Kirby Runyon wrote:Monitoring Sand Sheets and Dunes (ESP_050182_1165)
This crater features sand dunes and sand sheets on its floor. What are sand sheets? Snow fall on Earth is a good example of sand sheets: when it snows, the ground gets blanketed with up to a few meters of snow. The snow mantles the ground and “mimics” the underlying topography. Sand sheets likewise mantle the ground as a relatively thin deposit.
This kind of environment has been monitored by HiRISE since 2007 to look for movement in the ripples covering the dunes and sheets. This is how scientists who study wind-blown sand can track the amount of sand moving through the area and possibly where the sand came from. Using the present environment is crucial to understanding the past: sand dunes, sheets, and ripples sometimes become preserved as sandstone and contain clues as to how they were deposited.
This is a stereo pair with ESP_050261_1165.
Kirby Runyon wrote:A Crater on a Crater Wall (ESP_050259_1380)
It’s not that common to see craters on steep hills, partly because rocks falling downhill can quickly erase such craters. Here, however, a small impact occurred on the sloping wall of a larger crater and is well-preserved.
Dark, blocky ejecta from the smaller crater has flowed downhill (to the west) toward the floor of the larger crater. Understanding the emplacement of such ejecta on steep hills is an area of ongoing research.
Arya Bina and Livio L. Tornabene wrote:Decoding a Geological Message (ESP_049167_1855)
A close up image of a recent 150-meter diameter impact crater near Amazonis Mensa and Medusae Fossae is another great example of geologic complexity of Mars. The spider web-like texture of this crater is intriguing. But what does it mean?
On Earth, we have many geologic mechanisms that embrace the surface of the planet in an almost constant state of metamorphosis. Although Mars is not nearly as geologically active as Earth, it is still a host to many processes that shape its surface even today (e.g., aeolian modification, periglacial processes, recent impacts, etc.). The appearance of the ejecta of this crater is likely a combination of both the characteristics of the target material it was deposited on, and processes that modified and degraded it over time.
When we look to other images in this region we find a similar texture. This texture is referred to as “yardangs” by scientists who study wind erosion. Yardangs are streamlined ridge-and-trough patterns formed by the erosion of wind dominating from a specific direction; in this particular case, from the southeast to the northwest. The specific direction of the winds is supported by regional context images that show many craters in the region have wind streak “tails” that points to the northwest.
Craters of this size have been observed to form recently on Mars, so the fact that this crater is modified speaks volumes, and gives us a chance to decode some geological messages from Mars.
Jon Kissi, Livio L. Tornabene, Zach Morse, Eric Pilles, and Gavin Tolometti wrote:The White Cliffs of “Rover” (ESP_050282_1820)
This image reminds us of the rugged and open terrain of a stark shore-line, perhaps of an island nation, such as the British Isles. A close-up in enhanced color produces a striking effect, giving the impression of a cloud-covered cliff edge with foamy waves crashing against it.
The reality is that the surface of Mars is much dryer than our imaginations might want to suggest. This is only a tiny part of a much larger structure; an inverted crater—a crater that has been infilled by material that is more resistant to erosion than the rocks around it—surrounded by bluish basaltic dunes. The edge of these elevated light-toned deposits are degraded, irregular and cliff-forming.
Dunes visible below the cliff, give the impression of an ocean surface, complete with foam capped waves crashing against the “shore line,” demonstrating the abstract similarity between the nature of a turbulent ocean and a Martian dune field.
Meridiani Planum has an overall smooth terrain, which starkly contrasts with the more common boulder- and crater-laden landscapes observed over much of the rest of Mars. This makes it relatively younger in character than many other areas of the planet. Meridiani is one of the Mars Exploration Rover landing sites, and, is known for its layers and sediments. The orbital detection of hematite was one of the main reasons for sending Opportunity to this area.
Salt-bearing rocks—also called sulphates—were observed in the very first image from Opportunity, so perhaps it’s apt that this HiRISE image reminds us of the turmoil and rugged beauty of a cliff-face, a coastline, being worn down by a relentless sea.
Credit: NASA/JPL-Caltech/University of Arizona
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