Planetary scientists have analyzed images taken by the Mastcam-Z camera and the Remote Micro-Imager of the SuperCam instrument on NASA’s Perseverance rover — which landed in Jezero crater in February 2021 — in the three months after landing. The images show the geologic layers of an ancient river delta, which formed when Jezero crater was filled by a lake. Named Lake Jezero, the paleolake could have been up to 40 km (25 miles) wide and tens of meters deep.
Mars is currently cold and hyper-arid, and liquid water is not stable at its surface.
However, orbital and rover observations of features including valley networks, sediments and ancient lake beds indicate the Red Planet once had a warmer, wetter climate.
NASA’s Mars 2020 mission, whose main component is the Perseverance rover, is the first step in a planned multi-mission campaign to return Martian samples to Earth and examine them for potential biosignatures.
The 45-km (28-mile) diameter Jezero crater was selected as the landing site based on orbital images, which showed geomorphic expressions of two sedimentary fan structures (western and northern) at the edges of the crater.
These were inferred to be river delta deposits that formed in an ancient lake basin during the Late Noachian or Early Hesperian epochs on Mars, about 3.6 to 3.8 billion years ago.
The Perseverance rover landed at Jezero Crater on February 18 , 2021. About a month later, its Mastcam-Z cameras and Remote Micro-Imager zoomed in for a closer look at one of the crater’s most massive geologic features, the Delta Scarp.
The scarp contains the remnants of a river delta that formed where a 193-km (120-mile) long ancient river and a 34-km (21-mile) wide lake join.
The Perseverance team detected a prominent hill, which they called Kodiak, near the scarp and discovered it contained distinctive geological structures.
Within its cliff face, they observed meters of sloping rock beds sandwiched between horizontal layers that indicate rocky deposits from the ancient delta.
This confirms the presence of the delta that built into a lake in Jezero crater and suggests that there was steady water flow into the lake, which is consistent with a warm and humid Martian climate 3.7 billion years ago.
“These results have an impact on the strategy for the selection of rocks for sampling,” said Imperial College London’s Professor Sanjeev Gupta.
“The finest grained material at the bottom of the delta probably contains our best bet for finding evidence of organics and biosignatures, 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 the Mars Sample Return — a future mission to bring these samples back to Earth.”
The researchers also spotted large boulders embedded in the uppermost layers of the Delta Scarp, which must have been transported by high-energy floods.
“We saw distinct layers containing boulders up to 1.5 m (5 feet) across that we knew had no business being there,” said Dr. Nicolas Mangold, a researcher at the Laboratoire de Planétologie and Géodynamique.
“The most surprising thing that’s come out of these images is the potential opportunity to catch the time when this crater transitioned from an Earth-like habitable environment, to this desolate landscape wasteland we see now,” said MIT Professor Benjamin Weiss.
“These boulder beds may be records of this transition, and we haven’t seen this in other places on Mars.”
The scientists also identified layers of what appear to be fine-grained clay and mudstones — types of rock that could potentially preserve traces of ancient life, if it ever existed on Mars.
“A better understanding of Jezero crater’s delta is a key to understanding the change in hydrology for the area, and it could potentially provide valuable insights into why the entire planet dried out,” Professor Gupta said.
The findings were published in the journal Science.
N. Mangold et al. Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars. Science, published online October 7, 2021; doi: 10.1126/science.abl4051