Growing Pits in the South Polar Ice Cap
Growing Pits in the South Polar Ice Cap
PSP_004053_0940  Science Theme: Climate Change
This image shows a portion of the South polar permanent ice cap on Mars, which is composed of frozen carbon dioxide (dry ice). This slab of dry ice is a few meters (10-20 feet) thick and is peppered with quasi-circular pits.

The ice is very volatile in comparison to frozen water; it sublimates (evaporates directly from solid to gas) forming carbon dioxide gas when it's exposed to enough sunlight. The ice in this ice cap persists from year to year, yet observations by previous spacecraft have shown that the walls of the pits in this image are retreating by about 3 meters (10 feet) per year, eating away the slab of dry ice. These walls retreat rapidly because they are steeply sloping and absorb much more sunlight than adjacent flat surfaces (which show no changes).

This image is typical of surfaces in the South polar cap. The floors of these pits have only a thin covering of carbon dioxide ice, but the dry-ice mesasóthe adjacent flat-topped plateausóbetween the pits are a few meters thick. The upper surfaces of these mesas are covered in a network of ridges where previous cameras could not observe and may even be accumulating fresh ice each year. This landscape is changing rapidly, so it is thought to be very geologically young; the layers visible in the pit walls probably record variations in the Martian climate over the last few decades.

Written by: Shane Byrne  (20 June 2007)
Acquisition date
08 June 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
247.0 km (153.5 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

Emission angle

Phase angle

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

Solar longitude
253.4°, Northern Autumn

For non-map projected images
North azimuth:  130°
Sub-solar azimuth:  40.3°
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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.