Every winter Mars' polar region is covered with a layer of seasonal carbon
dioxide ice (dry ice). In the spring jets of gas carry dust from the
ground up through openings in the ice. The dust gets carried downwind by
the prevailing wind and falls on top of the seasonal ice layer in a
fan-shaped deposit. Many jets appear to be active at the same time since
numerous fans are all deposited in the same direction.
This image from the High Resolution Imaging Science Experiment (HiRISE)
camera on NASA's Mars Reconnaissance Orbiter appears to show several times
at which jets were active. At the top of this image the fans are oriented
in one direction while at the bottom they are going in a different
direction. This suggests that as the ice layer thins, a set of gas jets
becomes active, they die down, then further away another set starts up at
a later time with a different prevailing wind direction.
This is a reduced-resolution image from the HiRISE Observation observation
catalogued as ESP_011934_0945, taken on Feb. 11, 2009. The observation is
centered at 85.4 degrees south latitude, 104.0 degrees east longitude.
The image was taken at a local Mars time of 6:12 p.m.and the scene is
illuminated from the west with a solar incidence angle of 79 degrees, thus
the sun was about 11 degrees above the horizon. At a solar longitude of
207.9 degrees, the season on Mars is northern autumn.
NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for
NASA's Science Mission Directorate, Washington. Lockheed Martin Space
Systems, Denver, is the prime contractor for the project and built the
spacecraft. The High Resolution Imaging Science Experiment is operated by
the University of Arizona, Tucson, and the instrument was built by Ball
Aerospace & Technologies Corp., Boulder, Colo.