This HiRISE image shows a section of Arcadia Planitia, part of the northern plains of Mars. The plains are extremely smooth at large scale. As seen here, they are knobby and rough up close. The surface texture is likely related to several processes involving subsurface ground ice.

Sublimation (a direct transition from ice to gas, without melting to form liquid water) may be partly responsible; large parts of the Martian mid-latitudes have been mantled with a layer believed to be icy dust. This ice is now being lost in the current dry climate causing the ground to collapse slightly, leaving behind a knobby surface.

Another indication of icy ground is the array of cracks found in several parts of the image. These cracks are due to seasonal thermal contraction of frozen ground, creating stresses that fracture the surface. The cracks can form geometric patterns that interact with topography. Such fracture patterns are one of the most common landform in permafrost on Earth. There are also a few large, enigmatic mounds which may be ice-related; these are currently being studied by the HiRISE team.



Written by: Colin Dundas  (20 June 2007)