Scientists believe that a newly-discovered series of lakes and streams on Mars formed a billion years after a documented era of wet conditions.
The data suggests microbes could have survived on the surface during this later period too, indicating potential for two distinct periods of Martian life.
“We discovered valleys that carried water into lake basins,” said Sharon Wilson of the Smithsonian Institution, Washington. “Several lake basins filled and overflowed, indicating there was a considerable amount of water on the landscape during this time.”
The astronomers were analysing data primarily from NASA’s Mars Reconnaissance Orbiter as it passed over the planet’s northern region.
Researchers believe the series of lakes and valleys ran over a distance of about 90 miles. One lake, nicknamed Heart Lake, contained as much water as some of North America’s Great Lakes, researchers calculated.
To date the features, scientists estimated the ages of 22 impact craters in the area. If the valleys cut into the debris ejected by the craters, they knew they must have come after the meteors fell.
The research team concluded that this “fairly wet period” occurred two to three billion years ago, considerably later than when scientists previously thought most of the red planet’s original atmosphere was lost and the remaining water frozen.
“A key goal for Mars exploration is to understand when and where liquid water was present in sufficient volume to alter the Martian surface and perhaps provide habitable environments,” said Mars Reconnaissance Orbiter Project Scientist Rich Zurek.
He added: “This paper presents evidence for episodes of water modifying the surface on early Mars for possibly several hundred million years later than previously thought, with some implication that the water was emplaced by snow, not rain.”