June 5 (UPI) -- What was once one of our solar system's preeminent mysteries -- whether or not Mars once hosted water -- is now accepted as fact.
Today, planetary scientists are more interested in determining how long water was present on the Martian surface and how much was there.
In a new study, researchers at Northern Illinois University decided to use the Red Planets' valleys and weathered canyons as a measuring stick for determining how much water once flowed across the surface of Mars.
Researchers believe water once evaporated from large Martian oceans and returned the planet's surface as rain. As rain flowed back to ocean basins, it eroded the planet's surface. Scientists asked themselves: How much water did it take to erode the planet's 3-billion-year-old valleys?
"Our most conservative estimates of the global volume of the Martian valley networks and the cumulative amount of water needed to carve those valleys are at least 10 times greater than most previous estimates," Wei Luo, a geography professor at NIU, said in a news release.
The predictive model developed by Luo and his colleagues showed the amount of water necessary to carve the Red Planet's ancient valley system is 4,000 times the volume of the valleys themselves.
"That means water must have recycled through the valley systems on Mars many times, and a large open body of water or ocean is needed to facilitate such active cycling," Luo said. "I would imagine early Mars as being similar to what we have on Earth -- with an ocean, lakes, running rivers and rainfall."
As usual, the research -- published in the journal Nature Communications -- presents new problems. The amount of water estimated by the model doesn't jive with models simulating the ancient Martian climate. Currently, scientists don't believe Mars was ever warm enough to encourage such a dynamic hydrological cycle.
"Mars is much farther way from the sun than Earth, and when the sun was younger, it was not as bright as it is today," Luo said. "So there's still a lot to work out in trying to reconcile the evidence for more water."