hearing from a longlost child.
Image tweeted by Rosetta to celebrate Philae's rebirth. Credit:ESA
At time of writing the last tweet reads “Oh, OK @ESA_Rosetta! I'm still a bit tired anyway...talk to you later! Back to #lifeonacomet!”
Lander control had picked up 300 data packets from the spacecraft a few hours earlier, but verified their reliability before releasing the information to the world.
"Philae is doing very well: It has an operating temperature of -35ºC and has 24 Watts available," Ulamec reported. “The lander is ready for operations.”
Ulamec also reported the messages revealed that Philae had woken up previously, but signals had not got through. “We have also received historical data,” he said. Also in the messages is the fact that considerable data collected in the few days after Philae landed, but not yet received on Earth, remain in Philae's mass memory, and will hopefully be sent during future wakeful periods.