Space Briefs
Generations
of windblown
sediments
on Mars
By Paul Geissler
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.
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