Two Generations of Windblown Sediments on Mars
This colorful scene is situated in the Noctis Labyrinthus region of Mars,
perched high on the Tharsis rise in the upper reaches of the Valles Marineris
canyon system.
Targeting the bright rimmed bedrock knobs, the image also captures the
interaction of two distinct types of windblown sediments. Surrounding the
bedrock knobs is a network of pale reddish ridges with a complex interlinked
morphology. These pale ridges resemble the simpler “transverse aeolian ridges”
(called TARs) that are common in the equatorial regions of Mars.
The TARs are still poorly understood, and are variously ascribed to dunes
produced by reversing winds, coarse grained ripples, or indurated dust deposits.
HiRISE observations of TARs have so far shown that these bedforms are stable
over time, suggesting either that they form slowly over much longer time scales
than the duration of MRO's mission, or that they formed in the past during
periods of very different atmospheric conditions than the present.
Dark sand dunes comprise the second type of windblown sediment visible in
this image. The dark sand dune seen just below the center of the cutout displays
features that are common to active sand dunes observed by HiRISE elsewhere on
Mars, including sets of small ripples crisscrossing the top of the dune. In many
cases, it is the motion of these smaller ripples that drives the advance of
Martian sand dunes. The dark dunes are made up of grains composed of iron-rich
minerals derived from volcanic rocks on Mars, unlike the pale quartz-rich dunes
typical of Earth.
This image clearly shows the dark sand situated on top of the pale TAR
network, indicating that the sand dunes are younger than the TARs. Moreover, the
fresh appearance of the sand dunes suggest that they are currently active, and
may help shape the unusual TAR morphology by sandblasting the TARs in the
present day environment.
The original image was acquired on Aug. 31, 2013, by the HiRISE (High
Resolution Imaging Science Experiment) instrument aboard NASA's Mars
Reconnaissance Orbiter (MRO). HiRISE is operated by the University of Arizona,
Tucson.
Caption Credit: Paul Geissler
Image Credit: NASA/JPL/University of Arizona
Image Credit: NASA/JPL/University of Arizona
NASA
Guillermo Gonzalo Sánchez Achutegui
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