This Article is part of The Red Planet, our series on Mars. {alertSuccess}
According to a new study, water flowed on Mars as recently as 2 billion to 2.5 billion years ago, which is much more recent than previously imagined.
Caltech (California Institute of Technology) researchers utilized NASA's Mars Reconnaissance Orbiter to discover that liquid water on Mars' surface left salt minerals as recently as 2 billion years ago.
As cold meltwater pouring across the Martian terrain evaporated, chloride salt deposits were left behind.
NASA's Mars Odyssey orbiter, which launched in 2001, detected the salt crystals for the first time 14 years ago.
MRO, which has higher-resolution equipment than Odyssey, was launched in 2005 and has been researching the salts, among other things, on Mars since then.
Previously, it was considered that Mars' liquid surface water evaporated around 3 billion years ago, but the new findings push that back by up to a billion years.
Ellen Leask and Bethany Ehlmann, both of Caltech's Division of Geological and Planetary Sciences, undertook the new research.
The researchers examined images taken by the Mars Reconnaissance Orbiter of sodium chloride (table salt) deposits (MRO).
Leask and Ehlmann discovered several of the salts in depressions originally home to tiny ponds on gently sloping volcanic plains, using both cameras to construct digital elevation maps.
Nearby, the scientists discovered twisting, dry channels — old streams that formerly fed surface runoff (from ice or permafrost thawing) into these ponds.
They were able to date the deposits using crater counting and indications of salts on top of volcanic landscape. In general, the younger a landscape is, the fewer craters it has. Scientists can estimate the age of an area of the surface by counting the number of craters on it.
Chloride salt deposits on Mars are 'interesting,' according to the researchers, because they dissolve quickly and thereby record the last stage of liquid water on the planet's surface.
'Salt is highly soluble,' said Leask, who is now a postdoctoral scholar at Johns Hopkins University's Applied Physics Laboratory.
'As a result, these deposits were created during the evaporation of the planet's last large-scale water.'