Scientists studying data from ESA's Mars Express spacecraft say they may have spotted signs of water on the planet's surface.
Earlier this year, the spacecraft observed the 120-kilometer-wide Hadley Crater, providing images of multiple subsequent impacts from asteroids or comets within the main crater wall, later filled with lava and sediments.
Some of these later impacts reach depths of up to 2600 meters below the surrounding surface. Some have also been partly buried.
The crater also appears to have been eroded by a process known as mass wasting, whereby surface material moves down a slope under the force of gravity.
Mass wasting can be kicked off by a range of processes, including earthquakes, erosion at the base of the slope, ice splitting the rocks or water being introduced into the slope material.
There's no clear indication yet as to which of these processes caused the mass wasting in Hadley Crater, or when. But an examination of the ejecta of the smaller craters within Hadley show sevidence for volatiles - possibly water ice beneath the surface.
The impact that forms the craters would cause this ice to mix with surrounding materials to form a kind of mud, which would then spread over the surface as ejecta.
Scientists believe these volatiles, excavated by the impacts, could indicate the presence of ice to a depth of around hundreds of meters - the difference in depth between the surface and the bottoms of the two craters.