NASA’s Perseverance has been trundling around Mars for more than seven months and it has already delivered some important science. Now, the first results from the mission have been published and it confirms the nature of the region the rover was sent to explore. Jezero crater, the site of Perseverance's touchdown, was indeed an ancient Martian lake 3.6 billion years ago.

Evidence of deltas from satellite observations had suggested that but observations from the rover's first three months have confirmed it. Published in the journal Science, observations from Perseverance reveal sediment arrangements known as "scarps" that suggest the flow of the deltas turned into a lake, and reveals episodes of dramatic flooding shifted the massive boulders found in the crater.

“If you look at these images, you’re basically staring at this epic desert landscape. It’s the most forlorn place you could ever visit,” co-author professor Benjamin Weiss, from MIT, said in a statement. “There’s not a drop of water anywhere, and yet, here we have evidence of a very different past. Something very profound happened in the planet’s history.”

Composite image of the “Delta Scarp” in Jezero Crater. The inset zooms in on a 115-meter-wide portion of the scarp, allowing closer inspection of the boulder containing flood deposits at the top of the Delta Scarp. Image credit: NASA/JPL-Caltech/LANL/CNES/CNRS/IRAP/LPG/ASU/MSSS

When Mars, and Jezero crater in particular, was wet, it was a very different world. A world that might have even hosted life. Perseverance has been collecting samples from Jezero crater that will in a few years be sent back to Earth to help us determine whether Mars did, or could, host life. The entire location is a time capsule of what the Red Planet was like, so is the perfect place to look.

Orbital view of the delta fan in Jezero crater from the HiRISE camera onboard NASA’s Mars Reconnaissance Orbiter. Image credit: NASA/JPL-Caltech/University of Arizona

“The mission's goal is to use the rover to help us understand the geology and ancient climate of Mars, and to try to detect traces of past life which might still be preserved," lead author Nicolas Mangold, CNRS senior researcher at Laboratoire Planétologie et Géodynamique, said in a statement. "To do this, Perseverance has to sample rocks of various types and ages."

Even though signs from orbital satellites seemed obvious, the Spirit rover never was able to confirm that Gusev Crater was an ancient Martian lake, so this is exciting data from Perseverance. The rover's observations suggest the lake was probably lower than previous estimates. The large boulders on top of the fluvial deposit suggest that the river delta occasionally experienced dramatic fast flows that flooded the crater and carried the boulders from further afield into it.

What the lake may have looked like. The red star indicates Octavia E. Butler (OEB) landing site of the Perseverance rover. Image credit: NASA/JPL-Caltech/MSSS/LPG

“This observation strongly suggests that there was an abrupt hydrological change, linked to a climate transition that heralded the disappearance of the lake," Mangold added. "This could be explained by cooling due to a glacier or to increasingly arid conditions. In fact, on Earth, certain deserts undergo episodes of flash floods which appear and disappear in just a few hours."

The rover will continue moving across the landscape of the former delta, and the team hopes to investigate those large boulders to better understand what happened to them. This is not the first recent mention of violent flooding on Mars, suggesting an ancient world with a lot more dramatic dynamism.