Traces of an ancient system of underground lakes on Mars

Mars basin that could host a lake (Image NASA/JPL-Caltech/MSSS)
Mars basin that could host a lake (Image NASA/JPL-Caltech/MSSS)

An article published in the “Journal of Geophysical Research – Planets” report geological evidence that on planet Mars in ancient times there was a system of interconnected underground lakes and five of them could contain minerals essential for life. A team of researchers used data collected by ESA’s Mars Express space probe to investigate what are now basins, deep craters in the red planet’s northern hemisphere, finding evidence that they once housed lakes.

In recent years, many researches have been conducted to reconstruct the history of the planet Mars that show how it was much more similar to Earth when it was young. Generally, a research focuses on a certain area to study the geological traces left by liquid water flows over 3.5 billion years ago, but occasionally research spans vast territories. In this case, they found 24 craters that have a depth of 4,000 meters and more compared to the arbitrary level equivalent to the Earth’s sea level.

Francesco Salese of the Dutch University of Utrecht, the lead author of this research, explained that he and his colleagues found the first geological evidence of an ancient large-scale presence of groundwater on Mars. The study of these craters has in fact shown features that may have formed only in the presence of water.

This type of crater is formed through an evolution that starts from a basin full of water with canals, valleys and shorelines of the kind that could exist when Mars was young. Four billion years ago it had a magnetic field that protected its atmosphere from solar wind but it’s a planet with a size about half of the Earth’s that cooled down relatively quickly losing that shield and slowly its atmosphere got eroded causing a climate collapse. That had strong effects on water as well: part of it evaporated when the atmospheric pressure went down lowering the water level in the basins also influencing their geological features. Eventually, waterless craters remained that got eroded.

The ancient water levels are aligned with the shorelines proposed for the possible ocean that perhaps existed on Mars at the time. According to Gian Gabriele Ori of the Italian D’Annunzio University, another of the authors of this research, this ocean was perhaps connected to a system of underground lakes that could be present planet-wide about 3.5 billion years ago.

In five of the examined craters traces of clays, carbonates and silicates, compounds linked to the birth of life on Earth, were found, a new confirmation that Mars was a hospitable planet for possible life forms similar to the Earth’s ones. ESA is investigating also with its ExoMars mission, which is being conducted together with the Russian space agency Roscosmos and includes the launch of a new rover in 2020 to carry out on-site surveys in the hope of finding some new clues. The Trace Gas Orbiter, a space probe of the ExoMars mission, is already studying Mars from the orbit. In essence, new information keep on being collected and many more will be collected to reconstruct the history of Mars and try to understand if it ever hosted life forms.

Distribution of ancient lakes, indicated by red dots (Image Topography: NASA/MGS/MOLA; Crater distribution: F. Salese et al (2019))
Distribution of ancient lakes, indicated by red dots (Image Topography: NASA/MGS/MOLA; Crater distribution: F. Salese et al (2019))

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