Dust Devil East of Hellas Planitia
18 Jul 2007
(Source: Jet Propulsion Laboratory/University of Arizona)
This image is of a region east of the Hellas impact basin and south of Reull Vallis. Unexpectedly, Mars Reconnaissance Orbiter's HiRISE instrument caught a dust devil blowing across the Martian surface in the southwest portion of the image.
Dust devils form when the temperature of the atmosphere near the ground is much warmer than that above. The hot air rises, and under ideal conditions, forms a vortex that sucks in more warm air. If the vortex is strong enough, it will raise dust off the surface, forming a dust devil.
Dust devils generally form in the afternoon because the sunlight needs sufficient time to warm the surface. When this image was taken, the local time was about 3:08 p.m.
The bright material is the dust within the vortex, and a dark shadow cast by the dust devil is visible to the right. The diameter of this dust devil is about 200 meters, but at the surface it is probably much smaller. Based on the length of the shadow in this image, the dust devil is on the order of 500 meters tall.
More image sizes are available from the University of Arizona's HiRISE site: http://hirise.lpl.arizona.edu/PSP_004285_1375