LPSC: Mars: Pingos, Polygons and other Puzzles

I sat in on a large portion of this session about topographical features on Mars, and I have now moved outside to write my thoughts on it at a table by the pool. It’s a little odd to this Canadian to be able to comfortably sit outside in the Sun on only the 10th of March.

These are short, 10-15 minute presentations (15 minute max, including question period) which really require a certain amount of scientific background in the field. I clearly do not have that background, but we’ll see what I learned anyway.

With the help of the internet, I learned that pingos are a periglacial landform (meaning they’re non-glacial, but whose formation is linked to colder climates). They’re essentially mounds of dirt covered ice. On Earth, we find them in the Arctic, subarctic and Antarctica, as tall as 70m with diameters of up to 2km. Apparently, similar such landforms have been observed on Mars by HiRISE. This has important implications for water on Mars.

Unfortunately, given that Pamela and I were late in getting to the conference, I appear to have missed most of the sessions on Martian Pingos. The next set of talks were focusing more on Martian Polygons.

Polygons are again a periglacial feature found on Earth but that we are beginning to see and study in depth on Mars. Patterns of polygons are visible on the ground, with boundaries being troughs or ridges of rocks of different sizes than those inside the polygon.

Martian polygons have been observed with diameter sizes from 3m to 40km (and more), the largest being considered “giant polygons”. Much of the current study of Martian polygons is focussed on those occurring in northern latitudes, particularly the stunning Northern Plaines because the Phoenix mission will be operating in the north.

In the south, the polygons are different because of differences in ice deposits (different amounts at different times as compared to ice deposits in the north). The different ice deposits cause them to have different details. One researcher argues they’re not as stunning as the polygons in the Northern Plaines.

One researcher, Islam, F. did an analysis of the first order mechanics of polygonal fault networks. She presented her findings on giant polygonal fault networks in Utopia Planitia, Mars.

She explained that giant polygons have a typical 1-40km diameter with loosely connected troughs. They have an average fault spacing of 5-6.5km that is controlled by varied topography. The average surface fracture spacing is about 5km, where the minimum is 1km and the maximum she observed in her sample was 17km.

By designing a model that would match her observations of the relation between these aspects and the absolute change in elevation, she concluded that relatively low strain (~0.6-1.2%) and a basement topography (which controls the scale of giant polygons) cause fault networks. Increasing the strain does not cause more faults, it simply increases displacement of materials along the faults.

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