Spider Features in the South Polar Region
Spider Features in the South Polar Region
ESP_013049_0950  Science Theme: Seasonal Processes
This image is part of an ongoing seasonal monitoring effort in this location in the southern polar region of Mars.

Mars' south polar region changes significantly during the Martian year. During the southern hemisphere's winter, the polar cap increases dramatically as the lowered temperatures make a large portion of the atmosphere freeze out into ice. As spring approaches and the polar region begins to warm once again, the cap recedes revealing terrains like those visible in this image.

The polygonal features in this image are termed "spiders" and their origin is still unknown (although there are several hypotheses). One possible hypothesis for the black fan-shaped features is that they may be formed by a geyser-like process. As the sun heats the ground layer below the carbon dioxide ice, the ice on the bottom begins to sublimate, or turn directly from a solid to a gas. This gas then builds up in pressure as more of it sublimates, until a critical pressure is achieved and it erupts through the ice layer much as a geyser would, spewing the debris that is thought to make up the dark fan shaped features.

Written by: Shawn D Hart  (3 June 2009)
Acquisition date
09 May 2009

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
247.1 km (153.6 miles)

Original image scale range
49.4 cm/pixel (with 2 x 2 binning) so objects ~148 cm across are resolved

Map projected scale
50 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
64°, with the Sun about 26° above the horizon

Solar longitude
262.3°, Northern Autumn

For non-map projected images
North azimuth:  122°
Sub-solar azimuth:  41.8°
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B&W label
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Black & white is 5 km across; enhanced color about 1 km
For scale, use JPEG/JP2 black & white map-projected images

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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.