Livio Leonardo Tornabene wrote:Better Preserved on Mars than on Earth (ESP_014096_1975)
In many ways, Mars bears remarkable similarities to Earth, but in some ways it is drastically different. Scientists often use Earth as an example, or analog, to help us to understand the geologic history of the Red Planet.
As we continue to study Mars, it is vitally important to remember in what ways it differs from Earth. One very apparent way, readily observed from orbit, has to do with its preservation of numerous craters of all sizes, which are densest in its Southern hemisphere. Earth has comparatively little preserved craters—about 1,000 to 1,500 times fewer—due to very active geologic processes, especially involving water. When it comes to impact craters, there are some things that can no longer be observed on Earth, but can be observed on Mars.
This color composite shows one such example. It covers a portion of the northern central peak of a unnamed, 20-kilometer crater that contains abundant fragmental bedrock called “breccia.” The geological relationships here suggest that these breccias include ones formed by the host crater, and others formed from numerous impacts in the distant past.
Because there are fewer craters preserved on Earth, terrestrial central uplifts do not expose bedrock formed by previous craters. It may have been the case in the past, but such craters were destroyed over geologic time.
This is a stereo pair with ESP_020043_1975.
Alfred McEwen wrote:Old Features and New (ESP_021699_1405)
This image covers a portion of a typical impact crater in Terra Sirenum at about 40 degrees south latitude on Mars.
At the top of the image, outside the crater rim, there is a mid-latitude mantle, rough in places where ice may have sublimated. Below the crater rim, on the steep, south-facing slope, are gullies. These are erosional features with depositional fans. Some of the gully fans have a bluish color: these are probably quite recent deposits, less than a few tens of years old.
On the floor of the crater (bottom of this image) are ridges that likely formed from the flow of ice, perhaps a few million years ago.
Alfred McEwen wrote:A Dust Devil on Hilly Terrain (PSP_009819_2130)
There are many dust devils on Mars—little twisters that raise dust from the surface. They have also cleaned dust off of the solar panels of the rovers Opportunity and Spirit, improving the solar power production. (Spirit became stuck in 2009 and ceased communication a year later.)
HiRISE sees many dust-devil tracks on Mars, but rarely captures an active feature because the images cover such small areas and because the typical time of day near 3 p.m. is past the peak heating and dust-devil activity. In this 2008 image in the Amazonis region, we got lucky, although not lucky enough to capture the whole swirl in the color strip.
Serina Diniega wrote:Scars of Erosion (ESP_020876_1330)
This large crescent dune in Kaiser Crater shows the scars of many types of seasonal erosional activities. Along its downwind slope are large gullies which are active during winter, when frost drives dune material downslope, carving out channels and creating fan-shaped aprons.
On the upwind slope (bottom), dust devil tracks are visible: dark lines and curliques created during the spring season by small wind vortices vacuuming up a thin layer of dust and exposing the dark dune sand.
Note: Both the cutout and the above image are rotated so that North is to the right.
This is a stereo pair with ESP_021720_1330.
Credit: NASA/JPL-Caltech/University of Arizona
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