As we look at the numerous graben and valleys that wind through
the Martian highlands, it is not always clear which geological
processes created them. Some valleys have very similar
characteristics to those on Earth carved out by the flow of
surface water; others possess a morphology where this is not so
obvious. These images, acquired by the High Resolution Stereo
Camera (HRSC) operated by the German Aerospace Center (Deutsches
Zentrum für Luft- und Raumfahrt; DLR) on board ESA’s Mars
Express spacecraft, show the upper reaches of the Reull Vallis
region, a valley that was, at times, shaped by the flow of
glacial ice. Reull Vallis is an outflow channel stretching over
1500 kilometres across the massifs of Promethei Terra, in the
highlands of Mars' southern hemisphere, towards Hellas Planitia,
an impact basin that, with a diameter of almost 2300 kilometres,
is the largest impact structure on our planetary neighbour. The
High Resolution Stereo Camera (HRSC) on Mars Express has been
used numerous times to acquir