Starship Asterisk*

HiRISE Science Team wrote:

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Naar Crater (ESP_025691_2030)

This impressive crater, that stretches well across the width of the HiRISE camera's footprint, is notable for its sharp rim and steep walls.

There are also some interesting features on the crater floor, not to mention the ejecta blanket, the material surrounding the crater as a result of the original impact. In fact, when viewing this area with other images that have a wider range of view than HiRISE, the ejecta blankets for the craters located here take on the appearance of a flower.

This pattern of ejecta is common with Martian craters. The distinct sharp ends to the flower shaped ejected has led many scientists to suggest that water and ice were engulfed in the ejecta as it was thrown from the crater.

The crater is named after a town in Egypt.

Note: the above image is not map-projected, so North is down.

This is a stereo pair with PSP_007046_2030.

HiRISE Science Team wrote:

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A Youthful Crater and Its Ejecta (ESP_026099_2320)

In this image, we can clearly see the ejecta of this crater, and that tells us the crater appears young and well-preserved. "Ejecta" refers to the material that is excavated from an initial impact and settles back to the surface.

One way we describe a crater as being young is to observe the crater rim. If the rim of a crater doesn't appear that eroded, we often call it "sharp" and "young," even though the impact may have occurred an extremely long time ago.

Given the latitude and proximity to gullies on mesas and massifs in this region, there could also be mid-latitude-type gullies in this crater. At HiRISE resolution, we can get a better look at the ejecta, its distribution and possibly characterize any subsequent modifications we can see in the crater walls.

HiRISE Science Team wrote:

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Sculpting Dunes in Ganges Chasma (ESP_026100_1725)

When dunes are located in a complex topographical area such a canyon, they become ideal candidates for detecting changes to their shapes and sizes over time.

The dunes here in Ganges Chasma--a canyon that's on the eastern end of Valles Marineris--could be strongly influenced by winds, and it's important not to underestimate the erosional power of wind. Because HiRISE has such good resolution, we can track these changes over time to tell us which way a dune is moving, how much, and in what direction. From these observations we can decipher present-day atmospheric processes.

Alfred McEwen wrote:

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Frosted Ground in the Southern Hemisphere in Late Fall (ESP_026388_1280)

This image was acquired within two weeks of the winter solstice, when the subsolar latitude is at its northernmost position.

At this location (latitude 52 S) and time the sun barely peeks over the horizon in the mid-afternoon when MRO passes overhead, and carbon dioxide frost is building up on most of the surface.

In enhanced color, the frost appears blue. Slopes that face north receive more heat from the sun and appear reddish, indicating less frost is present. There may also be a small amount of water frost on the surface.

Mars is very different from Earth in that its main atmospheric component can condense onto the surface. The nitrogen that dominates Earth's atmosphere never condenses onto the surface, although nitrogen in the atmospheres of frigid Triton and Pluto do form surface frost and ice.