When the ESA's Rosetta spacecraft reaches Comet 67P/Churyumov-Gerasimenko, it will send down the Philae lander to the surface. Landing on a comet has never been done, and it's as hard to do as it sounds. The lander will need to be able to deal with any kind of surface, from solid ice to fluffy snow. The comet's gravity is very weak, so the spacecraft could bounce off the surface if it descends too quickly. The lander is equipped with pads that spread its weight over a large area to stop it from sinking into powdery snow. It also has a harpoon that will fire as it gets close to stop the lander from drifting back into space. We'll find out if it works in 2014.