Matthew Chojnacki wrote:Dunes and Wind Streaks in Arabia Terra (ESP_037714_1935) (HiClip)
Arabia Terra is one of the more dusty regions on Mars, where ever-falling red dust covers the surface allowing only minor variations in color and tone. One exception is when wind-driven, dark-toned sand moves across the surface ejecting the bright dust into the atmosphere to reveal the dust-free surface below.
This HiRISE image shows sand dunes with surrounding larger tear drop-shaped light streaks pointing west (or, to the left). This orientation, along with the morphology of the local dunes, indicates winds from the east have stripped sand particles off the dunes and carried them downwind to form these light streaks. More importantly, active sand has a role in the slow erosion of the rocks here and the overall landscape evolution of the region.
Paul Geissler wrote:Braided TARs in Syrtis Major (ESP_038227_2020) (HiClip)
Transverse aeolian ridges (TARs) are commonly found throughout the Martian tropics, including rocky regions such as Syrtis Major that are largely devoid of dust.
These bright wind-blown ripples most often occur in simple sets of ridges with regular size and spacing. Typical TARs stand a few meters tall and have a wavelength (that is to say, separation) of 30 to 60 meters. HiRISE has not detected any changes among the TARs today, suggesting that they are inactive.
In this scene, we see TARs with a highly unusual morphology. Instead of single ridges, we see sets of small ridges that are separated by about 50 meters. The smaller ripples are spaced only 5 to 8 meters apart. Between the smaller ripples are even smaller striations that are perpendicular to the ridge crests with regular spacings of less than 2 meters.
This image raises a number of puzzling questions. Why are the ripples organized into two distinct wavelengths? Did the different wavelengths result from different processes or from different conditions? When did these wavelength-specific conditions or processes take place? Did they occur together, or did they alternate, or did one take place after the other? Were the processes depositional or erosional, or both?
The complexity of Martian TARs makes us think twice about any single explanation for their origin.
M. Ramy El-Maarry wrote:An Enigmatic Feature in Athabasca Lava Flows (ESP_038646_1805) (HiClip)
What is this enigmatic landform?
The circular feature is nearly 2 kilometers (1.2 miles) wide. It looks like a circular island surrounded by a "sea" of smooth-looking lava flows. The Athabasca region contains some of the youngest lava flows on Mars. Therefore, it is highly possible that volcanism played a role in creating this feature.
Perhaps lava has intruded underneath this mound and pushed it up from beneath. It looks as if material is missing from the mound, so it is also possible that there was a significant amount of ice in the mound that was driven out by the heat of the lava. There are an array of features like this in the region that continue to puzzle scientists.
We hope that close inspection of this HiRISE image, and others around it, will provide some clues regarding its formation.
Cathy Weitz wrote:Clays along the Coprates Chasma Plateau (ESP_038918_1650) (HiClip)
This image shows exposures of deposits along the plateau just to the south of Coprates Chasma.
Whereas Coprates Chasma and many of the other chasmata of Valles Marineris contain kilometer-thick light-toned mounds made up of sulfates, several of the deposits along the plateau have signatures of clays. This indicates that water was here for extensive periods of time to cause the plains to weather and alter into clays.
Credit: NASA/JPL/University of Arizona
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