All things come to an end, and with the Philae comet lander, it appears to be coming all too soon. On Thursday, mission leaders had been extremely cautious—wary of using moving parts for fear of upsetting the precarious position of the three-legged robot, which is wedged in and tipped up on its side, in the shadow of a wall of material. But by Friday morning, that precaution had given way to a headlong rush for the European Space Agency (ESA), which just 2 days earlier was celebrating the historic success of the Rosetta mission. Scientists were trying to gather data from all 11 lander instruments before the 60-hour battery expired. The wan 1.5 hours per day of light that strikes the solar panels is not enough to recharge its batteries in a significant way.
So overnight, an x-ray instrument was lowered to the comet, and a hollow rod meant to measure thermal and mechanical properties was hammered into the surface. On Friday morning, the team was uploading commands to drill into the subsurface, in order to feed a sample to two evolved gas experiments—the most complicated and energy-intensive experiments on the lander. During a radio pass planned for Friday night—probably one of the last exchanges of the mission—there was talk of rotating the solar panels into a more favorable position, or even doing something more radical, like hopping with the lander's springy legs and hoping for the best. “We are coming now to the end so we are taking more and more risks,” says Paolo Ferri, the head of mission operations at ESA’s command center here.
Meanwhile, there was another race: finding the lander. On Thursday, Holger Sierks, the principal investigator for the Rosetta orbiter’s main science camera, had hoped to find the lander in an image about 1 kilometer away from the target site. (Before coming to a rest, Philae bounced in a big way.) But as of Friday morning, Ferri did not think that that effort had been fruitful. Part of the problem is that Rosetta has retreated to a 50-kilometer orbit—much too far to spot the lander in current passes overhead. Sierks says Philae would be just a 1-pixel dot at that distance. So instead he is combing pictures taken just after the landing, when the lander would be more of a 3-by-3- pixel smudge. Better results have been coming from the CONSERT instruments, Ferri says. These instruments, one on the orbiter and one on the lander, exchange radio signals to make a tomograph of the comet’s interior (when the comet lies between the lander and the orbiter). But the instruments can also be used like a radar when the orbiter is directly over the lander. Ferri says scientists have already collected one sounding, which traces out a circle of probable location. Two more soundings would pinpoint the lander.
Mark McCaughrean, a senior science adviser at ESA's European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands, says it looks as if Saturday could herald the end of Philae’s primary life. Ferri said there was a good chance for minor resurrections: Philae might occasionally be able to wake up, its batteries slightly refreshed, with further news from a world never before visited. Changes in seasons could bring better light. And on a gas-and-dust-spewing comet—an active body getting ever more active—there is always the possibility for a change in environment: Philae is not the only moving part on comet 67P/Churyumov-Gerasimenko. But even if this was truly the end, Ferri was happy, head to toe. “It’s a clean end. The main mission performed. I’m not sad at all. This is a major success.”
Update: The short life of the Philae comet lander is in all likelihood now over, reports the European Space Agency. Contact with the lander was lost at 1:36 am CET Saturday morning / 6:36 pm ET Friday night, after nearly 57 hours on the surface of comet 67P/Churyumov-Gerasimenko. Philae is now in an 'idle' or hibernation mode. Mission leaders reported having deployed and collected data from all 10 of the lander's science instruments, though it remains to be seen if the complex drilling procedures were able to feed samples into two mass spectrometry experiments. One of the last successful commands to the lander lifted its body 4 centimeters and rotated its solar panels by 35 degress in an effort to position it to collect more sunlight. But it could be days, weeks or months before Philae is ever heard from again.
Earlier update: At a 1 p.m. GMT press conference on Friday, ESA scientists and operations staff discussed Philae’s prospects as they wait to establish contact with the lander later today. “We have activated the drill. Whether it has taken samples, we’ll know that this evening. We don’t know if there is enough battery,” says lander manager Stephan Ulamec of the German space agency (DLR) in Berlin. The next contact with Philae is expected late this evening, European time, but with only 1 hour and 20 minutes of illumination on one of its solar panels, hopes are not high. “It may be dead before we make contact again. We have to be ready for that,” Ulamec says.
Ulamec says that if they manage to get data from the lander this evening, once that is done they may try to rotate the craft slightly so that maybe a slightly larger solar panel will get some light. Another idea being considered, according to Valentina Lommats of DLR, is to raise up the body of the lander in the hope of bouncing out of its current shady situation. “We’re throwing around ideas right now,” she says. Lommats also raised the possibility that, as the comet approaches the sun, the extra illumination may recharge the batteries and allow controllers to reestablish contact. “It looks a bit bad, but we can always hope,” she says.
Among the speakers at the press conference, there was no sense of failure that Philae’s mission is ending so soon. Ulamec says that they have received about 80% of the data they had hoped to get in the first science sequence. Rosetta project scientist Matt Taylor, who's also based at ESTEC, says it has been an “overwhelming experience.” Flight director Andrea Accomazzo says: “It’s unique and it will be unique forever. Let’s not forget that.” Says Ulamec: “Let’s keep our fingers crossed and hope we get a message this evening.”
