Starship Asterisk*

HiRISE Science Team wrote:

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Martian Honeycomb Hideout (ESP_024061_2610) (video)

The most striking aspect of this image is the honeycomb-like pattern of the dunes.

This is a seasonal monitoring site, meaning HiRISE takes pictures across the seasons to view what changes occur and what causes them. The surface here is covered with seasonal carbon dioxide frost. In this case, we can compare locations of cracks in the frost to previous images.

In this subimage, [to be added], we see a dark spot on the slope of a dune. This is most likely caused by sublimation, where a solid passes directly into a gaseous state. The frost is translucent (some light passes through), so it sublimates at the base and pressure builds up. When the gas escapes, it can expose the dark ground or throw sand on top of the frost, producing dark spots like these.

HiRISE Science Team wrote:

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Defrosting of Dunes with Large Gullies (ESP_024103_2565) (video)

The purpose of this observation is to image dunes where substantial "gullies" formed in the previous Mars winter. These features likely formed due to carbon dioxide defrosting or the weight causing the surface to slump.

The gullies at this site are particularly large, which is intriguing, suggesting that this site be monitored to see if stages of gully formation or details of activity can be observed.

HiRISE Science Team wrote:

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A Sinuous Ridge South of Moreux Crater (ESP_024224_2190) (video)

This observation shows a sinuous ridge that may be an inverted stream. Streams can be inverted (become ridges) if they are made of stronger material than their surroundings.

Another way to make high-standing channels is to have water and sediment flow through a channel in the ice at the bottom of a glacier. After the glacier is gone, the sediment can be left behind, forming a ridge called an esker.

Nathan Bridges wrote:

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Looking for Changes in Colorful Aureum Chaos (ESP_030675_1765) (video)

Although Mars has a thin atmosphere, the wind is nevertheless strong enough to move some sand dunes and ripples (collectively termed "bedforms"). Such changes have been recorded by HiRISE. Our team is continuing to monitor areas with bedforms to see if they have moved.

This image, of Aureum Chaos, is one such region. Aureum Chaos is a jumbled assemblage of large terrain blocks that were disrupted by some ancient process. The edges of the blocks commonly display layered rock strata and the lower regions between the blocks can trap sand. Both are visible here.

In a preliminary comparison with another image acquired two Mars years ago, no bedform changes are obvious, although a more thorough analysis is still needed (the best way to determine if motion has occurred is to get a topographic model of the region and then "warp" the images to fit the topography, thereby removing distortions inherent in the viewing geometry). Nevertheless, this image is rich in geologic detail. If we zoom into one region, abundant, large ripples are visible toward the lower right. On the wall at middle to upper right, two colors of rock are visible, an upper yellowish unit and a lower whitish one. These likely represent distinct rock strata that were deposited before Aureum Chaos formed.