Antarctica

This week’s guess the planet image comes from Earth and shows a region of Antarctica near the ross ice sheet. This image comes from Google Earth, and if we look at a larger view of the same area we can see that the glaciers flow down onto an ice shelf, which is breaking up into icebergs as it meets the sea. The area is striking as we can see several large valleys separated by rocky mountains. These valleys are covered by glaciers, and you can see lines in the ice which indicate how it is flowing down between the mountains. Several glaciers merge at the confluence of these valleys and you can see the ridges where the streams of ice meet. 

There is another region, not far from this part of Antarctica, which doesn’t look as striking in aerial photographs, but which I want to talk about as it is very significant for planetary science. This area is characterised by a very different property to the wet and icy regions seen above. This is the Antarctic dry valleys, the location of which are shown in the map below. These valleys are of great interest to both Earth scientists and those who study other planets. This is because; despite lying in ice locked Antarctica they are one of the driest places on Earth. The cold conditions in this part of Antarctica mean that there is very little precipitation, creating a cold desert which is an excellent reference point for studying the cold, dry environments of planets like Mars. 

 

Unlike most of Antarctica the dry valleys are mostly free of ice, and form a gravelly desert interspersed with polygonal patterned ground. This landscape looks a lot like some of the polar regions of Mars and is thus a prime candidate for analogue science. I’ve talked a lot about how similar features recur from one planet to another. By understanding how something evolves under terrestrial conditions we can extrapolate its behaviour on another world. In order to do this effectively we first need to find good counterparts for comparison. A lot of planetary science consists of comparing the landscapes of other planets to known terrestrial features to see which familiar landforms are the best fits. Sometimes we can do this in reverse. 

In addition to studying the landscape of the dry valleys we can look at their ecosystems as well. This is one of the most hostile places on Earth, and so very little life survives here. The hardy species which have evolved to occupy the dry valleys have very similar adaptations to those which would be needed to survive on the cold, dry and salty surface of Mars. Astrobiologists can study samples of these organisms, which are called “extremophiles” because they like very extreme environments. Organisms are collected from very cold or dry environments, and cultured in the lab. They can then be exposed to exaggerated conditions, which more accurately simulate the environment of other planets. This allows us to see whether they can evolve further to occupy a far more frigid niche, or whether there are limits beyond which they become dormant or die off. 

Almost every environment on Earth is inhabited by some sort of organism, however they have an advantage over those which might be found on other worlds. Terrestrial extremophiles can evolve from life forms that originated in less hostile environments, but which became progressively hardier as they moved into more dangerous climates. Many of these organisms could now survive under martian conditions, at least to an extent, however it is less certain that they could have evolved there from scratch. We thus need to consider whether Mars harbours small areas which are warmer or wetter. These would be more suitable for life to emerge and evolve, before expanding to colonise the more hostile areas. This sends us back to our spacecraft data to look at the landscape once more, and speculate as to which features of the environment might by indicative of warmer climates. 

 

For example we do see glacier like forms on Mars. This image from HiRISE looks strikingly similar to the image of terrestrial glaciers above. We see the same flow of material through a constricted valley and very similar lines and bands. This doesn’t necessarily mean that it is a wetter environment, there may not be any ice left in this martian glacier, as it could all have sublimated long ago, leaving only the dust and debris which it deposited. Nonetheless features like this are a clear indicator of the presence of large quantities of ice at some point during their geological history, and hint at a dynamic environment in the past if not the present.  Check out the page for this HiRISE image which has some more information about debris covered glaciers on Mars.

Image credits:

Antarctic glaciers via Google Earth

Map of the Antarctic dry valleys, USGS public domain image, via Wikipedia

HiRISE image of martian glacier like form via Wikipedia.