Jezero crater on Mars was chosen as the landing site for the Perseverance rover because satellite images suggested it was once an ancient lake. NASA scientists have now found more direct evidence of the location’s watery past, as photos snapped by the rover reveal signs of flash flooding.
While modern Mars is extremely dry, that wasn’t always the case – evidence is mounting that the Red Planet was much bluer billions of years ago, home to oceans, rivers, lakes, and possibly life. Finding evidence of this is a key goal for the Perseverance mission, and that’s why Jezero crater was selected.
Orbital images suggested that the 49-km (30 mile) wide crater was once a lake, fed by rivers from the northwest. As such, the northwestern rim of the crater appears to be a river delta, a fan-shaped deposit of sediment that built up in layers over many years. And in the new study, a rover’s-eye view of the structures has essentially confirmed these suspicions.
After Perseverance landed, it began snapping shots of its surroundings, including a series of steep escarpments (or scarps) about 2.2 km (1.2 miles) to the northwest, and a small butte nicknamed Kodiak to the southwest. Using its Mastcam-Z and Remote Micro-Imager (RMI) instruments, the rover was able to image the layers of rock and sediment in the formations.
And sure enough, those rocks tell a watery story. The layers of sediments in the eastern face of Kodiak, as well as the lower sections of the northwestern scarps, match what would be expected for a river delta here on Earth.
“Never before has such well-preserved stratigraphy been visible on Mars,” says Nicolas Mangold, lead author of the study. “This is the key observation that enables us to once and for all confirm the presence of a lake and river delta at Jezero.”
Extra clues were spotted on the upper sections of the scarps. Much larger stones and boulders were scattered around up there, some up to 1.5 m (5 ft) wide, which suggested that floodwaters had transported them from outside the crater. The team estimated that these waters would have had to be traveling at speeds of between 6 and 30 km/h (3.7 and 18.6 mph).
Altogether, the evidence suggests that the lake that filled Jezero crater was fairly dynamic over its lifetime, with water levels rising and falling between times of flood and calm.
The team says that the new study will inform upcoming missions, including where Perseverance will travel to take samples. Ultimately, the goal is to return the samples to Earth, where more powerful instruments can search for signs of ancient life.
“The finest-grained material at the bottom of the delta probably contains our best bet for finding evidence of organics and biosignatures,” says Sanjeev Gupta, co-author of the study. “And the boulders at the top will enable us to sample old pieces of crustal rocks. Both are main objectives for sampling and caching rocks before Mars Sample Return.”
The research was published in the journal Science.