Philae May Have Hit a Crater Rim

Scientists are still trying to determine what happened to the Philae lander after it initially touched down on Comet 67P on November 12.   New findings suggest that it may have hit the rim of a crater with one of its landing legs and tumbled before landing again, making one more bounce, and reaching its final resting spot.

Philae (pronounced fee-LAY) traveled for 10 years attached to the European Space Agency’s Rosetta spacecraft.  The pair arrived at Comet 67P/Churyumov-Gerasimenko in August.  Philae separated from Rosetta on November 12 and spent 7 hours floating down to the comet’s surface.  The plan was that harpoons would fire once its landing legs touched the surface to hold the lander in place since comets have almost no gravity.  They did not fire, however, and the lander bounced, flying off into the air for almost two hours before a second bounce and final landing.

Data from the Rosetta Landing Magnetometer and Plasma Monitor (ROMAP), one of 10 instruments on Philae, are being analyzed and used to reconstruct what happened to the lander after the first touchdown, which occurred at 15:34:04 GMT.  After about 40 minutes, at 16:20 GMT, ROMAP data suggest that one leg of the lander hit something, possibly the rim of a crater.  “It was not a touchdown like the first one” according to Hans-Ulrich Auster from the Technische Universität Braunschweig in Germany, ROMAP’s co-principal investigator, who was quoted in an ESA press release today.

Philae had been spinning at about one rotation every 13 seconds before that event.  “After that the lander was tumbling,” Auster continued.  “We did not see a simple rotation around the lander’s z-axis anymore, it was a much more complex motion….”   At 17:25:26 GMT, it touched down on the surface with all three legs for a second time, and at 17:31:17 GMT landed for a third and final time.

ESA and the Rosetta/Philae team still do not know where Philae finally came to rest.   Rosetta will continue to orbit Comet 67P as it travels in toward the Sun and cameras aboard Rosetta are looking for Philae, though it is very small (about one meter — three feet — on each side) and is next to or under a cliff or other surface feature that prevents sunlight from reaching its solar panels to recharge the batteries.  ESA still hopes that as the comet gets closer to the Sun, the lighting conditions may improve for Philae and it could resume its scientific tasks.