HiRISE Science Team wrote:Breccia with Large Clasts (ESP_025600_1735)
In this beautiful image there appears to be a breccia layer, or a layer composed of rock fragments embedded in a finer material. This particular breccia is made up of fragments (or "clasts" as they are known to geologists) so large they can be seen by HiRISE.
The breccia layer, seen most easily near the center of this image, seems to be more resistant to erosion than the surrounding material, serving as a caprock to protect the layers beneath it.
The HiRISE team is planning on acquiring another image over this area in order to create a stereo (3-D) pair. This will help scientists better understand the topography and stratigraphy of the area.
This is a stereo pair with ESP_026523_1735.
Mike Mellon wrote:In the Transition Zone (ESP_025675_2255)
Nestled between mesas, this image shows the valley floor where eroded rocky and/or soil debris appears to have flowed viscously from the msea walls across the valley to merge. A leading theory is that ice and snow became entrained with the soil debris as it shed from the mesa. This combined ice-rich debris then flowed slowly downhill. "Rock glaciers" on Earth are an analogous landform that flow viscously like a glacier, lubricated by ice trapped in the pore spaces.
The image shows light toned viscous debris that overlays a darker toned surface. Both surfaces sport irregular fracture patterns and evidence that substantial erosion has since taken place. The upper viscous-flow surface also contains abundance small, regular polygonal patterns. Such patterns are commonplace in permafrost on Earth, and are typically considered strong evidence for shallow subsurface ice.
Erosion and the formation of small scarps reveal a multitude of layers within the subsurface. Such structure is unusual for a single glacial flow and may indicate episodic glacial advance and retreat. Additionally, the sparse population of rocks on the surface and along the eroded scarps suggest that the debris eroding from the mesas consists largely of soil.
Cathy Weitz wrote:A Trough within Ladon Basin (ESP_026416_1620)
This image shows an approximately 2-kilometer wide trough within Ladon Basin. This trough, and others around the perimeter of the basin, were probably produced during the gradual sinking of the materials here.
The basin formed during an epoch in Martian history called the Noachian period, and may have harbored a lake based upon the fluvial valleys that flow into it. If a lake once existed here then the trough is a window that could expose any sediments deposited within the lake, making this an exciting image to explore.
Alfred McEwen wrote:Expanded Craters on Icy Terrain (ESP_026510_2310)
The middle of this image contains a cluster of depressions (craters) with two levels: a small inner crater, surrounded by a shallow depression extending outward from the inner crater.
This image is located at 50 degrees north latitude, where shallow ice has been mapped by the Mars Odyssey spacecraft. MRO has detected newly-formed impact craters in this broad region that exposed shallow ice, and also revealed that it is nearly pure ice.
One interpretation of the expanded craters visible here is that a group of small impacts, probably secondary craters from a much larger primary crater, exposed the clean, shallow ice in this region. Once exposed, the ice is unstable and sublimates (passes directly from ice to gas), and the shallow depressions could gradually expand.
Credit: NASA/JPL/University of Arizona
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