Mars had large rivers long after the planet lost most of its atmosphere to space, a new study suggests. That great thinning, which was driven by air-stripping solar particles, was mostly complete by 3.7 billion years ago, leaving Mars with an atmosphere far wispier than Earth’s, space.com reports. But Martian rivers likely didn’t totally dry out until less than 1 billion years ago, the new study found. And these waterways were big — wider, on average, than those on Earth. “We can start to see that Mars didn’t just have one wet period early in its history and then dried out,” study lead author Edwin Kite, an assistant professor of geophysical sciences at the University of Chicago, told Space.com.
“It’s more complicated than that; there were multiple wet periods. It’s unclear how much water Martian rivers carried, because their depth is hard to estimate. Determining depth generally requires up-close analysis of riverbed rocks and pebbles, Kite said, and such work has only been done in a few locations on Mars, such as Gale Crater, which NASA’s Curiosity rover has been exploring since 2012.
The ancient Mars rivers didn’t flow in just a few favored spots; rather, they were distributed widely around the planet, Kite and his colleagues found.