ESA has released images of the Acheron Fossae region on Mars (Top image ESA/DLR/FU Berlin (CC BY-SA 3.0 IGO)) captured by its Mars Express space probe’s High Resolution Stereo Camera (HRSC). The peculiarity of these images is that they show the two faces of Mars, meaning that they show how the red planet is basically divided into two parts with very different geological characteristics. About half of Mars is composed of an ancient terrain marked by craters and other signs of age and activity, while the other half is much smoother, with a surface probably reshaped by lava from volcanoes that are no longer active.
Among the topics of study carried out in the reconstruction of the history of Mars is the search for the reasons for the differences in the appearance of the two halves of the planet. In ancient times, this planet was much more active from a geological point of view. Even today, colossal volcanoes can be seen, such as Olympus Mons, the largest volcano in the solar system, located about 1,200 kilometers south (on the left in the image) of Acheron Fossae.
These volcanoes have certainly shaped the landscape with their eruptions. In the center of the image, you can still see the traces of an impact crater now partially covered by lava that probably came from Alba Mons, another volcano to the northeast (bottom right in the image) of Acheron Fossae.
In the right side of the image there’s a system of geological formations of the horst-and-graben type, an alternation of raised and lowered fault blocks. They were formed about 3.7 billion years ago as parallel blocks of planetary crust that were deformed in various ways over time until they took on the current appearance in which there’s an alternation of raised and lowered fault blocks. Geologists are familiar with the topography of horst-and-graben systems because they exist on Earth as well.
The smoother part in the lower center of the image represents the beginning of younger plains that move away from Acheron Fossae. Near the grabens, the plains are marked by the traces of moving glaciers containing rocks. It’s not clear whether the rocks were picked up by the moving glaciers, or they originally covered them, or both occurred.
Today, the large volcanoes of Mars are no longer active, so the effects that their eruptions had on the red planet must be reconstructed through the traces they left. The entire area around Acheron Fossae shows different traces of various geological activities and impacts that created craters. For this reason, it’s an area that keeps on being studied, and every new detail captured by space probes orbiting Mars can help improve this reconstruction.
