Where the Martian landscape begins to dry out
Click for original image.
Today’s cool image to the right, cropped, reduced, and sharpened to post here, provides us a glimpse at the lower mid-latitudes of Mars where the terrain is beginning to dry out as we move south. The picture was taken on April 29, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what the scientists label “large linear features.”
The main north-south ridge is only about 20-25 feet high, and its meandering nature (which can be seen more clearly in the full image) suggests it is possibly an inverted channel, formed when the bed of a former canyon gets compressed by the water or ice that flows through it, and when the surrounding terrain gets eroded away that channel bed becomes a ridge.
These ridges however could also possibly be volcanic dikes, where magma had pushed up through fractures and faults to form these more resistant ridges.
On the overview map to the right the red dot in the inset marks the location, on the southern cratered highlands just south of the chaos terrain dubbed Nilosyrtis Mensae. Nilosyrtis forms the eastern end of the 2,000-mile-long northern mid-latitude strip I dub glacier country, because almost every image shows a surface covered with glacial features.
Today’s picture is located at 32 degrees north latitude, at the point where glacial features begin to disappear on Mars. As one travels south from here the ground becomes exposed, as it is this image, dry bedrock with no evidence of near surface ice. By the time you reach Perseverance in Jezero Crater at about 18 degrees north latitude you are in a dry, barren, but very cold desert.
The intriguing aspect of the ridges in this image is that they appear to be an example of chaos terrain, in reverse. The chaos terrain in glacier country is made up of mesas criss-crossed by straight canyons. Here, we have straight ridges criss-crossing lower terrain. The origin of both geologies are probably related, as the ridges and canyons likely mark the locations of fault lines. The mystery is why the difference. In the northern icy mensae region the material in those fault lines erodes away first. Here however it is more resistant.
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