Asteroid, can learn a lot from philae’s bumpy landing

The hardness of the comet surface will be a key piece of knowledge for future small body landings. Prior to landing, scientists didn’t know whether to expect a snow-like surface in which Philae might sink or a hard, icy one on which it might bounce. (Comets and asteroids are both small bodies, with asteroids generally rockier and comets icier. However, the line between the two has blurred with the discovery of bodies like Wilson–Harrington, a comet that lost its tail, turned black, and was then “rediscovered” as asteroids.) “We proved that bouncing is the major problem, though we didn’t want
to do that,” says Philae landing manager Stephan Ulamec, alluding Philae originally had three ways to counteract the comet’s low gravity: a damping mechanism, a cold gas thrust system pushing down, and anchoring harpoons. Only the damping mechanism worked, and it obviously wasn’t enough. Future landings, says Ulamec, would likely also need redundant systems, and more testing is necessary to ensure parts like the nitrocellulose powering the harpoons can withstand the environment of space. The upside of the bouncing is that the Rosetta team was able to test the hardness of both Philae’s initial and final landing spots, which had a 2,000 fold difference.