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Numerous layers in the interior slopes of Argyre Basin on Mars

Numerous layers on Mars
Click for original image.

The cool image to the right, cropped, reduced, and enhanced to post here, was taken on February 22, 2024 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It gives us another example the many-layered geological history of Mars, seen in numerous locations across the entire Martian surface.

This example shows many thin layers, going downhill about 450 feet from the mesa near the bottom of the picture to the low point near the picture’s top. At this resolution there appear to be roughly two dozen prominent layers in that descent, but a closer look suggests many more layers within those large layers. Like the terrain that Curiosity is traversing on Mount Sharp, the closer one gets the more layers one sees. And each layer signifies a different geological event, possibly even marking the annual seasons, each either adding or removing a layer of dust or ice, or placing down a new layer of lava.

Overview map

The overview map to the right provides the larger context. These layers are on the southern interior slopes of Argyre Basin, as indicated by the white dot. The first inset on the left shows us that within these slopes is this very large gully that suggests something once leeched out of those slopes. To its west close-by is this 5-mile-wide unnamed crater, shown in better detail in the second inset on the right. The rectangle in that second inset shows the area covered by the picture above.

The orbital imagery suggests this crater is not from an impact, but is a sinkhole caused by some form of erosion. The crater has no upraised rim, as would be seen from an impact. It is also not round, but distorted in shape. Moreover, the gaps on the east and west rims suggest past drainage downhill to this crater from both directions, slowly wearing away the surface to expose those layers. The low point in the picture is actually the saddle of the western gap. The layers can be seen all along the entire interior rim, once again suggesting that the depression is a sinkhole, not an impact crater, since that interior rim appears to have formed slowly over time, not instantly by an impact.

As the latitude is about 54 degrees south, it is very likely there is a lot near surface ice. Since this is the north-facing slope of Argyre, it gets the most sunlight year round. That sunlight could be causing that near-surface ice to sublimate into gas, which then leaks out to form that large gully as well as this depression.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.

The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.

"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News

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