ESA has published an image (ESA/DLR/FU Berlin. CC BY-SA 3.0 IGO) captured by its Mars Express space probe’s High Resolution Stereo Camera (HRSC) instrument of Aganippe Fossa, a formation that has the appearance of a scar on the surface of the planet Mars which is truly colossal given that it’s approximately 600 kilometers long. This rift valley is a geological formation of the type called graben in jargon. There are no certainties about its formation but it’s probably linked to lava flows under the enormous volcanoes of the Tharsis region, starting with Arsia Mons, the closest to Aganippe Fossa.
For over twenty years, the Mars Express space probe has been observing the planet Mars from its orbit. On December 13, 2023, its HRSC camera took several photos of Aganippe Fossa, a graben decidedly out of the ordinary given its length of about 600 kilometers. The Tharsis region has been the subject of studies for many years due to the presence of large volcanoes such as Olympus Mons. The volcano closest to the giant scar of Aganippe Fossa is Arsia Mons, over 9 kilometers high and with a diameter of 435 kilometers.
The volcanic activity of a now distant past is considered by researchers to be the most likely origin of Aganippe Fossa. According to this reconstruction, the rising magma under the mass of the large volcanoes in the Tharsis region led the Martian crust to stretch and then break. The Arsia Mons volcano probably ceased activity around 50 million years ago, yet the colossal scar we see today may still show the consequences of magma flows from that and other Tharsis volcanoes.
The topographic view at the bottom (ESA/DLR/FU Berlin. CC BY-SA 3.0 IGO) shows the differences in altitude in the Aganippe Fossa area due precisely to the proximity of Arsia Mons. The left half is bumpy, full of irregularities created by small clustered mounds, jagged grooves, and ridges. The right half is smoother due to wind erosion. Precisely the action of the wind left zebra stripes due to the fact that darker materials are deposited on lighter ground or vice versa.
The geological complexity of the area brings some uncertainty regarding the origin of Aganippe Fossa. The proximity to the large volcanoes of Tharsis increases the interest in this very long scar by scientists from various disciplines who will continue to study this region of Mars.
