Ginny Gulick wrote:Multi-Elevation Gullies (ESP_057450_1410) (HiClip)
Gullies probably formed along the bouldery layers in the upper slopes of this unnamed crater within the last few million years. Gullies eroded these crater slopes and transported sediment downslope forming debris aprons multiple times.
These older apron surfaces were cut by numerous fractures running perpendicular to the slope. Subsequent episodes of gully activity eroded through these fractures and deposited new aprons.
On the floor of the crater are ridges with bouldery layers. These ridges may mark the furthest extent of glaciers that predate much of the original gully activity. Bright flows continue to form in these gullies seasonally.
In the upper gully regions, long shadows cast by jagged outcrops allow scientists to determine the heights and depths of landforms by measuring the length of the shadows cast by the ridges onto the gully floor.
Ross A. Beyer wrote:Impact Near the South Pole (ESP_057152_0985) (HiClip)
This image shows a new impact crater that formed between July and September 2018. It’s notable because it occurred in the seasonal southern ice cap, and has apparently punched through it, creating a two-toned blast pattern.
The impact hit on the ice layer, and the tones of the blast pattern tell us the sequence. When an impactor hits the ground, there is a tremendous amount of force like an explosion. The larger, lighter-colored blast pattern could be the result of scouring by winds from the impact shockwave. The darker-colored inner blast pattern is because the impactor penetrated the thin ice layer, excavated the dark sand underneath, and threw it out in all directions on top of the layer.
Eric Pilles, Matthew Bourassa, Shannon Hibbard and Livio Tornabene wrote:Cross-Section of a Complex Crater (ESP_058057_1465) (HiClip)
This image shows a cross-section of a complex crater in Terra Cimmeria.
Starting in the center, we see a series of peaks with exposed bedrock. These peaks formed during the impact event when material that was originally several kilometers below the surface was uplifted and exposed. The impact also melted the rocks. This eventually cooled, forming the pitted materials that coat the crater floor around the uplift.
The rim of the crater was unstable, and collapsed inwards to form terraces, and we see additional pitted materials between the terraces and the rim. Just outside the crater we can see dark-toned material that was excavated and thrown out after the impact.
Nicole Baugh wrote:A First Look at Dunes (ESP_057903_1390) (HiClip)
This image shows us a cross-section of a dune field. Dune shape depends on several factors, including the amount of sand present and the local wind directions. This dune field displays several distinct dune morphologies.
We see both individual barchan-like dunes and more complex dune shapes. The dunes are arranged in a linear fashion at the northern extent of the field, first in areas with lots of sand, and then with relatively sand-free patches in between dune crests. HiRISE has observed dune activity in other similar fields, but this is our first image over this group of dunes.
A second image is needed to determine if these dunes are also evolving and moving.
Credit: NASA/JPL-Caltech/University of Arizona
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