NASA’s Perseverance rover has discovered that a single geological location on Mars experienced at least three distinct episodes of water activity over its history, altering underlying igneous rock and creating conditions favorable for preserving ancient biosignatures.
Water Activity Transformation in Jezero Crater
When Perseverance arrived at the Margin Unit hugging the inner rim of Jezero Crater in September 2023, scientists anticipated finding typical sedimentary lake deposits. Instead, the rover encountered coarse, crystalline igneous rock rich in olivine at higher elevations. Lower down, however, that rock is fractured and chemically transformed.
Using the mast-mounted SuperCam instrument to fire a laser at more than 185 bedrock targets, researchers reconstructed three separate alteration events. First, carbon-dioxide-rich groundwater moved through fractures to produce carbonate. Second, lower-pH water—potentially the ancient lake itself—remobilized some of that carbonate and deposited silica in newly opened pore spaces. Finally, younger fractures filled with calcium-sulfate and fluorite-bearing veins, pointing to late hydrothermal activity.
“Before we arrived at the Margin Unit, the main hypothesis—derived from orbital observations—was that the carbonate seen from orbit formed from interaction with the lake that existed in Jezero Crater. But now we know that this location became a sort of crossroads for aqueous systems,” Candice Bedford of Purdue University, the study’s lead author, stated.
Expanding Exploration on the Lac de Charme Plateau
Operating beyond the Jezero Crater rim for over five years, Perseverance recently arrived at the Lac de Charme plateau to investigate some of the oldest magmatic rocks encountered during the mission. Enhanced onboard computing power allows the rover to navigate the deep valleys and rugged ridges of this western terrain with increased precision.
The dark rock formations on the plateau originated from ancient lava flows or asteroid impacts, predating the river channels and lakes inside Jezero Crater. Atanasios Klidaras, a graduate student at Purdue University, explained that these rocks formed during a period of intense asteroid bombardment on early Mars, providing clues about the planet’s earliest history and the evolution of rocky planets.
While the exact timing of the three water-rock alteration events in the Margin Unit remains unknown, the repeated exposure to chemically diverse waters enhances the astrobiological interest of the samples. On Earth, water interacting with olivine can release hydrogen to fuel microbes while leaving behind carbonate and silica capable of trapping microscopic traces of past life.
