Alfred McEwen wrote:A South Polar Pit or an Impact Crater? (ESP_049972_0930)
It is late summer in the Southern hemisphere, so the Sun is low in the sky and subtle topography is accentuated in orbital images.
We see many shallow pits in the bright residual cap of carbon dioxide ice (also called “Swiss cheese terrain”). There is also a deeper, circular formation that penetrates through the ice and dust. This might be an impact crater or it could be a collapse pit.
This is a stereo pair with ESP_049945_0930.
Alfred McEwen wrote:Active Flows on Steep Slopes in Ganges Chasma (ESP_049981_1710)
This image covers a steep west-facing slope in southwestern Ganges Chasma, north of the larger canyons of Valles Marineris. The spot was targeted both for the bedrock exposures and to look for active slope processes.
We see two distinct flow deposits: lobate flows that are relatively bright, sometimes with dark fringes, and very thin brownish lines that resemble recurring slope lineae (or “RSL”). Both flows emanate from rocky alcoves. The RSL are superimposed on the lobate deposits (perhaps rocky debris flows), so they are younger and more active.
The possible role of water in forming the debris flows and RSL are the subjects of continuing debate among scientists. We will acquire more images here to see if the candidate RSL are active.
Alfred McEwen wrote:A Triple Crater (ESP_049987_1450)
This image (making a stereo pair with ESP_041350_1455) shows an elongated depression from three merged craters.
The raised rims and ejecta indicate that these are impact craters rather than collapse or volcanic landforms. The pattern made by the ejecta and the craters suggest this was a highly oblique (low angle to the surface) impact, probably coming from the west.
There may have been three major pieces flying in close formation to make this triple crater. Be sure to view the anaglyph for a more detailed look.
This is a stereo pair with ESP_041350_1455.
Nicole Bardabelias wrote:Gullies and Craters and Dunes, Oh My! (ESP_050111_1305)
This unnamed, approximately 30-kilometer diameter crater, formed in the Southern highlands of Mars. Our image shows regions of geologic diversity within, making this an interesting spot for scientists to study how different Martian processes interact with each other.
Gullies, or channels formed by fluids such as water or lava, cut into the rim and sides of this crater. The presence of gullies can reveal clues about the ancient history of Mars, such as the amount of flowing fluid needed to form them and roughly how long ago that happened. This crater may also host features actively changing on the surface of Mars known as “recurring slope lineae” (RSL). Manifesting as dark streaks on steep slopes such as the walls of craters, scientists posit briny flows of small volumes of water as a possible RSL formation method. Studying the behavior of RSL further may provide evidence for the presence of water on Mars today.
Moving toward the crater floor, one can observe patterns indicative of dunes. Dunes arise from the breakdown of exposed rocks by wind and subsequent manipulation of the eroded sand particles into wave-like structures. The presence of dust devil tracks provides additional evidence for significant wind activity at this location. These dunes are very dusty and so likely haven't been active (moved) in some time.
HiRISE also captured a small, relatively fresh crater on the floor near the dunes. One of the most ubiquitous processes in the solar system, impact cratering can drastically change the surface of a planetary body. As such, craters provide sources of comparison between planets, moons, and other bodies across the solar system. Impacts still occur today, helping scientists find relative ages of different areas of a planet and discover materials buried under the surface.
All of these processes have altered the surface of Mars in the past and continue to do so today. Since gully formation, wind erosion, and impact cratering could have interacted with each other for many years, planetary scientists find it difficult to work backwards and make definitive statements about ancient Martian history. However, HiRISE imagery has aided in closing these gaps in our scientific knowledge.
Credit: NASA/JPL-Caltech/University of Arizona
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