On Mars, over a mile wide and 650 feet deep, dramatic desiccated river channels were discovered, showing how the Red Planet used to be on its surface with liquid water.
We know Mars today as a barren wasteland, but about 3.4 billion years ago, the Red Planet was flooded in blue and was characterized by a large ocean in the Northern Hemisphere, lakes and many meandering rivers. In its ancient past, Mars had a thick, warm atmosphere that allowed the planet to keep liquid water on the surface. Observations of orbiting satellites around Mars and rovers on the surface have proven this, whether in the form of parched river beds or clay-like deposits that required the formation of water.
Eventually, the thick Martian atmosphere and thus also the surface water of the planet evaporated. Visible evidence of this water can still be seen as frozen ice at the poles.
New images published today by the European Space Agency (ESA) provide further evidence of the watery past of Mars. The region shown in the photos is a valley system in the southern highlands, east of a large impact crater called Huygens. The photos taken by ESA's Mars Express satellite late last year show an ancient, heavily cratered region that still has the telltale signs of running water despite eons of erosion.
The water flowed from the north (from right to left) down the photo), which, according to ESA, produced rivers of up to two kilometers wide and 200 meters deep. Today, the valley is smooth and fragmented, but its former status as a riverbed is clearly visible. The ESA further explains:
Overall, the valley system appears to branch out significantly, forming a pattern resembling a tree reminiscent of tree trunks emanating from a central trunk. This type of morphology is called "dendritic" – the term derives from the Greek word for tree (Dendron), and it's easy to see why. Different channels split off the central valley and form small tributaries, which often split again on their outward journey.
This type of dendritic structure can also be found in drainage systems of the earth. A particularly good example is the river Yarlung Tsangpo, which meanders from its source in western Tibet through China, India and Bangladesh. In the case of this image of Mars, these branched canals were probably formed by surface water resulting from a once-powerful river stream with heavy rains. It is believed that this river has severed existing terrain on Mars, breaking new ground and creating a new landscape.
The presence of ancient water on Mars raises many questions. What was the source of this rushing water? Was it caused by melting glaciers, or was it water spilling below the surface? Or has rain produced the running water? And how long did this water last? Did this water contribute significantly to the habitable conditions on Mars and did life once appear on the planet?
These questions remain unanswered and serve as a scream for further investigations of Mars. Fortunately, NASA's curiosity rover and InSight lander continue to collect valuable data, as well as NASA's Mars Reconnaissance Orbiter, the ExoMars Trace Gas Orbiter, and the ESA's Mars Express. We are also looking forward to the upcoming ExoMars mission, which the newly named Rosalind Franklin Rover will encounter.