Washington, Sep 16 Lakes and snowmelt-fed streams on Mars formed much later than previously thought possible, new research has found.
The recently discovered lakes and streams appeared roughly a billion years after a well-documented, earlier era of wet conditions on ancient Mars, the study said.
These results provide insight into the climate history of the Red Planet and suggest the surface conditions at this later time may also have been suitable for microbial life.
"We discovered valleys that carried water into lake basins," said Sharon Wilson of the Smithsonian Institution, Washington, and the University of Virginia, Charlottesville.
"Several lake basins filled and overflowed, indicating there was a considerable amount of water on the landscape during this time," Wilson noted.
Wilson and colleagues found evidence of these features in Mars' northern Arabia Terra region by analysing images from the Context Camera and High Resolution Imaging Science Experiment camera on NASA's Mars Reconnaissance Orbiter and additional data from NASA's Mars Global Surveyor and the European Space Agency's Mars Express.
To bracket the time period when the fresh shallow valleys in Arabia Terra formed, scientists started with age estimates for 22 impact craters in the area.
They assessed whether or not the valleys carved into the blankets of surrounding debris ejected from the craters, as an indicator of whether the valleys are older or younger than the craters.
They concluded that this fairly wet period on Mars likely occurred between two and three billion years ago, long after it is generally thought that most of Mars' original atmosphere had been lost and most of the remaining water on the planet had 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," Mars Reconnaissance Orbiter Project Scientist Rich Zurek of NASA's Jet Propulsion Laboratory, Pasadena, California, said.
"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," Zurek said.
The findings were reported in the Journal of Geophysical Research, Planets.