Data collected by NASA’s Perseverance probe from the Margin Unit area on the inner rim of Jezero Crater have revealed that Martian rocks interacted with water on at least three separate occasions. Most importantly, the area, which was thought to contain sedimentary rocks formed along the shores of an ancient lake, instead consists of igneous rocks that preserved a complex chemical record of the planet’s water history.
The study’s findings were published in Communications Earth & Environment. The team relied on the SuperCam instrument mounted on the probe’s mast, which analyzes minerals through reflected light and uses a laser to examine rocks at distances of up to 21 feet, or 6.5 meters. In this way, Perseverance analyzed more than 185 rock targets in the area.
From Igneous Rocks to a Multistage Water Record
The presence of carbonates, detected by orbiting spacecraft, had strengthened the hypothesis that the area formed as a result of interaction between ancient Jezero Lake and sediments. However, field examination revealed igneous rocks, some of which formed deep inside Mars from magma and later emerged at the surface after the erosion of the layers that had covered them.
Across an elevation of approximately 870 feet, or 265 meters, the probe found clear differences between parts of the unit. In the higher areas, coarse-grained rocks rich in the mineral olivine appeared, with almost no traces of previous interaction with water. In the lower sections near the floor of the ancient lake, olivine grains had fractured and silica minerals appeared among them.
Three Water Interactions and What the Minerals Reveal
The sequence of chemical alterations indicates that water reached the rocks in three stages:
- In the first stage, carbon dioxide-rich groundwater interacted with olivine, forming carbonates that filled cracks in the rocks.
- In the second stage, the interaction may have been associated with the lake that once existed in the crater, with larger quantities of silica appearing in rocks that had been below the waterline.
- In the third stage, mineral veins formed in an eastern part of the unit. They reached approximately 10 inches, or 25 centimeters, in thickness and contained calcium sulfate and fluorite.
The discovery of fluorite is particularly significant because it usually forms when hot water circulates through volcanic rocks. This provides evidence that the area was later exposed to a hot groundwater event, distinct from interaction with the lake or cold groundwater.
Why Does This Discovery Matter?
Carbonates and silica are important indicators in the study of the habitability of ancient Mars. On Earth, the interaction of water with olivine can release hydrogen, which may represent an energy source for some microbial organisms, while the process also leaves behind minerals capable of preserving traces of previous environmental conditions. However, the study does not prove that life existed; it identifies multiple aquatic environments that may have been suitable for preserving signs of life or supporting it.
The findings show that orbital data alone were not sufficient to determine the origin of the carbonates in the Margin Unit. The team can also arrange the stages of water interaction in sequence, but it cannot yet determine their ages. Therefore, the area provides an important record of changing climate and habitable conditions without resolving the timing of those events or the nature of ancient life on Mars.
These findings serve Perseverance’s primary astrobiology objective, as the probe characterizes Mars’s geology and past climate and collects samples of Martian rocks and regolith for storage.