Mercury 'hollow' up close
Mercury's "hollows" are seen all over the planet and are one of the Messenger mission's great discoveries.
Scientists believe they are created by the ground slumping as a result of the release of volatile material evaporating away into space.
Mission scientists have been surprised at quite how much volatile material is retained in Mercury's surface.
Video courtesy of Nasa.
16 Feb 2013
- From the section Science & Environment