Note: The initial take of this story was published before Philae lost power. It's been updated with details at the bottom, and the subheadline and caption above have been changed to reflect that update.
The European Space Agency isn't sure exactly where Philae, the Rosetta mission's comet lander, is. It's a strange position to be in. We know Philae initially touched down on the comet where it was supposed to, but it then bounced back out into space, touched down again, bounced a little bit and came to rest at an unknown location. The bad news here is that Philae is sitting in much more shadow than expected, keeping its critical solar panels from recharging the batteries as needed.
The ESA is trying to hunt down Philae's location using data collected by the lander as well as imagery gathered by Rosetta from above. With the threat of battery failure looming, plucky Philae is doing all it can to gather data on Comet 67P/Churyumov-Gerasimenko. The Rosetta team activated some of Philae's instruments, one of which is designed to inspect the elemental composition of the comet.
Perhaps the most exciting command from Earth was for Philae to drill into the comet's surface, with the ESA reporting that the instrument is working well. The sample collected by the drill is fed into a device that looks for organic compounds and inspects the molecular makeup of the material. There is some uncertainty as to whether the lander has enough juice to complete this scientific sequence and relay the data back to Rosetta to forward back to Earth. This question will be resolved later today when Philae is expected to report back in. (See update note at end of story.)
Originally, Philae was meant to touch down on the comet and then fire harpoons into the surface to anchor itself into place. That process didn't go as planned. Considering the comet's weak gravitational field, firing the harpoons now could accidentally push the lander back out into space.
Philae has its own Twitter account, with a personality that comes across like an excited puppy. There are lots of exclamation points in its tweets. One recent tweet announced to its followers: "In the end, I won't be firing my harpoons, just in case. Safety comes first! #CometLanding."
Regardless of what fate waits in store for Philae, the mission has been successful on many levels. This is the first time humans have landed a craft on a comet, a process that took an epic 10 years to achieve thanks to the distance Rosetta had to travel to get there. The data collected in the short time that both Rosetta and Philae have been in attendance on the comet will keep scientists busy for years.
The battery situation is worrisome, but that doesn't mean this is the end for Philae. "Even if its current location does not offer optimal exposure to sunlight to fully recharge the secondary batteries," says the ESA, "it is possible that, as the comet approaches to the sun, the illumination will increase and Philae will once more wake up and talk to us."
Updates, 4:40 and 5:18 p.m. PT: This afternoon Philae tweeted, "I confirm that my @RosettaSD2 went all the way DOWN and UP again!! First comet drilling is a fact! :)" Alas, still later the little spacecraft tweeted a sad image that showed how its battery was almost empty (see below) and then later added, in another tweet, "I will use all my remaining energy to 'communicate' between @ESA_Rosetta and myself with @ConsertRosetta." Finally, Philae and Rosetta exchanged tweets suggesting that the data from the drilling experiment had been safely shuttled to Rosetta, and then Philae sent Rosetta an optimistic tweet before slipping into sleep: "My #lifeonacomet has just begun @ESA_Rosetta. I'll tell you more about my new home, comet #67P soon... zzzzz"