ESA’s Mars Express probe has been exploring Mars from orbit for more than twenty years. The way it mapped the surface with its High Resolution Stereo Camera (HRSC) has drastically changed the way we see the Red Planet. In a recent paper, ESA released a series of HRSC images highlighting the heavily cratered Arabia Terra region. The study of Martian craters provides insights into Mars’ geology, meteorology, and its long and turbulent history. The images were generated from the camera’s digital terrain model as well as the nadir and color channels.
The image above shows the Arabia Terra region, a large plain in the southern highlands that is heavily cratered by impactors that have struck the planet over time. The features are labeled (if you click on the image) and can be enlarged. The crater volume is due to Arabia Terra being one of the oldest geological formations on Mars, estimated to be 3.7 to 4.1 billion years old. At this time, geological activity inside Mars ended, causing it to lose its planetary magnetosphere and its atmosphere to be slowly eroded by the solar wind.
*A bird’s eye view of a region in Trouvelot Crater. It shows the dark volcanic deposits covering the crater floor and a light mound visible within these deposits. Photo credit: ESA/DLR/FU Berlin*
Much like the Moon’s airless environment has preserved its craters, Mars’ thin atmosphere has ensured that these craters are well preserved. Some of the craters in the image are filled with dark material, while others are filled with lighter sand and undulating dunes. This suggests that some of this sand was deposited on Mars by dust storms, while other material may have been thrown out by the impacts themselves. Others still show signs of collapsing crater walls and worn rims, also indicating wind-induced erosion.
To the left of Trouvelot Crater is an older, more eroded basin with a completely collapsed wall almost entirely covered in dark rock. This material was formed by the wind into the characteristic undulating structures known as “barchan” dunes, characterized by their crescent-shaped profile. Mars Express photographed these dunes at several locations in the northern lowlands and the large Tharsis volcanic region. The dark material, known as “mafic rock,” is rich in minerals and is often associated with volcanism here on Earth.
*Close-up showing the light hill at top left contrasting with the dark rock. Photo credit: ESA/DLR/FU Berlin*
This again indicates that material thrown out by impacts was blown around by the wind and eventually pulled down along the crater walls. The fact that Trouvelot intersects this crater suggests that it is the younger of the two, and the commonality of craters with dark material suggests that the mechanisms involved are ubiquitous on Mars. Amid the dark material is a light hill, about 20 km long, covered in ridges and grooves. Such mounds have been observed in other locations and suggest that other processes may be at work.
One clue is the minerals observed in these mounds, which suggest they formed in the presence of running water. Whether this is the case remains a matter of scientific debate, and there are several possibilities as to how they could have been deposited by water.
Further reading: ESA
