Jezero Crater was chosen as the target for NASA’s Perseverance for its impressive river delta. Seen from orbit, it already told a story of water flowing on the surface of ancient Mars. In the initial months of work from the rover, the picture is expanding: The river was deeper and faster moving than it was possible to estimate from orbit.
The delta being explored is marked by curving layers, evidence of past water flow. NASA’s Curiosity rover in Gale Crater found evidence of shallow streams carving such structures. The hundreds of images taken by Perseverance (and now combined in two mosaics) reveal coarse sediment grains and cobbles. This was no rivulet – this was a powerful river.
“Those indicate a high-energy river that’s truckin’ and carrying a lot of debris. The more powerful the flow of water, the more easily it’s able to move larger pieces of material,” Libby Ives, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory, said in a statement. “It’s been a delight to look at rocks on another planet and see processes that are so familiar.”
One of the mosaiced areas was nicknamed “Skrinkle Haven” and features many curved layers that were left behind by the river. The team is not sure if they were created by the banks of the river shifting over time or if there were sandbars, small islands of sediments formed as the river flowed. These structures are believed to have been much taller, but the force of the wind over billions of years has eroded them away.
“The wind has acted like a scalpel that has cut the tops off these deposits,” said Michael Lamb of Caltech, a river specialist and Perseverance science team collaborator. “We do see deposits like this on Earth, but they’re never as well exposed as they are here on Mars. Earth is covered in vegetation that hides these layers.”
The other area is known as Pinestand about 450 meters (1,476 feet) from Skrinkle Haven. Pinestand is an isolated hill with sedimentary deposits curving skyward. Some are as high as 20 meters (66 feet).
"These layers are anomalously tall for rivers on Earth,” Ives said. “But at the same time, the most common way to create these kinds of landforms would be a river.”
The team is investigating alternative explanations for the formation. After all, this is still early days in the investigation of the delta. More observations will deliver more insights into the past of Mars including its potential habitability.
“What’s exciting here is we’ve entered a new phase of Jezero’s history. And it’s the first time we’re seeing environments like this on Mars,” added Perseverance’s deputy project scientist, Katie Stack Morgan of JPL. “We’re thinking about rivers on a different scale than we have before.”