South Polar Residual Cap
NASA/JPL/University of Arizona
South Polar Residual Cap
PSP_004000_0945  Science Theme: Climate Change
twitter  •  tumblr

WALLPAPER
800
1024
1152



Like Earth, Mars has concentrations of water ice at both poles. Because Mars is so much colder, however, the seasonal ice that is deposited at high latitudes in the winter and is removed in the spring (generally analogous to winter time snow on Earth) is carbon dioxide ice. Around the south pole there are areas of this carbon dioxide ice that do not disappear every spring, but rather survive winter after winter&emdash;this persistent carbon dioxide ice is called the south pole residual cap.

Relatively high-standing smooth material is broken up by circular, oval, and blob-shaped depressions, forming a pattern called "swiss cheese" terrain. The high-standing areas are carbon dioxide ice with thicknesses probably of several meters. The depressions are thought to be caused by the removal of carbon dioxide ice by sublimation (the change of a material from solid directly to gas). By looking at different sized depressions in an image such as this, and by comparing images of the same place from year to year, the development of "swiss cheese" terrain can be observed.

The sublimation process may begin anywhere as a small depression. Once this small depression is formed, it expands laterally in all directions, creating the rounded depressions we see today. As most depressions seem to have a similar depth and have relatively flat bottoms, there is likely some layer below, possibly of water ice, that cannot be as easily removed by sublimation. Thus, while the south polar residual cap as a whole is present every year, there are certainly annual changes taking place within it.

Especially apparent and interesting in this image are the strips of material that parallel the edges of many depressions. Often there are two or more concentric strips that are smooth like the surrounding surface, but seem to be lower than the surrounding surface and in places appear to be tilted down towards the center of the depression. Inner strips are sometimes broken up into chunks. It may be that the uppermost smooth layer is a bit more resistant to sublimation than the material just below it&emdash;the quicker removal of the underlying material might cause the stronger upper layer to detach from the surrounding terrain and settle down towards the center of the depression.

Alternatively, these ringing strips may indicate that many layers are present within the carbon dioxide ice. Another interesting feature is the faint crisscrossing network of ridges on the upper smooth terrain. These may also be complexly involved in the sublimation and deposition of carbon dioxide ice.

With the high resolution capability of HiRISE, we intend to measure the amount of expansion of the depressions over one or more Mars years. Knowing the amount of carbon dioxide removed can give us an idea of the current atmospheric and climate conditions, and possibly how Mars climate may be changing. Written by: Patrick Russell  (1 August 2007)
 
Acquisition date
04 June 2007

Local Mars time
17:36

Latitude (centered)
-85.649°

Longitude (East)
6.276°

Spacecraft altitude
247.7 km (154.0 miles)

Original image scale range
24.8 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
0.6°

Phase angle
66.4°

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

Solar longitude
250.8°, Northern Autumn

For non-map projected images
North azimuth:  126°
Sub-solar azimuth:  39.5°
JPEG
Black and white
map projected  non-map

IRB color
map projected  non-map

Merged IRB
map projected

Merged RGB
map projected

RGB color
non-map projected

JP2
Black and white
map-projected   (264MB)

IRB color
map-projected   (141MB)

JP2 EXTRAS
Black and white
map-projected  (103MB)
non-map           (111MB)

IRB color
map projected  (24MB)
non-map           (125MB)

Merged IRB
map projected  (56MB)

Merged RGB
map-projected  (52MB)

RGB color
non map           (109MB)
ADDITIONAL INFORMATION
B&W label
Color label
Merged IRB label
Merged RGB label
EDR products
HiView

NB
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

USAGE POLICY
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

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.