TARs and Unusual Star Ripples
NASA/JPL/University of Arizona
TARs and Unusual Star Ripples
PSP_008323_1735  Science Theme: Aeolian Processes
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This blocky terrain is southwest of Schiaparelli Crater and is surrounded by a field of Transverse Aeolian Ridges (TARs) and unusual star ripples (dunes).

TARs are linear ripples with crest-ridge morphologies that can vary in shape; these morphologies include forked, sinuous, barchanoid, networked or feathered characteristics. The ridges also appear to transition into star dunes.

Star dunes are complex features and are not yet fully understood on Earth. They form by multidirectional wind regimes with a dominant primary wind. Chains of star dunes often appear to have a massive linear appearance, or can be modified linear or barchan dunes with the formation of secondary slipfaces (on the steeper slope). On Earth, there are incipient star dunes, such as in the Dumont dune field in the Mojave Desert, that display similar characteristics. The Dumont embryonic star dunes may result from dunes merging as they overrun one another, or are modified preexisting dunes, which could also be the case in this image.

Martian weather models predict that the dominate wind comes from a southwesterly direction. This direction aligns nicely with the transverse ripples and the main arms of the star ripples. This suggests that the star ripples were also affected by a different wind pattern or secondary winds or airflow. (Secondary airflow is the airflow and sediment transport around the slopes of the dune.)

Formation of incipient star dunes depends on the nature (strength, direction, and duration) of the primary wind and the volume of the sand to create the dune. Secondary airflow maintains the dune arms. The last factor is the deposition or removal of the sand by grainfall or grainflow avalanching. Grainfall and grainflow transports material from the main crestline slipface and along-slope or down-slope which maintains the secondary arm crest.

Written by: Circe Verba  (2 July 2008)
 
Acquisition date
06 May 2008

Local Mars time
15:11

Latitude (centered)
-6.368°

Longitude (East)
11.822°

Spacecraft altitude
266.5 km (165.6 miles)

Original image scale range
26.7 cm/pixel (with 1 x 1 binning) so objects ~80 cm across are resolved

Map projected scale
25 cm/pixel and North is up

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Equirectangular

Emission angle
3.9°

Phase angle
58.4°

Solar incidence angle
55°, with the Sun about 35° above the horizon

Solar longitude
68.0°, Northern Spring

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North azimuth:  97°
Sub-solar azimuth:  39.5°
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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.