After seven months of electronic hibernation, Philae has awakened on the surface of Comet 67P/Churyumov-Gerasimenko and resumed relaying its data to Earth.
When scientists at the European Space Agency last heard from Philae, early on November 15th, the washing-machine-size lander had survived an unexpectedly rough-and-tumble arrival on the surface of Comet 67P/Churyumov-Gerasimenko and managed to relay a substantial amount of data to Earth before exhausting its onboard batteries. The transmissions ended sooner than expected, after only 57 hours, because Philae had wedged itself in a heavily shadowed location that offered little direct sunlight to recharge its batteries.
Ever optimistic, ESA's engineering and science teams never stopped believing that the comet's changing solar geometry would eventually provide enough sunlight to bring the lander out of its electronic hibernation. That's now happened, as a joyful ESA press release announced earlier today. About 85 seconds of telemetry reached Earth late yesterday, relayed via the comet-orbiting mother ship Rosetta, at 20:28 Universal Time.
Philae appears to be in good shape despite seven months of inactivity, reporting that its internal temperature is –35ºC and that it has 24 watts of electricity available. Apparently the lander revived sometime before yesterday. "We have also received historical data," notes Stephan Ulamec, who heads the Philae team from the German Aerospace Center (DLR).
ESA engineers are awaiting further transmissions from the lander, which can only occur when Rosetta is within view. So far 300 packets of data have been received, but more than 8,000 data packets are stored in Philae’s mass memory. Those data should reveal details about the comet's activity over the past few days.
Ever since it fell silent, efforts to figure out exactly where Philae landed on the comet's very irregularly shaped nucleus. Using visual and radio tracking after the landing last year, combined with a radio beacon from the CONSERT radar experiment aboard Philae, searchers had recently narrowed the possible landing sites to a few areas. Close-ups taken after the landing in mid-December even revealed a tantalizing bright spot that, perhaps, revealed Philae amid a rubble field. Presumably, now that it's transmitting again, a firm location can be quickly established.
More importantly, a healthy Philae can potentially add important ground-zero measurements as the nucleus of Comet 67P becomes more active en route to its perihelion on August 10th.