Scientists working with the Rosetta mission have discovered astonishingly deep sinkholes on Comet 67P/Churyumov-Gerasimenko, deeper than they are wide, which is especially amazing considering how big they are compared to the comet itself. Poring over imagery taken over the last seven months, they’ve demonstrated that jets are emerging from these sinkholes. Tentatively, the formation model they have for the sinkholes is that the interior of the comet is probably spongy, with lots of voids, and periodically enough of the surface sublimates away above a void that the thin remaining crust can no longer support itself and falls in. This exposes the interior of the void to space and the heat of the Sun and it begins to sublimate, accelerating the formation of the sinkhole. What’s really interesting is that the sinkholes aren’t uniformly distributed around the comet, which may reveal clues to the uneven interior structure and composition of the comet.
And, of course, they’ve got some excellent pictures (click for full size):