mages taken by the Perseverance rover in Mars’ Jezero crater show the geologic layers of an ancient river delta, which formed when the crater was filled by a lake, according to a new analysis. The study shows how much water flowed into this crater about 3.7 billion years ago, and indicates where the rover could search for biosignatures or organic material. The Perseverance rover landed in Jezero in February 2021. 

Nicolas Mangold and Sanjeev Gupta et al. analyze images taken by the rover of cliff faces at the edge of the delta. By measuring the dip of rock layers within the cliffs and the shapes and sizes of the boulders contained within them, the researchers conclude that the delta advanced into an ancient lake that varied in depth over time. The analysis shows there was a steady flow into the lake at first, consistent with a warm and humid Martian climate 3.7 billion years ago. 

There are large boulders embedded in the upper (more recent) cliff layers, which must have been transported by high-energy floods. At the bottom of the cliffs, the authors identify promising 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.