You have asked!
Hi! I am a martian scientist and the member of Planet Four team. I am trying hard to answer many questions that you post in our forum. I notice that some questions come up more often than others, indicating what we have missed in our FAQs page.
I will try to post here about the topics that appear multiple times in the forum. And as first example, I want to tell you about one image that actually taught me something new. This one:
Many people asked, what are these parallel lines and how can so straight lines be of natural origin. First I thought that these are glacier marks. Until I realized that they are not depressions, but ridges. To clear up what they are I asked my colleague Mikhail Kreslavsky from University of California in Santa Cruz. He has much more experience in martian polar geology and glaciology than I do. This was his answer:
These are yardangs, traces of aeolian (that is wind-related) erosion. They are long parallel ridges. They form when wind removes soft, friable material and are oriented along the direction of the strongest winds. Yardangs are known in deserts on the Earth and are abundant on Mars. In this particular place, yardangs are remarkably regular, long, parallel. This fascinating regularity is probably caused by coincidence of two things. First, the material here is very homogeneous; it is slightly cemented dust; there are no embedded boulders, etc. This is the material of the South polar layered deposits, it was deposited from the atmosphere as a mixture of snow, frost and dust under different climate conditions in the past. Recently (geologically recently, hundreds of thousands of years) ice (former snow and frost) sublimated (evaporated) from the near-surface layer of this material, and the remaining slightly cemented dust is friable and homogeneous. Second, the strongest winds in this place are very stable. The polar layered deposits have a general shape of a ~700 km wide ~3 km high dome. The strongest winds here are so-called katabatic winds made by flow of cold (=dense) air from the pole on top of the dome downhill. People who have been to Antarctica or Greenland know katabatic winds very well. Because katabatic winds are controlled by slopes, they are much more stable than winds controlled by weather phenomena. The direction of the spring-time fans in this region often differs from the direction of the yardangs, because spring-time winds are not those strongest winds that shape the surface.
I hope, similar to me, you also enjoyed getting to know something new about Martian geology today.
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