Dark and volcanic
To the left of Trouvelot Crater sits another basin that appears to be even older and more eroded, with a wall that’s almost completely worn away. Trouvelot cuts through this crater, further indicating that this more deteriorated crater companion was there first.
The floor of this more ancient crater is nearly entirely covered in dark rock, which is rich in minerals such as magnesium, iron, pyroxine and olivine (known as ‘mafic’ rock, and often created by volcanism). These volcanic rocks may have been thrown up by crater-forming impacts, and later moved around as winds swept across the terrain and gravity pulled material down crater walls.
The other large craters seen here – and across Arabia Terra, beyond the edges of this frame – have similar dark deposits on their floors or walls, indicating that these processes are widespread across this part of Mars.
In Trouvelot Crater, the dark material has been shaped by wind into rippling dunes known as ‘barchan’ dunes. These are characteristically sickle- or crescent-shaped, and created when winds predominantly blow in one direction. Mars Express has spotted barchan dunes on Mars before, such as in the planet's north polar region and near the large volcanic province of Tharsis.