On top of trying to figure out if Mars currently has liquid water somewhere, scientists are also trying to answer the question of how long liquid water was on Mars and when it disappeared – or went underground. We know there was water. There are river and stream channels, gullies, and even sedimentary rocks on Mars that tell us there was water. Previous estimates had the disappearance dating back about 3 billion years.

Now, imagery and data from the Mars Reconnaissance Orbiter have found evidence that liquid water was still on the surface about 2 to 2.5 billion years ago, giving water another billion years or so to provide some of the necessary requirements for life. And they found this evidence by looking at salt deposits left behind in the depressions of long ago ponds on volcanic plains.

The scientists analyzed images by counting craters, which tells us how old the terrain is – more craters equals older terrain underneath. And from their crater counts, they derived the approximate age of the volcanic plains which means the ponds had to be younger than that. Pretty cool, huh? Our Mars missions are working hard, day after day, year after year, to collect amazing data.

This work was published in AGU Advances with lead author Ellen Leask.

More Information

NASA JPL press release

“Evidence for Deposition of Chloride on Mars From Small-Volume Surface Water Events Into the Late Hesperian-Early Amazonian,” Ellen K. Leask and Bethany L. Ehlmann, 2021 December 27, AGU Advances