Plan view of Nirgal Vallis (ESA)

10 October 2019

The European Space Agency has published data from the Mars Express orbiter, which shows, more convincingly than ever before, that water flowed on Mars in the past. A clear river vally system can be seen. Mars may seem to be an alien world, but many of its features look eerily familiar – such as this ancient, dried-up river system that stretches out for nearly 700 kilometres across the surface, making it one of the longest valley networks on the planet.

The area of Mars shown in these new images from ESA’s Mars Express spacecraft lies just south of the planet’s equator, and is known to have been shaped by a mix of flowing water and impacts: events where rocks sped inwards from space to collide with the martian surface.

Both of these mechanisms are visible here: a number of impact craters, some large and some small, can be seen speckled across the ochre, caramel-hued surface, and a tree-like, forked channel cuts prominently through the centre of the frame.

This ancient valley system is named Nirgal Vallis, and was once filled with running water that spread across Mars. By exploring the characteristics of the surrounding craters, scientists estimate the system’s age to be between 3.5 and 4 billion years old.