Nature: Philae, the cometary lander from the European Space Angeny's Rosetta mission, may never be heard from again, but it has provided a wealth of data already, much of it contrary to expectations. When Philae landed it bounced because the surface was not, as expected, a deep layer of dust. Measurements of the leg compression and from the hammer that was supposed to penetrate the surface have revealed that the comet's surface is a hard crust covered in areas with thin layers of dust and ice. The hard surface could have formed due to reactions with solar radiation and compaction, but regardless of the cause it challenges the assumption that cometary material is essentially unchanged since the formation of the solar system. The presence of complex polymers in the surface material is also likely a recent phenomenon. Philae's cameras revealed a wide range of hard-to-explain surface features. Radio signals used to probe the comet show that the interior has a relatively consistent composition and is much more porous than expected based on the nature of the surface.
