Signs of ancient flowing water on Mars
ESA’s Mars Express has returned images of a region on the Red Planet that appears to have been sculpted in part by flowing liquid. This again adds to the growing evidence that Mars had large volumes of water on its surface in the distant past.
On 21 June last year, Mars Express pointed its high-resolution stereo camera at the western part of Acidalia Planitia, a gigantic basin in the planet’s northern lowlands, at the interface with Tempe Terra, an older, higher terrain. Acidalia Planitia is a region so vast that it can be seen from Earth by amateur astronomers.
The images taken cover part of the western edge of the region, where some of the numerous valleys descending from Tempe Terra show subtle evidence for ‘dendritic’ drainage patterns emanating from them. The channels in the images are believed to have been formed by the surface run-off of flowing water from rain or melting snow during some distant martian epoch.
The lower-left part of the image appears to be in shadow, but this darkening is in fact is due to differences in surface material: the left-hand side is covered with dark sand, probably of volcanic origin, while the right side is covered with brighter dust.