Evolution of the South Polar Seasonal Cap
NASA/JPL-Caltech/UArizona
Evolution of the South Polar Seasonal Cap
ESP_021454_0925  Science Theme: Seasonal Processes
This is the first HiRISE image taken after solar conjunction (2010), when Mars passes behind the Sun as seen from Earth. The solar corona interferes with radio communication with MRO for a few weeks during conjunction, so no HiRISE imaging was planned until reliable communication resumed.

This image is one of a set of images taken to monitor the evolution of the South Polar seasonal cap. The seasonal caps on Mars are mostly composed of carbon dioxide, the major component of the Martian atmosphere. It is currently spring in the southern hemisphere of Mars, so the cap is warming and evaporating into the atmosphere by sublimation (going directly from solid to gas). The dark streaks in this image are thought to be sand ejected onto the surface of the cap by jets of carbon dioxide. It is thought that sunlight penetrates to the base of the seasonal cap, warming the soil at its base. This in turn warms the cap from below, causing carbon dioxide to evaporate and build pressure until the gas escapes through vents to the surface. Sand grains are apparently entrained in this flow and deposited in fans on the surface. The brighter streaks may be formed by recondensation of ice on the surface of the cap.



Written by: Ken Herkenhoff  (9 March 2011)
 
Acquisition date
23 February 2011

Local Mars time
21:05

Latitude (centered)
-87.303°

Longitude (East)
167.998°

Spacecraft altitude
246.5 km (153.2 miles)

Original image scale range
24.7 cm/pixel (with 1 x 1 binning) so objects ~74 cm across are resolved

Map projected scale
25 cm/pixel

Map projection
Polarstereographic

Emission angle
0.4°

Phase angle
70.2°

Solar incidence angle
70°, with the Sun about 20° above the horizon

Solar longitude
242.0°, Northern Autumn

For non-map projected images
North azimuth:  234°
Sub-solar azimuth:  38.9°
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HiView

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Black & white is 5 km across; enhanced color about 1 km
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All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible:
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POSTSCRIPT
NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.