Starship Asterisk*

by **bystander** » Sat Jan 28, 2017 4:11 pm

Candy Hansen wrote:
How Gas Carves Channels (ESP_046845_0975) (HiClip)

A layer of dry ice covers the South Polar layered deposits every winter. In the spring, gas created from heating of the dry ice escapes through ruptures in the overlying seasonal ice, entraining material from the ground below. The gas erodes channels in the surface, shown in this image, generally exploiting weaker material.

The ground likely started as polygonal patterned ground (common in water-ice-rich surfaces), and then escaping gas widened the channels. Fans of dark material are bits of the surface carried onto the top of the seasonal ice layer and deposited in a direction determined by local winds.

This target was suggested by the citizen scientists at Planetfour : Terrains.

Elise Harrington, Arya Bina, Eric Pilles, and Livio Tornabene wrote:
Contact between Two Distinct Types of Bedrock Northwest of Hellas Planitia (ESP_047762_1585) (HiClip)

In this context image is an old degraded crater that has undergone a complex history of burial and erosion. The image shows a surface with at least two types of exposed bedrock, one that is light-toned and one that is dark. An enhanced color infrared image highlights these two exposures in yellows and blues, which such colors representing altered and unaltered surfaces, respectively.

The overlying, rougher blueish-toned bedrock appears to have undergone the most extensive erosion, revealing the smoother, fractured yellowish-toned bedrock below. We see windblown (aeolian) bedforms across the image, possibly the culprit behind the erosive forces that have removed and uncovered the underlying yellowish-toned bedrock visible today.

Ginny Gulick wrote:
Pits and Channels of Hebrus Valles (ESP_048036_2025) (HiClip)

The drainages in this image are part of Hebrus Valles, an outflow channel system likely formed by catastrophic floods.

Hebrus Valles is located in the plains of the Northern lowlands, just west of the Elysium volcanic region. Individual channels range from several hundred meters to several kilometers wide and form multi-threaded (anastamosing) patterns. Separating the channels are streamlined forms, whose tails point downstream and indicate that channel flow is to the north. The channels seemingly terminate in an elongated pit that is approximately 1875 meters long and 1125 meters wide. Using the shadow that the wall has cast on the floor of the pit, we can estimate that the pit is nearly 500 meters deep.

The pit, which formed after the channels, exposes a bouldery layer below the dusty surface mantle and is underlain by sediments. Boulders several meters in diameter litter the slopes down into the pit. Pits such as these are of interest as possible candidate landing sites for human exploration because they might retain subsurface water ice (Schulze-Makuch et al. 2016, 6th Mars Polar Conf.) that could be utilized by future long-term human settlements.

Candy Hansen wrote:
Rectangles with Wiggly Sides (ESP_048124_0975) (HiClip)

Ground that has a lot of water ice mixed with dirt tends to crack in polygonal patterns bounded by short straight channels. In the South Polar region of Mars this type of terrain may be covered by a seasonal polar cap composed of dry ice.

In the spring as the seasonal cap sublimates gas is trapped underneath the seasonal ice layer until it can escape to an opening. At this site, faint rectangular channels in the surface are visible. The escaping carbon dioxide gas has exploited these channels and in the process, deepened them and added sinuosity to the formerly straight segments.

This interesting site was identified by citizen scientists at Planetfour: Terrains.

Credit: NASA/JPL-Caltech/University of Arizona

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