Last updated on April 18, 2014 at 15:29 EDT
Field of Fans  PSP0025320935 Subimage 2
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Field of Fans (PSP_002532_0935) Subimage 2

December 26, 2007
At the very beginning of spring in the southern hemisphere on Mars the ground is covered with a seasonal layer of carbon dioxide ice. In this image there are two lanes of undisturbed ice bordered by two lanes peppered with fans of dark dust.

When we zoom in to the subimage, the fans are seen to be pointed in the same direction, dust carried along by the prevailing wind. The fans seem to emanate from spider-like features.

The second subimage zooms in to full HiRISE resolution to reveal the nature of the "spiders." The arms are channels carved in the surface, blanketed by the seasonl carbon dioxide ice. The seasonal ice, warmed from below, evaporates and the gas is carried along the channels. Wherever a weak spot is found the gas vents to the top of the seasonal ice, carrying along dust from below.

The anaglyph of this spider shows that these channels are deep, deepening and widening as they converge. Spiders like this are often draped over the local topography and often channels get larger as they go uphill. This is consistent with a gas eroding the channels.

A different channel morphology is apparent in the lanes not showing fans. In these regions the channels are dense, more like lace, and are not radially organized. The third subimage shows an example of "lace."