Frosty martian valleys
Nestled within the fractured rim of a vast impact basin on Mars are valley floors dusted in frost.
At 2200 km wide and up to 9 km deep, the Hellas Basin is the largest impact crater on Mars. This scene, captured on 6 December 2015 by ESA’s Mars Express, focuses on a portion of the western rim of the basin.
This region spans a height difference of over 6000 m, stepping down like a staircase from the basin’s fractured, terraced rim to its flat, low-lying floor that is covered in frost or ice.
The surface expression of numerous valley-like features can be seen below the icy covering, indicating a flow of material towards the catchment areas on the floor of Hellas.
For example, towards the centre of the image, a glacier-like flow has carved a valley through the terraced topography, transporting and dumping material into the basin in a fan structure.
Zooming into the channel reveals parallel structures on the surface – ‘lineated valley fill’– that point to the flow of material.
Mass-movement of material can be seen all over the scene. Another example can be found in the small impact crater to the far left of the main image: its rim has been breached, and material has cascaded downhill.
Elsewhere, numerous gullies can be seen etched all along the terraced slopes.
Towards the centre-right of the main images are neighbouring impact craters that have been cross-cut by a fault, creating a small step in the terrain that can be best seen in the 3D anaglyph image.