Acheron Fossae is marked by large, deep cracks on the surface known as ‘fossae’. These linear depressions are a textbook example of what’s called a ‘horst and graben’ landscape – a pattern of raised and lowered blocks of crust. The formation of such a structure is driven by the planet’s internal geological activity, where hot mantle material from deep inside rises toward the surface – a process known as mantle upwelling. This causes the ground to stretch and pull apart, leading blocks of crust to sink down (graben) relative to the neighboring higher blocks (horst). Since Mars was most geologically active during the Noachian period, around 3.7 to 3.9 billion years ago, Acheron Fossae likely formed in that period. Over time, many of these grabens have been filled with different types of material, especially deposits rich in ice.