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Mars today is a cold, dry world, but it may not always have been so. Recent studies increasingly indicate 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. While this is no longer the case, planetary researchers see clear signs of past water activity tracing across the Martian surface. New images from ESA’s Mars Express orbiter show one such region: a branching, desiccated system of trenches and 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.
This image from ESA’s Mars Express shows a network of dried-up valleys on Mars, and comprises data gathered on November 19, 2018. North is to the right. Image credit: ESA / DLR / FU Berlin / CC BY-SA 3.0 IGO.
“Today, it is thought that climate change took place on Mars about 3.7 to 3.8 billion years ago, when environmental conditions changed from a somewhat neutral, potentially life-sustaining and sporadically humid environment to a much more acidic, dry, cold environment that is hostile to life,” explained Dr. Ralf Jaumann, a researcher in the DLR Institute of Planetary Research and principal investigator of Mars Express’ High Resolution Stereo Camera.
“The main reason for this, according to current knowledge, was the gradual loss of the Martian atmosphere and a change in the planet’s volcanic activity.”
“This climate change transformed our neighboring planet from being a one with temporary rivers and lakes that was, so to speak, ‘full of hope’ as regards the possible emergence and development of life, into a one that was just dry and salty.”
One of the reasons why Mars lost its atmosphere is the loss of its magnetic field, which was active during the first 500 million years.
“As it grew ever weaker the solar wind was able to gradually split the molecules in the atmosphere, and the resultant ions were accelerated and lost to space. As a result, and also due to the declining volcanism, the atmosphere became thinner and thinner,” Mars Express team members said.
“In addition, Mars is only half the size of Earth, so its gravitational force is barely sufficient to bind atmospheric molecules to it.”
“Below a certain atmospheric pressure, water can no longer remain liquid on the surface of a planet — it can remain as ice or gas.”
“The lack of precipitation on Mars ultimately collapsed the water cycle.”
This image from ESA’s Mars Express shows a valley network on Mars. This oblique perspective view was generated using a digital terrain model and Mars Express data gathered on November 19, 2018. Image credit: ESA / DLR / FU Berlin / CC BY-SA 3.0 IGO.
At 3.5-4 billion years old, the southern highlands of Mars are some of the oldest and most heavily cratered parts of the planet, with many signs of ancient water.
The topography of this region suggests that water flowed downhill from the north to the south, carving out valleys up to 1.2 miles (2 km) across and 656 feet (200 m) deep as it did so.
“We see these valleys as they stand today, having undergone significant and heavy erosion since they were formed,” the researchers said.
“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.
“This kind of morphology is known as ‘dendritic’ — the term is derived from the Greek word for tree (dendron), and it is easy to see why,” the scientists explained.
“Various channels split off from the central valley, forming little tributaries that often split again on their journey outwards.”
This kind of dendritic structure is also seen in drainage systems on Earth.
“A particularly good example is that of the Yarlung Tsangpo river, which snakes its way from its source in western Tibet down through China, India, and Bangladesh,” the researchers said.
“In the case of this image of Mars, these branching channels were likely formed by surface water runoff from a once-strong river flow, combined with extensive rainfall.”
“This flow is thought to have cut through existing terrain on Mars, forging new paths and carving a new landscape.”
“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.”
