IN NOVEMBER, A spacecraft made a dramatic, first-ever landing on a comet\u2014three times. After the Philae lander touched down on comet 67P\/Churyumov-Gerasimenko, the harpoons that were supposed to latch it onto the surface didn\u2019t fire, and instead, the spacecraft bounced back into space before returning to the comet. Another shorter hop then took it to its current, shady resting spot. Since then, the Philae lander has been slumbering in the cold and dark some 286 million miles away, with only meager recharging from its solar panels. Now, with warmer and brighter days ahead, it\u2019s time to see if the Philae lander is awake and ready to get back to work. Just don\u2019t expect anything too soon.<\/p>\n
Today, for the first time since it started napping, mission engineers have begun trying to communicate with Philae, which exhausted its batteries soon after landing. After four months, the orbit of the European Space Agency\u2019s Rosetta spacecraft, which has been circling comet 67P, is now aligned with Philae so that they can talk to each other\u2014as long as Philae has eked out enough power and warmth from its limited sunlight. \u201cWe don\u2019t think we\u2019ll hear anything just yet, but we cannot be very sure,\u201d says Koen Geurts, the technical manager of the Philae team.<\/p>\n
Lacking communication with Philae, scientists still don\u2019t know exactly where it is and what its surroundings are like. Engineers have used Rosetta\u2019s cameras to narrow down its location, but the orbiting spacecraft is currently too far away to spot the lander. Rosetta will swoop in closer in July, but as of now, engineers can only estimate that Philae is only getting 1.3 hours of sunlight for each 12.4-hour day on the comet. For the lander to wake up, its solar panels have to be turning those meager hours of sunlight into 5.5 watts of power. And to send and receive signals from Rosetta, it needs 19 watts. Philae also has to be warmer than -49\u02daF to work. \u201cWe do not expect that this is already the case,\u201d Geurts says. \u201cWe think Philae is still cold.\u201d In its shadowy hole, Philae\u2019s temperature may have dropped to as low as -150\u02daF, and even though comet 67P is getting closer to the sun\u2014Philae\u2019s getting twice as much solar energy than it did in November\u2014the spacecraft probably needs more time to thaw.<\/p>\n
But as Philae is still out-of-sight, it could turn out to be in a sunnier place, charged up and ready to go. When or if it wakes up, engineers will take a couple weeks to make sure it\u2019s still working. At least at first, it may be too cold for Philae to fully charge its battery, which will limit how much science it can do. \u201cWithout the battery, science activity can only last as long as sunlight,\u201d Geurts says. That means Philae won\u2019t be able to drill into the icy comet and find out exactly what it\u2019s made of. But it should still be able to do lower-intensity jobs like take pictures, measure the comet\u2019s magnetic field and seismic activity, and sniff the surrounding gases.<\/p>\n
Now that Rosetta and Philae have open lines of communication, mission controllers have commanded the orbiter to start sending signals to Philae starting at 12:00 am EDT. They\u2019ll continue trying to contact Philae until March 20, when Rosetta\u2019s changing orbit puts it out of position. \u201cIf we don\u2019t hear anything in this opportunity, then we hope for the next one,\u201d Geurts says. That next window of opportunity will come between April 13 and 20. If nothing then, several shorter windows open in May, and a longer period opens in June.<\/p>\n
On August 13, the comet will reach its closest point to the sun\u2014and if the European Space Agency hasn\u2019t heard from it by then, they\u2019ll call it quits. With increasing sunlight, ice will sublimate into gas, creating jets and gassy gusts that can knock Philae out.<\/p>\n