Dune field

This week’s guess the planet picture comes from much closer to home than some of our previous images. This is a scene of the Taklamakan Desert on Earth. This sandy region in western china is quite sparsely inhabited. It is the world’s second largest “erg” or area of continuous sand. Many other deserts are larger, but only the interior of the Arabian peninsula has a larger expanse of shifting sand.  

Since this image comes from Earth we can get some good colour pictures for a change. Here is an alternate view, of an area a little to the west of the section I posted on Monday.

 Here you can see a road crossing the desert on the left hand side of the image. Credit for this picture goes to the Landsat team, and Google Earth. The striking dune patterns we see here are the result of aeolian processes, which means that they are shaped by the wind. This means that dune fields can only occur on planets which have a significant atmosphere. Most of the larger terrestrial planets have an atmosphere of some sort. Earth and Venus have the thickest atmospheres, while that of Mars is much thinner. Mercury and many of the solar system’s moons are largely airless, they do not have sufficient gravity to retain an atmosphere so gases which form there are quickly lost to space. 

Whether a planet has an atmosphere or not has huge implications for the geomorphology, because the movement of air is a very important process for eroding and weathering a planet’s surface. 

Erosion is the process which breaks down the surface of the planet, shattering stone and grinding down mountain ranges. It can occur through a variety of different processes including wind, water, chemistry and life. On bodies which lack most of the above the most significant erosive force can be the impact of meteorites. Chemical weathering can theoretically occur anywhere, but generally requires water to get the process started.

Dune fields and ergs are found across the solar system. Mars has small dune fields in many of its impact craters. Massive ergs surround the polar caps. Dune fields have been observed on Venus and on Titan. 

Studying the dune patterns can tell you a lot about the prevailing winds and the material which is being moved around by them. I’ll be featuring a few different types of dunes in future posts. The ones we’re looking at today are called linear dunes. They consist of parallel ridges of sand, generally waving. The direction of sand movement is along the long axis of the dunes. These often form in bidirectional wind regimes, where there are two dominant wind directions. This is very useful information if we are looking at another planet, and can’t put sensors ont he ground to measure wind speeds.