Mars once had a vast ocean covering a third of its surface, according to scientists, increasing the chances that life may once have existed there.
Scientists from Northern Illinois University and the Lunar and Planetary Institute in Houston used a new computer program to produce a more detailed global map of the valley networks on Mars. The findings indicate the networks are more than twice as extensive as had been previously depicted.
Further, the regions with the most valley networks form a belt around the planet between the equator and mid-southern latitudes, consistent with a history of precipitation and the presence of a large ocean in the northern hemisphere.
Scientists have previously hypothesized that a single ocean existed on ancient Mars, but the matter has been hotly debated.
“All the evidence gathered by analyzing the valley network on the new map points to a particular climate scenario on early Mars,” NIU Geography Professor Wei Luo said. “It would have included rainfall and the existence of an ocean covering most of the northern hemisphere, or about one-third of the planet's surface.”
Since Mars' valley networks were discovered in 1971 by the Mariner 9 spacecraft, scientists have debated whether they were created by erosion from surface water, which would point to a climate with rainfall, or through a process of erosion known as groundwater sapping which occurs in cold, dry conditions.
The large disparity between river-network densities on Mars and Earth had provided a major argument against the idea that runoff erosion formed the valley networks. But the new mapping study reduces this disparity, indicating some regions of Mars had valley network densities more comparable to those found on Earth.
“It is now difficult to argue against runoff erosion as the major mechanism of Martian valley network formation,” Luo said.
The findings appear in the current issue of the Journal of Geophysical Research — Planets.