We did it! We’re on the comet! At about 9:37 a.m. (CST) Philae touched down on Rosetta’s Comet. After traveling more than 315 million miles (508 million km) the lander’s signal arrived 28 minutes later with the fabulous news. Telemetry is trickling in and the lander’s in great health, but one small concern has arisen. We’ve just learned that the harpoons used to anchor Philae failed to fire. Mission control is considering whether to refire them to make sure the craft is stable.
One might think that as long as the craft is sitting still on the comet, that will do. Well, maybe. Until it’s anchored, activity from nearby jets or even vaporizing ice beneath it could flip it over. After all, Philae only weighs a gram in 67P/C-G’s gravity field. The harpoons also house the instrument that measures surface density. Presumably, without them we won’t get that data.
Now that Philae has reached its target, science will begin in earnest. Here’s an illustration that describes each of the probe’s instruments. Be sure to click to enlarge.