Matthew Chojnacki wrote:Sand Dune Catch and Release (ESP_034084_1655) (HiClip)
Sand dunes on Mars are frequently found within craters, raising the question: do they form from sandy materials within the craters, or are they simply traps for dunes traveling in their path?
This image shows dozens of dark-toned dunes in and around several craters within the rugged terrain of Terra Cimmeria. Based on the positions of the dune avalanche slopes, called "slip faces", the migration direction is toward the bottom of the image (to the south).
This direction relative to the local terrain indicates that the dunes here have been transported in and out of the craters on their path southward. Smaller sand patches appear anchored in the depressions where wind cannot effectively initiate sand motion, trapping sand indefinitely.
Here, HiRISE has revealed sand dunes can be both be caught and released by craters on Mars.
HIRISE Science Team wrote:Waiting for Dust Devils (ESP_036376_2160) (HiClip)
HiRISE has captured some stunning images of dust devils in action, but the overall sample remains fairly limited. Both Mars Orbiter Camera and HiRISE images in this general region have a fairly high rate of capturing dust devils (sometimes several in one image), so acquiring images here in the right season has a good chance to help us obtain better measurements of these features.
This image has been fairly successful, showing one well-defined, large dust devil in the north and two less well formed ones in the center. Dust devils are identified in images both by their cloudy form and the shadow their cloud casts on the surface, from which the height of the dust devil can be determined.
Dust devils on Mars form the same way they do in deserts on Earth: strong heating of the surface by the sun, rising of heated, less-dense air that swirls upwards in a column, some wind to move it along a path over the ground, and entrainment, or picking up, of surface particles such as dust.
Preliminary results have shown that the along-ground movement and the circulating winds of a dust devil can be estimated using the HiRISE color frames if the dust devils happen to be imaged in the HiRISE color swath (down the center of the image).
HiRISE Science Team wrote:Moving Mass Material on a Mesa (ESP_036382_2255) (HiClip)
This image appears to show some type of mass movement of material down the wall of a mesa in Deuteronilus Mensae. Also visible is an arc-shaped ridge at the end of the valley.
The ridge may be a moraine from a glacier. HiRISE may be able to see that the surface of the moraine is coarser than the material in front of the ridge.
Colin Dundas wrote:Blockfall on the North Polar Layered Deposits (ESP_036436_2645) (HiClip)
The North Polar layered deposits (NPLD) are a stack of layers of ice and dust at the North Pole of Mars. The layers are thought to have been deposited over millions of years, as the atmosphere changed in response to the varying tilt of the planet’s axis. Learning to read this record could tell us much about recent conditions on Mars, but we first need to understand the processes that have shaped the NPLD.
Comparing this HiRISE image with an observation from the previous Martian year reveals an example of one of these processes: block falls. The slope is steep and fractured here, and a large chunk of dusty ice has tumbled down the slope and broken apart. Scientists on the HiRISE team are studying this process at many locations in order to measure how quickly the NPLD is changing.
Other changes are visible on the slope as well: sand patches have shifted, and in some places on the slope they have been eroded into grooves or troughs, most likely by the carbon dioxide frost (dry ice) that covers the North Pole in the winter.
Credit: NASA/JPL/University of Arizona
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