Perseverance rover discovers igneous rocks interacting with water on Mars

The Surprise Discovery at the Margin Unit

When the Perseverance rover arrived at the inner edge of Jezero Crater in September 2023, mission scientists anticipated finding sedimentary rocks. Geological models based on orbital data of the area, dubbed the “Margin Unit,” suggested layers of sand, clay, and silt would line the ancient Martian lake shoreline. On Earth, these sedimentary layers excel at preserving signs of past microbial life.

Instead, the rover encountered igneous rocks formed deep underground from magma or through surface volcanic activity. Candice Bedford, a research scientist at Purdue University in West Lafayette, Indiana, and the study’s lead author, explained the shift in perspective. “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,” Bedford said. “But now we know that this location became a sort of crossroads for aqueous systems.”

SuperCam Laser Analysis Reveals Complex Water History

To uncover the geological history of the Margin Unit, scientists utilized Perseverance’s mast-mounted SuperCam instrument. The device determines mineralogy by analyzing the light reflected off geologic features. When researchers spotted compelling targets, they commanded SuperCam to fire a laser from up to 21 feet away, vaporizing tiny amounts of rock into plasma to reveal its chemical composition. The rover has targeted more than 185 bedrock sites using this method.

Through this detailed analysis, mineral crystals within the igneous rocks preserved an intricate timeline of water alteration. The data revealed that water interacted with the rocks on at least three distinct occasions, modifying their chemistry and appearance with each encounter. Eleni Ravanis, a planetary scientist at the University of Hawaii at Manoa and a coauthor of the study, noted that certain rocks within the unit also contain silica.

Elevation Differences Point to Olivine Alteration

Perseverance explored roughly 870 feet of elevation across the Margin Unit, revealing stark contrasts between higher and lower elevations. Higher up, the rover found coarse-grained, crystalline rocks rich in olivine with almost no indication of water exposure. Composed of magnesium and iron, this olivine unit cooled slowly deep underground in a body of magma and reached the surface only after overlying material eroded away.

Closer to the ancient lakebed lower in the unit, the rocks appeared heavily transformed. Olivine grains here were fractured, with silica filling the spaces between them. On Earth, reactions between water and olivine release hydrogen—a potential energy source for microbes—while leaving behind carbonate and silica. These specific minerals are critical signposts in the search for ancient life because they can lock in traces of past biological activity.

Frequently Asked Questions

What instruments did NASA use to study the Margin Unit?

The discoveries were made using Perseverance’s SuperCam, an instrument mounted on the rover’s mast that fires a laser at rocks and analyzes the resulting plasma to determine chemical makeup.

Why are carbonate and silica important in the search for Martian life?

When water interacts with olivine, it can produce hydrogen to feed microbes and leave behind carbonate and silica minerals, which are known for preserving traces of past microbial life.

Where are the Margin Unit findings published?

The study detailing these findings was published in the journal Communications Earth & Environment.