(Sen)- The European Space Agency's Mars Express has gathered evidence that shows two neighbouring craters have completely different geological histories.
The Danielson and Kalosca craters were imaged on 19 June 2011 using a high-resolution stereo camera. The Danielson crater is around 60 kilometres across, whilst the Kalosca crater has a diameter roughly half that of its companion.
The Danielson crater harbours rows of rock protruding from the crater floor, known as yardangs. Sedimentary material first mixed with groundwater, and then cemented into rock, before part of it were eroded away to form the yardangs. Yardangs can reach several hundred metres in length, and are also found in desert regions on Earth.
This erosion was the result of an abrasive wind, which carried grains of dust and sand to batter the bedrock and carve the yardangs. The streamlined appearance and orientation of the yardangs showed that the wind mostly blew in the same direction, which was north-northeast, thus revealing the direction of the prevailing wind at the time. The strong winds were also most likely responsible for depositing the initial sediment needed to create the layered bedrock.
The alternating sedimentary layers in the Danielson crater are mostly of the same thickness and separation. Some scientists think that this might point to cyclic variations in the climate of Mars, which in turn could be caused by changes in the rotation axis of Mars.
The Earth spins on its axis at 23.5 degrees, and this is stabilised by the presence of our Moon. While Mars has a similar obliquity, it has no stabilising moon and so it is thought that the planets axis will swing to various different angles over the years, thus causing changes in the climate.
A 30 kilometre stretch of darker dunes intersects the yardangs, most likely formed during a different era. The darker colour is most likely due to volcanic ash, or volcanic rock that was also the victim of weathering.
The Kalosca crater shows no such evidence of layered sediment. This is most likely because the crater is one kilometre shallower, and thus had no access to the groundwater needed to cement the sediment into rock. It is also possible that the crater is younger, and formed after the water on Mars had dissipated.