Weird mottled terrain in the dry tropics of Mars
Cool image time! The picture to the right, cropped, reduced, and enhanced to post here, was taken on October 28, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled by the science team as “mottled ridged terrain,” it shows a relatively flat area of scattered broken-up flat-topped ridges and knobs, following no clear pattern of formation.
In trying to research this, I could only find one paper [pdf] discussing this kind of mottled ridges that did a survey of similar features across a large region to the northwest. That paper could not determine what caused such features, but came up with hypothesis. From the abstract:
While it is not possible to determine the precise formation mechanism of these polygonal ridge networks from our new data, their formation can be assessed in terms of three possibly separate processes: (1) polygonal fracture formation, (2) fracture filling and (3) exhumation. We find that polygonal
fracture formation by impact cratering and/or desiccation of sedimentary host deposits is consistent with our results and previous spectral studies. Once the polygonal fractures have formed, fracture filling by clastic dikes and/or mineral precipitation from aqueous circulation is most consistent with our results. Exhumation, probably by aeolian processes that eroded much of these ancient Noachian terrains where the ridges are present caused the filled fractures to lie in relief as ridges today.
To put this in plain terms, the initial polygon-patterned cracks were formed by either an impact or the drying out of the surface (similar to the cracks seen on dried mud here on Earth). Both could have contributed. Then material welled up from below, either lava or mud, that hardened to fill the cracks. Later erosion by wind stripped away the surface, leaving behind these broken ridges.
As always, the location adds some very interesting context.
» Read more
Cool image time! The picture to the right, cropped, reduced, and enhanced to post here, was taken on October 28, 2025 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). Labeled by the science team as “mottled ridged terrain,” it shows a relatively flat area of scattered broken-up flat-topped ridges and knobs, following no clear pattern of formation.
In trying to research this, I could only find one paper [pdf] discussing this kind of mottled ridges that did a survey of similar features across a large region to the northwest. That paper could not determine what caused such features, but came up with hypothesis. From the abstract:
While it is not possible to determine the precise formation mechanism of these polygonal ridge networks from our new data, their formation can be assessed in terms of three possibly separate processes: (1) polygonal fracture formation, (2) fracture filling and (3) exhumation. We find that polygonal
fracture formation by impact cratering and/or desiccation of sedimentary host deposits is consistent with our results and previous spectral studies. Once the polygonal fractures have formed, fracture filling by clastic dikes and/or mineral precipitation from aqueous circulation is most consistent with our results. Exhumation, probably by aeolian processes that eroded much of these ancient Noachian terrains where the ridges are present caused the filled fractures to lie in relief as ridges today.
To put this in plain terms, the initial polygon-patterned cracks were formed by either an impact or the drying out of the surface (similar to the cracks seen on dried mud here on Earth). Both could have contributed. Then material welled up from below, either lava or mud, that hardened to fill the cracks. Later erosion by wind stripped away the surface, leaving behind these broken ridges.
As always, the location adds some very interesting context.
» Read more












