Mars Global Surveyor imaged Mars from 1997‐2006, and observed nineteen spots in dust-covered regions that darkened at various times, and that correspond to very recent-looking impact craters.

The craters are much smaller than the dark spots; the darkening is thought to be due to an atmospheric blast or high winds associated with the event which removed or redistributed the bright dust.

HiRISE has been re-imaging these locations, revealing many new details. In several locations the dark spots contain many dark streaks on topographic slopes. These dark streaks trend downhill, and the images reveal that a thin surface layer has been removed. These are interpreted as dust avalanches, which are common over dusty slopes of Mars.The dark streaks mark the most recent avalanches, which are often only a few years or decades old.

Visible here in the dark region is the densest concentration of dark streaks ever seen on Mars. Possibly these dust avalanches were triggered by the impact event, either from the atmospheric blast or from seismic shaking when the asteroid fragments struck the ground.



Written by: Alfred McEwen  (4 June 2007)