A Large, Longitudinal Dune
A Large, Longitudinal Dune
ESP_039568_1120  Science Theme: Aeolian Processes
Taken in late southern spring and when Mars is near perihelion (closest distance to the Sun), this image shows the effects of dry ice sublimation on a longitudinal dune in the far Southern hemisphere. The bright patches on the dune are still covered in frost, and the dark regions are frost-free.

Longitudinal dunes form when the wind switches between two common directions*. Based on the direction of this dune’s long crest and the orientation of the smaller ripples, it appears the wind blows from the east and from the northwest. However, it would require taking multiple HiRISE images of this location over time and noticing movement before we could say this definitively.

The broad base of this dune may indicate that dune sand has spilled out from areas once covered in ice.

During the next Martian Southern Hemisphere winter (about half a Mars year or one Earth year from when this image was taken in 2015), this dune will again be covered in frost and possibly solid carbon dioxide ice, unable to blow in the wind until the volatiles begin to sublimate in the spring.

*These are ripples indicating a wind out of the north/northwest. The scene is 250 meters across.

Written by: Kirby Runyon (narration: Tre Gibbs)  (11 February 2015)
Acquisition date
04 January 2015

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
247.6 km (153.9 miles)

Original image scale range
25.1 cm/pixel (with 1 x 1 binning) so objects ~75 cm across are resolved

Map projected scale
25 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
53°, with the Sun about 37° above the horizon

Solar longitude
265.8°, Northern Autumn

For non-map projected images
North azimuth:  100°
Sub-solar azimuth:  34.6°
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Black & white is 5 km across; enhanced color about 1 km
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All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible:
NASA/JPL/University of Arizona

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.