Long after the solar wind had stripped Mars of its atmosphere, turning it into the cold, arid world it is today, lakes of water still existed on the surface of the planet. According to a new study published in the Journal of Geophysical Research: Planets, the red planet had several lakes and snowmelt-fed streams between 2 and 3 billion years ago — roughly a billion years after its original “wet era” is believed to have come to an end.

What this means is that Mars may have been host to microbial life for a much longer time than scientists had hitherto believed possible.

“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,” Rich Zurek, the Mars Reconnaissance Orbiter (MRO) project scientist at NASA’s Jet Propulsion Laboratory, said in a statement released Thursday. “This paper presents evidence for episodes of water modifying the surface on early Mars for possibly several hundred million years later than previously thought.”

For the purpose of this study, researchers analyzed high-resolution images of Mars' northern Arabia Terra region snapped by cameras on board the MRO. When they compared these images with data collected by NASA’s Mars Global Surveyor and the European Space Agency's Mars Express, they found clear evidence, such as fresh shallow valleys, that there was a considerable amount of water on the landscape 2 to 3 billion years ago.

pia20837_pressimage1_valley Streamlined forms in this Martian valley resulted from the outflow of a lake hundreds of millions years more recently than an era of Martian lakes previously confirmed. This image from the Context Camera on NASA's Mars Reconnaissance Orbiter covers an area in Arabia Terra about 8 miles wide. Photo: NASA/JPL-Caltech/MSSS

The estimated rate at which water flowed through these valleys is consistent with runoff from melting snow, suggesting that the seasonal melting of snow, not rain, was responsible for the creation of this water.

“One of the lakes in this region was comparable in volume to Lake Tahoe,” lead author Sharon Wilson, from the Smithsonian Institution, Washington, and the University of Virginia, Charlottesville, said in the statement, referring to the California-Nevada lake that holds about 45 cubic miles of water. “This particular Martian lake was fed by an inlet valley on its southern edge and overflowed along its northern margin, carrying water downstream into a very large, water-filled basin we nicknamed ‘Heart Lake.’”

The researchers calculated that this lake may once have held about 670 cubic miles of water — more than Lake Ontario, which is one of North America’s Great Lakes. Moreover, the presence of valleys both north and south of the Martian equator suggests that the seasonal presence of water during this period was a global, rather than a regional, phenomenon.

However, further studies would be needed to understand the exact mechanism that allowed the planet to warm up enough to allow an interval when flowing water existed on its largely frozen surface.