Icy Impact
Icy Impact
ESP_014436_0920  Science Theme: Polar Geology
A thick (approximately 3 kilometer or about 2 mile) sequence of ice and dust, stacked like a layer cake, covers the south pole of Mars. Impact craters that form here experience slightly different processes of modification and degradation than those that form in rocky areas.

One example of such a process is sublimation. Most of the material that makes up an icy crater is volatile, meaning it can melt or sublimate (change directly from a solid to a gas) if heated. Sublimation is more common on Mars because of its thin, dry atmosphere. Crater walls facing the Sun receive more direct light than their surroundings, and are therefore more easily warmed. If the ice in the walls sublimates, the rim structure of the crater becomes degraded.

The impact crater in this image is roughly 900 meters (a little over 0.5 mile) across. The remaining raised rim of the crater is illuminated from the bottom right of the image, causing preferential heating of the interior of the rim structure. The ice appears thin here (more brown material is exposed), with an even thinner cover on the remaining exterior rim. This could be caused by a number of possibilities: perhaps the exterior wall is steeper than the interior wall, resulting in more direct exposure to sunlight, causing more efficient sublimation when the Sun shines on that wall.

Once ice begins to melt, darker dustier material is exposed. The darker material absorbs more heat than white ice (just like standing in the Sun wearing a black shirt makes you warmer than wearing a white shirt, which reflects the Sun's light), causing more and more ice to sublimate near the dark material. You can observe this process happening around the exterior crater wall in this HiRISE image.

Written by: Andrea Philippoff  (7 October 2009)
Acquisition date
25 August 2009

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
247.7 km (154.0 miles)

Original image scale range
24.9 cm/pixel (with 1 x 1 binning) so objects ~75 cm across are resolved

Map projected scale
25 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
78°, with the Sun about 12° above the horizon

Solar longitude
327.2°, Northern Winter

For non-map projected images
North azimuth:  175°
Sub-solar azimuth:  54.9°
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

Black and white
map-projected   (495MB)

IRB color
map-projected   (226MB)

Black and white
map-projected  (254MB)
non-map           (332MB)

IRB color
map projected  (101MB)
non-map           (248MB)

Merged IRB
map projected  (140MB)

Merged RGB
map-projected  (129MB)

RGB color
non map           (216MB)
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’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.