This illustration depicts a lake partially filling Mars' Gale Crater, receiving runoff from snow melting on the crater's northern rim. (NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS)

New information from NASA's Curiosity Rover suggests that Mars may once have had large, long-lasting lakes above ground. That would challenge the more popular theory that water on the planet was only underground, or only appeared in a few areas for a short amount of time.

The key to this latest theory is Mount Sharp, which stands 3 miles tall and sits in the red planet's Gale Crater. But Mount Sharp is a curious formation: The layered mountain is made of different kinds of sediment. Some layers were probably deposited by a surrounding lake bed, and other seem more likely to be the result of river or wind deposits.

An illustration of Gale Crater filling with sediment from deltas, wind, and lake deposits, then later being eroded by the wind. (NASA/JPL-Caltech)

Now, NASA scientists believe that a large lake in the Gale Crater — or even a series of lakes that evaporated and then reformed — caused the mountain's unusual formation.

To have liquid water on the surface, Mars would have had a much warmer, heavier atmosphere than it does now. NASA scientists still aren't sure how that atmosphere formed, or why it changed. But based on Curiosity's readings around the Murray formation — a section of rock 500 feet high — it seems that the crater lake filled with sediment (carried in by rivers) over and over. Once this sediment reached a certain height, the hardened sediment was eroded by wind, eventually forming the mountainous shape we now see.

"The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works," Curiosity Project Scientist John Grotzinger said in a statement. "As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year."

Liquid water on the surface would be a big deal, giving scientists a greater hope of finding signs of past life on the planet. But for now, NASA researchers don't have enough data to know exactly how long the water was around— or whether the spark of life happened to ignite during that time.

New findings from the Curiosity Rover suggest that Mars might have once had large lakes on its surface. (NASA Jet Propulsion Laboratory)