A far denser atmosphere may have allowed Earth-like oceans to flourish on Mars billions of years ago, the Telegraph reports. Analyzing data from the Mars rover Spirit, Professor Josef Dufek of Georgia Tech University concluded that the planet's atmosphere was once 20 times denser—perfect for harboring lots of water. "Our study is consistent with growing research that early Mars was at least a transiently watery world with a much denser atmosphere than we see today," says Dufek.
Dufek's team examined the mark left by a flying Martian rock during a volcanic eruption about 3.5 billion years ago, LiveScience reports. Judging by the mark's depth, the rock must have flown at less than 43 yards per second—which requires a much denser Martian atmosphere. Talk of water on Mars isn't exactly new: Last year, the Spirit rover found a light-colored rock that hinted at water on the Red Planet.