Bright Dust Devil Tracks over RSL in Eos Chasma
NASA/JPL/UArizona
Bright Dust Devil Tracks over RSL in Eos Chasma
ESP_062917_1640  Science Theme: Composition and Photometry
This image (see cutout) features large candidate recurring slope lineae (RSL), which some have considered evidence for seeping water. They are “candidate” RSL because we have not seen them change over time in ways that definitely identify them as RSL

Recent research has favored dry models for RSL formation, in which the darkening is due to removal of bright dust. There are often dark dust devil tracks associated with RSL sites, supporting this interpretation. At this site, however, we see bright dust devil tracks where they cross the RSL. The dust devil tracks are the diffuse streaks that cross the topography at various angles, not following the downhill direction. How can dust devil tracks be bright from dust removal or redistribution while RSL are dark from dust removal?

The answer may be that the grain size and roughness of the surface is changing. Small grains and smoother surfaces tend to be brighter than coarser-grained or rougher surfaces. Bright dust devil tracks are seen elsewhere on Mars, and one example on Earth in which the passing dust devil produces a smoother surface. Downhill is to the upper left of this cutout image, and the dark RSL flow directly down the slope gradient.

Written by: Alfred McEwen  (25 February 2020)
 
Acquisition date
28 December 2019

Local Mars time
15:27

Latitude (centered)
-15.769°

Longitude (East)
315.152°

Spacecraft altitude
264.6 km (164.4 miles)

Original image scale range
53.9 cm/pixel (with 2 x 2 binning) so objects ~162 cm across are resolved

Map projected scale
50 cm/pixel and North is up

Map projection
Equirectangular

Emission angle
11.3°

Phase angle
71.1°

Solar incidence angle
62°, with the Sun about 28° above the horizon

Solar longitude
127.4°, Northern Summer

For non-map projected images
North azimuth:  97°
Sub-solar azimuth:  40.1°
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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.