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Water on Mars may have flowed for a billion years longer than thought

This image from NASA's Mars Reconnaissance Orbiter shows the Bosporos Planum plain on the Red Planet. The white specks are salt deposits found within a dry channel, a clue to its watery past.
This image from NASA's Mars Reconnaissance Orbiter shows the Bosporos Planum plain on the Red Planet. The white specks are salt deposits found within a dry channel, a clue to its watery past. (Image credit: NASA/JPL-Caltech/MSSS)

Observations by a long-running Mars mission suggest that liquid water may have flowed on the Red Planet as little as 2 billion years ago, much later than scientists once thought.

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

By studying dozens of images of salt deposits taken by the spacecraft's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), the scientists interpreted a younger age for the salt deposits using a method "crater counting." The younger a region is, the fewer craters it should have, with adjustments for aspects such as a planet's atmosphere, allowing scientists to estimate its age.

The new results push forward the existence of water on Mars from 3 billion years ago to as little as 2 billion years ago, based on the observations, which could have implications for life on Mars and more broadly, the planet's geological history.

"Part of the value of MRO is that our view of the planet keeps getting more detailed over time," Leslie Tamppari, MRO's deputy project scientist at NASA's Jet Propulsion Laboratory, said in a statement. "The more of the planet we map with our instruments, the better we can understand its history."

Related: Scientists spot water ice under the 'Grand Canyon' of Mars

An artist's illustration of NASA's Mars Reconnaissance Orbiter in orbit around the Red Planet. (Image credit: JPL/NASA)

The scientists also created elevation maps using MRO's wide-angle context camera, and the zoomed-in views provided by the High-Resolution Imaging Science Experiment (HiRISE) that can spot craters as small as the Curiosity or Perseverance Mars rovers. 

The salt minerals were first spotted by a different spacecraft 14 years ago, called Mars Odyssey, but MRO's advantage is it has higher resolution instruments than its older (and still operational) companion in orbit.

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

Scientists have performed numerous studies in recent years to assess the extent of flowing water on Mars, both up close through surface missions and using orbital data. Just days ago, a suspected underground reservoir of water at the Martian southern pole was debunked using new interpretations of the data.

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Elizabeth Howell
Elizabeth Howell

Elizabeth Howell, Ph.D., is a contributing writer for Space.com since 2012. As a proud Trekkie and Canadian, she tackles topics like spaceflight, diversity, science fiction, astronomy and gaming to help others explore the universe. Elizabeth's on-site reporting includes two human spaceflight launches from Kazakhstan, and embedded reporting from a simulated Mars mission in Utah. She holds a Ph.D. and M.Sc. in Space Studies from the University of North Dakota, and a Bachelor of Journalism from Canada's Carleton University. Her latest book, NASA Leadership Moments, is co-written with astronaut Dave Williams. Elizabeth first got interested in space after watching the movie Apollo 13 in 1996, and still wants to be an astronaut someday.