HiRISE Updates (2016 Jan 13)

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HiRISE Updates (2016 Jan 13)

Post by bystander » Thu Jan 14, 2016 10:01 pm

HiRISE Targeting Specialists wrote:

Erosion and Deposition in Schaeberle Crater (ESP_042527_1555) (HiClip)

Schaeberle Crater is a large, heavily-infilled crater with many interesting features. This image shows a window into the crater fill deposit, showcasing eroding bedrock and aeolian landforms.

This pit is located near the geometric center of our image, making it a central pit crater. Central pit craters are thought to form from impact melt draining through subsurface cracks in the deepest part of the crater shortly following impact.

A closeup image shows light-toned bedrock and a small cliff that appears to be weathering away. Below the cliff there are several different types of aeolian features, including ripples and transverse aeolian ridges (TAR). The sand that forms the small, bluish ripples may be weathering out of the cliff face, in contrast to the larger, light-toned TAR which are thought to be currently inactive.

More of the TAR are visible in another closeup image. In this case, they are clearly covered by a dark, ripple-covered sand sheet. We have only imaged this location once, so it is impossible to determine whether or not the sand sheet is blowing in the wind. But due to repeated HiRISE imaging in other areas, active dunes are now known to be common across Mars and we can reasonably speculate that these dunes are moving, too.
Mike Mellon wrote:

Ancient Rivers (ESP_042924_2195) (HiClip)

Early in Martian history, liquid water energetically carved the surface, forming channel systems that look remarkably similar to river valleys and drainage networks on Earth. Exactly how these channels formed—by rainfall, snowmelt, or seepage from underground springs—is often debated.

The answer has important ramifications about the early Martian climate. Clues about the source of the water may indicate the shape, layout, and scale of the various tributaries in a channel system.

Our image shows an example of just such a water-carved channel. The channel pattern, called “dendritic” because of its tree–like branching, begins at the top of the image and runs down over the rim of an ancient impact basin across the basin floor.

The soil surface overlying these channels, and indeed the entire landscape, has been changed and reworked over the intervening millions of years, by the combined actions of wind and ice. Over time, the original channels become muted or even erased. Nevertheless, some characteristics of the smallest tributary channels are still visible at scales seen by HiRISE.
Henrik Hargitai and Ginny Gulick wrote:

Mars 2020 Candidate Landing Site in McLaughlin Crater (ESP_043136_2020) (HiClip)

McLaughlin Crater (21.9 N, 337.6 E) is a large, approximately 95-kilometer diameter impact crater located north of Mawrth Vallis, in Arabia Terra, a region that was made famous by the book and movie “The Martian” by Andy Weir.

McLaughlin Crater straddles three major terrain types: the Northern lowlands, the Southern highlands and the Mawrth Vallis region. The crater floor is thought to be covered by clays and carbonates that were deposited in a deep lake at least 3.8 billion years ago perhaps by ground water upwelling from beneath the crater floor (Michalski et al, 2013, Nature Geoscience).

McLaughlin Crater is listed as a candidate landing site for the 2020 Mars surface mission. Although it is described as a “flat, low-risk and low-elevation landing zone,” the region in this image on the southern floor of the crater shows a complex surface of eroded layers that are rough in places. An unusual feature is a straight fracture cutting diagonally across the layered material at the bottom portion of the image that may be a fault line.

This is a stereo pair with ESP_042991_2020.
Kirby Runyon wrote:

A Young, Fresh Crater in Hellespontus (ESP_043398_1600) (HiClip)

This is a textbook example of a morphologically fresh and simple impact crater. At 1.3 kilometers in diameter, this unnamed crater is only slightly larger than Arizona’s Barringer (aka Meteor) Crater, by about 200 meters. Note the simple bowl shape and the raised crater rim.

Rock and soil excavated out of the crater by the impacting meteor—called ejecta—forms the ejecta deposit. It is continuous for about one crater radius away from the rim and is likely composed of about 90 percent ejecta and 10 percent in-place material that was re-worked by both the impact and the subsequently sliding ejecta.

The discontinuous ejecta deposit extends from about one crater radius outward. Here, high velocity ejecta that was launched from close to the impact point—and got the biggest kick—flew a long way, landed, rolled, slid, and scoured the ground, forming long tendrils of ejecta and v-shaped ridges.

Credit: NASA/JPL-Caltech/University of Arizona

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