Enlarge / The close-ups highlight the bright ice exposed in the boulders when Philae struck them during its second touchdown (green box above). (credit: O'Rourke et al./Nature) The Rosetta mission’s attempt to drop the Philae lander on a comet in 2014 didn’t go according to plan. The harpoon mechanism meant to stick Philae to terra-not-quite-firma didn’t work, and poor Philae ended up bouncing around and landing under a dark cliff overhang, unable to deploy its solar panels and complete its tasks.