Eroding Dunes in Chasma Boreale
NASA/JPL-Caltech/UArizona
Eroding Dunes in Chasma Boreale
PSP_009114_2645  Science Theme: Polar Geology
Sand moves along a planetary surface by a process scientists call “saltation,” whereby the individual grains are driven by the wind and bounce forward in short hops. In a process that is not yet completely understood, sheets of saltating sand grains organize themselves into sand dunes, visible in this image as the dark features.

Sand dunes move by having the wind push sand grains up and over the top of the dune where they then slide down to the base. The steep side of the dune that the sand grains slide down is called the slip-face and it is the constant transport of sand from the downwind side of the dune to the slip-face that makes the dune move forward in this direction. HiRISE data allow us to see which side of these dunes has the steeper slope (the slip-face), telling us what direction the dune—and strong near surface winds—are moving (in this case the slip-faces point almost directly to the left).

Yet something else is also happening to these particular dunes. Dark streaks lead away from the dunes toward the lower left of the image. These streaks are caused by sand grains being blown off the dunes and saltating away. This is not ordinarily a cause for concern because in a stable dune, individual grains are constantly added and removed; however, there does not appear to be any influx of sand upwind of these dunes, so they are probably being eroded.

It is also interesting that these streaks do not point in the same direction as the slip-face. One possible scenario is that the dunes migrated westward when sand supply was more plentiful. Today, the wind direction has shifted, blowing more toward the southwest, and the influx of new sand has ceased, such that in the future, the dunes will completely erode away. Repeated HiRISE observations will be able to look for changes in the shape and size of these dunes.



Written by: Shane Byrne  (20 August 2008)
 
Acquisition date
06 July 2008

Local Mars time
12:46

Latitude (centered)
84.663°

Longitude (East)
325.568°

Spacecraft altitude
320.1 km (198.9 miles)

Original image scale range
64.8 cm/pixel (with 2 x 2 binning) so objects ~194 cm across are resolved

Map projected scale
50 cm/pixel

Map projection
Polarstereographic

Emission angle
8.7°

Phase angle
66.7°

Solar incidence angle
60°, with the Sun about 30° above the horizon

Solar longitude
95.1°, Northern Summer

For non-map projected images
North azimuth:  129°
Sub-solar azimuth:  320.8°
JPEG
Black and white
map projected  non-map

IRB color
map projected  non-map

Merged IRB
map projected

Merged RGB
map projected

RGB color
non-map projected

JP2
Black and white
map-projected   (397MB)

IRB color
map-projected   (201MB)

JP2 EXTRAS
Black and white
map-projected  (166MB)
non-map           (180MB)

IRB color
map projected  (60MB)
non-map           (151MB)

Merged IRB
map projected  (390MB)

Merged RGB
map-projected  (365MB)

RGB color
non map           (144MB)
ADDITIONAL INFORMATION
B&W label
Color label
Merged IRB label
Merged RGB label
EDR products
HiView

NB
IRB: infrared-red-blue
RGB: red-green-blue
About color products (PDF)

Black & white is 5 km across; enhanced color about 1 km
For scale, use JPEG/JP2 black & white map-projected images

USAGE POLICY
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-Caltech/UArizona

POSTSCRIPT
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.