* Astronomy

Reull Vallis: a river ran through it

ESA's Mars Express imaged the striking upper part of the Reull Vallis region of Mars with its high-resolution stereo camera last year.
Reull Vallis, the river-like structure in these images, is believed to have formed when running water flowed in the distant martian past, cutting a steep-sided channel through the Promethei Terra Highlands before running on towards the floor of the vast Hellas basin.
Read more