Sources of Basaltic Sand
Sources of Basaltic Sand
PSP_006528_1120  Science Theme: Aeolian Processes
Sand dunes are among the most prominent wind-formed features found on Mars. Their shapes depend on the winds and also on the local supply of sand grains, so they provide clues to the nature of both the Martian atmosphere and surface.

Dunes form through the accumulation of coarse sand grains carried by the wind by means of saltation, or bouncing along the surface. Monitoring the present day dune activity can help determine the timescale over which Martian rocks are eroded, as the impacting grains sandblast the surface over time. The sands of Mars must be continually replenished as the coarse grains are ground into fine dust by repeated impacts. Finding the hidden sources of fresh sand is a challenge for HiRISE.

This image was targeted at a point in Mitchell Crater in the southern highlands of Mars where sands abruptly appear and spread north. The sands seem to derive from the edge of an eroding mesa (shown here with an arrow. Nearby terrain suggests that boulders and sand have been excavated by erosion from beneath brighter, polygonally fractured ground.

This rocky layer may originally have been a lava flow; Martian lava flows are predominantly composed of basalt, which would account for the dark color of the sand. The polygonal pattern of the bright upper layer may be due to repeated freezing and thawing of the soil that buries the lava flow. The tracks of dust-devils are clearly visible on the smooth, sandy surface but largely vanish when they cross into the polygonally fractured terrain.

Written by: Circe Verba and Paul Geissler  (30 January 2008)
Acquisition date
18 December 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
248.1 km (154.2 miles)

Original image scale range
49.6 cm/pixel (with 2 x 2 binning) so objects ~149 cm across are resolved

Map projected scale
50 cm/pixel

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Phase angle

Solar incidence angle
76°, with the Sun about 14° above the horizon

Solar longitude
4.2°, Northern Spring

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North azimuth:  99°
Sub-solar azimuth:  53.4°
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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.