Category: Behind The Black

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Cool image time! The picture to the right, cropped and reduced to post here, was taken on March 24, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) as part of a long term monitoring program of the many Martian gullies scientists have found above 30 degrees north latitude on a variety of slopes.

Martian gullies are small, incised networks of narrow channels and their associated downslope sediment deposits, found on the planet of Mars. They are named for their resemblance to terrestrial gullies. First discovered on images from Mars Global Surveyor, they occur on steep slopes, especially on the walls of craters. Usually, each gully has a dendritic alcove at its head, a fan-shaped apron at its base, and a single thread of incised channel linking the two, giving the whole gully an hourglass shape. They are estimated to be relatively young because they have few, if any craters.

…Most gullies occur 30 degrees poleward in each hemisphere, with greater numbers in the southern hemisphere. Some studies have found that gullies occur on slopes that face all directions; others have found that the greater number of gullies are found on poleward facing slopes, especially from 30° to 44° S. Although thousands have been found, they appear to be restricted to only certain areas of the planet. In the northern hemisphere, they have been found in Arcadia Planitia, Tempe Terra, Acidalia Planitia, and Utopia Planitia. In the south, high concentrations are found on the northern edge of Argyre basin, in northern Noachis Terra, and along the walls of the Hellas outflow channels.

Orbital data has identified almost 5,000 gullies on Mars. Based on their shape and the Martian climate, scientists generally think these gullies were formed by some form of water flow, possibly coming from an underground aquifer at their top.
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Today’s cool image illustrates the complex explanations scientists sometimes have to come up with explain the strange geology seen on Mars. The picture to the right, cropped, reduced, and sharpened to post here, was taken on May 30, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows what the scientists label as a whitish “ridged flow-like feature” that appears to exit out of the massive hill to the west.

The white dot on the overview map above as well as in the inset marks this location, smack dab inside the 2,000-mile-long strip of glacier country in the Martian northern mid-latitudes. As you can see from the inset, that massive hill is actual the foot of a large apron of material, likely ice-infused, that has sagged down from the large 5,400-foot high mesa to the west.

The white material is likely what the scientists call an inverted river. Once it was a channel in which either water or ice flowed. With time the weight of that material compacted the riverbed so that it was denser than the surrounding terrain, much of which was likely soft anyway because of a high ice content. When that surrounding terrain eroded away, the riverbed resisted that erosion, and instead became the raised ridge we now see.

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Cool image time! The picture to the right, rotated, cropped, and sharpened to post here, was taken on May 14, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows a small section of a vast dune field, 50 miles square, that sits about 225 miles south of the southern foothills of Mars’ biggest volcano, Olympus Mons.

The dunes are probably less than 20 feet high, with that one small hill only slightly higher. Their similar orientation, which extends across the entire 50-mile-square dune field, indicates the direction of the prevailing winds, which I think (but will not swear to it) is from the southeast to the northwest, which also happens to also follow the grade downhill to the northwest.

It is also possible that wind direction is the reverse, and goes uphill to the southwest.
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