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Water on Mars may have flowed for billions of years longer than previously thought.

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  • Tip Bones

According to observations from a long-running Mars mission, liquid water may have flowed on the Red Planet as recently as 2 billion years ago, much later than scientists previously assumed.

Scientists used years of data from NASA's Mars Reconnaissance Orbiter (MRO), which has been orbiting the Red Planet since 2006, to map the prevalence of chloride salt deposits left behind by flowing water.

Using the "crater counting" method, the scientists interpreted a younger age for the salt deposits by analysing dozens of photos of salt deposits taken by the spacecraft's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). The fewer craters a location should have, with adjustments for factors such as a planet's atmosphere, allow scientists to determine its age.

Based on the observations, the new findings stretch the existence of water on Mars from 3 billion years ago to as recently as 2 billion years ago, which could have consequences for life on Mars and, more broadly, the planet's geological history.

"Part of the benefit of MRO is that our vision of the globe continues to improve over time," said Leslie Tamppari, MRO's deputy project scientist at NASA's Jet Propulsion Laboratory, in a statement. "The more of the world we map with our equipment, the greater our understanding of its history."

Elevation maps were also constructed using the MRO's wide-angle context camera and the zoomed-in images given by the High-Resolution Imaging Science Experiment (HiRISE), which can see craters as small as the Curiosity or Perseverance Mars rovers.

The salt minerals were discovered 14 years ago by a different spacecraft named Mars Odyssey, although MRO has greater resolution instruments than its older (and still operating) cousin in orbit.

A study based on the research was published in AGU American Geophysical Union Advances on December 27, 2021. Ellen Leask, who completed much of the work during her doctoral studies at the California Institute of Technology, led the study. Bethany Ehlmann, a planetary scientist at the same institution, is her supervisor and co-author.

In recent years, scientists have conducted a slew of investigations to determine the extent of flowing water on Mars, both on the ground and using orbital data. Just a few days ago, a presumed subterranean water reservoir at Mars' southern pole was disproved using new data interpretations.