28 February 2009

The MOC Book: Polar Processes

Posted by Ryan Anderson

I’m falling behind on my blogging of the MOC “book”! We read a lot this week, so I will just stick to the highlights. In other words: mostly pictures, less text. This paper is really all about the pictures anyway! (if you’re just tuning in to the MOC series, check out posts 1,2,3 and 4)

The Martian poles are extremely fascinating but extremely bizarre places. The polar caps are made of water and CO2 ice, and as that ice freezes and thaws, it forms some strange landscapes.

a) South polar "swiss cheese" terrain, formed by sublimating CO2 ice. b) North polar pitted terrain. It is not clear why the north and south pole look so different.

a) South polar "swiss cheese" terrain, formed by sublimating CO2 ice. b) North polar pitted terrain. It is not clear why the north and south pole look so different.

The north and south polar caps are very different-looking, and there is no good explanation for why. This image shows layers from the south and north polar cap. The southern layers are very rough and rugged-looking, while the north polar layers are much smoother.

a) Rough, rugged layers in the south polar cap; b) Very smooth layers in the north polar cap. These layers may reflect changes in the Martian climate driven by changes in the planet's tilt and orbital eccentricity.

a) Rough, rugged layers in the south polar cap; b) Very smooth layers in the north polar cap. These layers may reflect changes in the Martian climate driven by changes in the planet's tilt and orbital eccentricity.

The layers in the north polar cap are amazingly coherent. They can be traced for hundreds of kilometers in some places:

Layers in the north polar cap can be traced for hundreds of kilometers. Prior to MOC, it was thought that the polar cap layers were tens of meters thick, and could be explained solely by changed in the planet's tilt. The fact that these layers are so narrow indicates that there are higher-frequency changes contributing to layer formation.

Layers in the north polar cap can be traced for hundreds of kilometers. Prior to MOC, it was thought that the polar cap layers were tens of meters thick, and could be explained solely by changed in the planet's tilt. The fact that these layers are so narrow indicates that there are higher-frequency changes contributing to layer formation.

Not all of the polar layers are perfectly flat, though. There are some examples of layers that have been deformed, or which intersect with each other, implying that they were subject to tectonics and erosion between periods of deposition.

a) An "angular unconformity", implying that enough time elapsed for some of the layers to become tilted and eroded before the next set were depositied. b) Deformation implies that these layers have a complex history as well.

a) An "angular unconformity", implying that enough time elapsed for some of the layers to become tilted and eroded before the next set were depositied. b) Deformation implies that these layers have a complex history as well.

The paper had a lot of observations, but not many conclusions about the Martian poles. The poles are still not well understood, though missions like Phoenix and MRO are helping to shed some light on the mysterious processes that shape the polar regions.


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