In keeping with that analysis, 22 of the 66 networks evaluated the best match the patterns formed by meltwater running under a glacier, the researchers concluded. Another nine best match patterns formed by glaciers themselves, while 14 best match patterns formed by rivers. Most of the rest weren’t distinct enough matches for a specific formation scenario.
The researchers also found that the valleys that looked like they were formed by meltwater running beneath glaciers were spread across Mars, while those that looked to have been formed by rivers were concentrated around Arabia Terra, a particularly old region of Mars, according to NASA.
Rivers and the melted water slipping below a glacier imply one key difference about their environment: temperature. The scientists argue that their new research matches well with recent theories that Mars may have been cooler in its faraway past than other hypotheses have suggested.
“For the last 40 years, since Mars’s valleys were first discovered, the belief was that rivers once flowed on Mars, eroding and originating all of these valleys,” Grau Galofre said. “We tried to put everything together and bring up a hypothesis that hadn’t really been considered.”
The research is described in an article published on Monday (Aug. 3) in the magazine Nature Geoscience.