Evolution of the South Polar Residual Cap
Evolution of the South Polar Residual Cap
PSP_004687_0930  Science Theme: 
As on Earth, the seasonal frost caps of Mars grow and recede each year. But seasonal frost on Mars is composed of carbon dioxide ice (also known as dry ice), not water ice as on our planet.

Near the south pole of Mars, the seasonal carbon dioxide frost never completely disappears, leaving a residual ice cap of carbon dioxide ice throughout the summer. This HiRISE image shows part of the south polar residual cap, with many shallow pits dubbed “Swiss cheese” terrain. Because the sun is always low in the sky at this latitude, the steep walls of the pits receive more solar energy than the high-standing, flat areas between the pits. This causes the walls of the pits to retreat several meters per year as sunlight causes the carbon dioxide ice to evaporate directly to gas, a process called “sublimation.”

In some depressions, ridges or blocks of material a couple of meters across are visible at the base of the depression walls, likely fallen from the walls during the sublimation and retreat process. At this rate, the layer of carbon dioxide ice could completely disappear in about 100 years if not replenished.

Written by: Ken Herkenhoff  (4 November 2009)
Acquisition date
27 July 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
245.4 km (152.5 miles)

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

Map projected scale
25 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
66°, with the Sun about 24° above the horizon

Solar longitude
284.5°, Northern Winter

For non-map projected images
North azimuth:  148°
Sub-solar azimuth:  49.2°
Black and white
map projected  non-map

IRB color
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Merged IRB
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Merged RGB
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RGB color
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Black and white
map-projected   (857MB)

IRB color
map-projected   (424MB)

Black and white
map-projected  (518MB)
non-map           (573MB)

IRB color
map projected  (181MB)
non-map           (443MB)

Merged IRB
map projected  (193MB)

Merged RGB
map-projected  (174MB)

RGB color
non map           (377MB)
B&W label
Color label
Merged IRB label
Merged RGB label
EDR products

IRB: infrared-red-blue
RGB: red-green-blue
About color products (PDF)

Black & white is 5 km across; enhanced color about 1 km
For scale, use JPEG/JP2 black & white map-projected images

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:
NASA/JPL/University of Arizona

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.