HiRISE Updates (2015 May 20)

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HiRISE Updates (2015 May 20)

Post by bystander » Sat May 23, 2015 3:07 pm

Alfred McEwen wrote:

Seasonal Flows in Asimov Crater (ESP_040485_1330) (HiClip)

Seasonal flows called recurring slope lineae (RSL) grow down warm slopes in the summer, fade when they become inactive, then re-form the following year when the slopes warm up again from the Sun.

We see many of these RSL over the steep equator-facing slopes of the troughs within Asimov Crater, as illustrated in this cutout. However, just a few days later HiRISE imaged another steep equator-facing slope in Asimov crater, and no RSL are visible at all (ESP_040551_1330). These two slopes are very similar in slope angle, rockiness, and other properties seen by HiRISE.

Why are RSL present in one place but not another that appears so similar? RSL activity must be controlled by something that HiRISE can't detect, such as the presence of salts or groundwater. It is also possible that in future years, the RSL activity will appear or disappear on each slope.
Alfred McEwen wrote:

Honey, I Shrunk the Mesas (ESP_040566_0935) (HiClip)

The South Polar residual cap (the part that lasts through the summer) is composed of carbon dioxide ice. Although the cap survives each warm summer season, it is constantly changing its shape due to sublimation of carbon dioxide from steep slopes and deposition onto flat areas.

This observation was acquired on 23 March 2015, in the summer of Mars Year 32. The same area was imaged in another observation on 28 August 2007, (PSP_005095_0935) in the summer of Mars Year 28. You can barely recognize that this is the same area! The high-standing mesas have shrunk to about half of their size in 2007, but the low areas between mesas have filled in with new carbon dioxide material.
Alfred McEwen wrote:

Sedimentary Rock Layers on a Crater Floor (ESP_040605_1575) (HiClip)

This image covers layered sedimentary rocks on the floor of an impact crater north of Eberswalde Crater. There may have been a lake in this crater billions of years ago, and the area was once considered a landing spot for the Mars Science Laboratory.

There are diverse rock compositions, as we can see in an enhanced-color cutout. This image completes a stereo pair, so be sure to view the stereo anaglyph. Here is a sample at full resolution.

This is a stereo pair with ESP_032706_1575.
Alfred McEwen wrote:

Alluvial Fans in Mojave Crater (ESP_040618_1875) (HiClip)

Stereo data from an anaglyph (or 3D) image shows that the landscape in this observation is pervasively eroded, right up to the tops of the ridges, with channels extending down into depositional fans much like alluvial fans in the Mojave Desert.

This can be explained by something like rainfall, but this crater is geologically young, only a few hundred million years old, when Mars’ atmosphere was thought to be too depleted to support rainfall. From the surrounding region we can see that only the Mojave ejecta is eroded, not adjacent landscapes. This suggests that the ejecta landed wet and itself initiated the erosion, rather than rainfall from clouds.

Subsurface ice may have melted and mixed with the crater ejecta, which fell as a wet slurry of debris. But that's just my favorite theory—other geologists favor different interpretations.

This is a stereo pair with ESP_039695_1875.

Credit: NASA/JPL/University of Arizona

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