Click for full image.
On Mars, one of the most common kinds of landscape is called chaos terrain. Made up of mesas, buttes, and cross-cutting random canyons, this geology is not seen on Earth, and when first identified by scientists in early orbital pictures in the 1970s, it baffled them. While it is clear that some form of erosion process caused it, the scientists did not have enough data then to figure out what that process was.
Today scientists have a rough theory, based on what they now know about Mars’ overall geology and its climate and orbital history. The canyons of chaos terrain were originally fault lines where either water or ice could seep through and widen. See this January 2020 post for a more detailed explanation.
Most of the cool images I have posted of chaos terrain have been in places in the mid-latitudes that are covered with glaciers. See for example this December 2019 post of one particular mesa in glacier country, with numerous glaciers flowing down its slopes on all sides. That mesa is quite typical of all such mesas in the mid-latitudes.
Today’s cool image above, cropped to post here, takes us instead to the Martian very dry equatorial regions. The photo was taken on May 17, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and like mid-latitude chaos, it shows a collection of random mesas with canyons cut almost randomly between.
Unlike the mid-latitudes, however, there is no evidence of glaciers here. Instead, the canyons and mesa slopes are covered with dust, shaped into wind-blown dunes.
As always, the overview map below gives us some context.
The white cross marks the location of today’s image. Located in a chaos region dubbed Iani Chaos, this region is just south of the upstream end of the 1,100-mile-long meandering canyon dubbed Ares Valles. If water or ice once flowed down Ares Valley, it likely came out of Iani Chaos as it carved its canyons and buttes.
In trying to understand the geology in MRO photos, I am finding it increasingly amazing how helpful it is to know the latitude. When something is above 30 degrees latitude you will almost always see some evidence of near surface ice, either from an underground ice table or as buried glaciers.
Below 30 degrees latitude you will instead see no such evidence. Instead, the landscape will — like today’s photo — appear very dry, with the ground either hard bedrock or covered with dust and dunes. (See these two recent posts here and here for similar examples.)
That the nature of the Martian surface is so well determined by latitude is actually one of the more important discoveries scientists have uncovered about Mars in the past two decades. It not only tells them what to expect in each image, it provides some fundamental clues into the entire geological history of the red planet.
That history is not yet completely deciphered, but knowing this one simple fact will make finding the solution much easier.
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