Perseverance Rover finds ancient Martian beach with evidence of waves

A new paper reports that parts of Jezero crater's Margin Unit include a beach-like Eastern Margin Unit with cross-stratified, rounded grains consistent with wave action, while the Western Margin Unit shows igneous alteration; samples mentioned in the study remain on Mars after the Mars Sample Return program was cancelled.

When Perseverance landed in Jezero crater in 2021, orbital images already suggested a ring of unusual rocks. A new paper by Alex Jones (Imperial College London) and co-authors examines that Margin Unit and separates it into two subunits. The study reports that one subunit shows igneous alteration while the other has features consistent with a shoreline and wave action. The paper also notes a sampled rock called Comet Geyser and places the results in the context of sample-return plans. Key findings: - The Margin Unit is split into a Western Margin Unit (WMU) and an Eastern Margin Unit (EMU). - The WMU lies near the crater rim and is described as largely structureless igneous rock with olivine altered to carbonates and silica, likely by carbon-dioxide rich fluids. - The WMU alteration could be linked to hydrothermal activity, a process of interest for astrobiology. - The EMU shows cross-stratification, eroded surfaces, and rounded sandstone grains consistent with deposition and wave action in a shore zone. - Wave-formed sediments imply surface liquid water that was not frozen at the time and a thicker ancient atmosphere capable of generating wind-driven waves. - The study notes the sample called Comet Geyser as having high potential for preserved signs of ancient life, and it reports that Mars Sample Return was recently cancelled, leaving those samples on Mars. Summary: The paper strengthens evidence that Jezero crater once hosted a high-energy lacustrine shore, with one margin altered by igneous and fluid processes and the other showing beach-like sedimentary features. Those conditions are relevant to astrobiology because carbonates and silica can preserve microscopic fossils. Mars Sample Return was cancelled and the fate of the collected samples is undetermined at this time.