ESA satellite images show ancient signs of water flows on Martian surface

While Mars is seen as a cold, dry world, evidence based on past research suggests that the planet once had a thicker, denser atmosphere that was able to lock in far greater amounts of warmth, and therefore facilitate and support the flow of liquid water on the surface below.

The images sent by Mars express show clear signs of past water flows across the Martian surface. This latest image shows one such region: a system of valleys in the southern highlands of Mars, located east of a large, well-known impact crater called Huygens and north of Hellas, the largest impact basin on the planet. At 3.5 to four billion years old, the southern highlands are some of the oldest and most heavily cratered parts of Mars, with many signs of ancient water flow observed here, according to ESA.

“The topography of the region suggests that water flowed downhill from the north to the south, carving out valleys up to two kilometres across and 200 metres deep as it did so. These valleys as they stand today, have undergone significant and heavy erosion since they were formed. This erosion is visible in the form of broken down, smoothed, fragmented and dissected valley rims, especially in the valleys cutting from east to west.

“Overall, the valley system appears to branch out significantly, forming a pattern a little like tree branches stemming from a central trunk,” the ESA said.

This kind of morphology is known as ‘dendritic’ a term derived from the Greek word for tree (dendron). Various channels split off from the central valley, forming little tributaries that often split again on their journey outwards.

This dendritic structure is also seen in drainage systems on Earth. A particularly good example is that of the Yarlung Tsangpo river (Brahmaputra in India), which snakes its way from its source in western Tibet down through China, India, and Bangladesh. 

While it is unclear where all of this water came from originally – precipitation, groundwater, melting glaciers? – all of this required a far warmer and more watery past for Mars than the planet we see today, the ESA said.

This raises the question of the warmer and wetter climate providing conditions suitable for life. Next year, ESA and Roscosmos will launch the ExoMars mission comprising a rover – recently named Rosalind Franklin – and a surface science platform. The rover will drive to interesting locations to drill below the surface in search for signs of life – the first mission of its kind. 

Meanwhile, the ExoMars Trace Gas Orbiter continues to analyse the atmosphere in greater detail than ever, with a particular interest for gases potentially related to biological or geological activity, and to identify subsurface locations where water-ice or hydrated minerals are present.

As the next step, ESA together with international partners are considering returning a sample of Mars to Earth – an ambitious task that will provide scientific treasures for generations to come.