The computer-generated map, based on topographic data from NASA satellites, shows a vast ocean in the north and valleys around the equator. It also shows that Mars' network of valleys is at least twice as extensive as previously estimated.
"The relatively high values over extended regions indicate the valleys originated by means of precipitation-fed runoff erosion -- the same process that is responsible for formation of the bulk of valleys on our planet," said Wei Luo, geography professor at Northern Illinois University, in a statement.
Luo said that rain "would be mostly restricted to the area over the ocean and to the land surfaces in the immediate vicinity, which correlates with the belt-like pattern of valley dissection seen in our new map."
NASA's Mariner 9 space probe first discovered the ancient Martian valley networks in 1971, but scientists have debated whether the valleys were the result of water erosion -- suggesting humidity and rainfall -- or groundwater sapping erosion, which can happen in cold and dry conditions.
The report appears in the Journal of Geophysical Research.
This post was originally published on Smartplanet.com