NASA’s Perseverance Mars rover has discovered evidence that a 245-foot (75-meter-thick) pile of ancient rock on the rim of Jezero Crater was built by repeated asteroid impacts. This sequence of layered bedrock, dubbed the “Broom Point Member” by the rover’s science team, is likely more than 3.9 billion years old, making it some of the oldest terrain ever examined by a Mars rover.

Published Wednesday in the Journal of Geophysical Research: Planets, the findings offer a window into one of the most tumultuous chapters in the history of the solar system.

“Since leaving Jezero, Perseverance has been exploring a new frontier, both geographically and geologically: a chapter of Martian time before the crater itself,” said Ken Farley, Perseverance deputy project scientist at Caltech in Pasadena, California. “On Earth, our earliest geological history has been fundamentally broken, warped and erased by plate tectonics. Because Mars lacks plate tectonics to recycle its crust, this ancient record remains intact, giving us a rare glimpse into a geological time period that does not exist on our own planet.”

After ascending the western rim of Jezero Crater in late 2024, Perseverance began surveying the surrounding locations with its scientific instruments. Their data at Broom Point revealed six distinct rock types, including breccia (rocks composed of angular fragments) alternating with layers of fine-grained, pulverized rock dust. The rock fragments within the breccias are filled with cavities of gas bubbles, indicating that they were once molten.

The presence of small, dark glassy beads within the layers offered an important clue as to how these rocks were formed. While volcanoes can produce similar glassy blobs, they rarely occur in such abundance, pointing to asteroid impacts as the primary architect. In fact, the largest beads rival those thrown up by the Chicxulub asteroid impact that killed the dinosaurs on Earth.

The repetition of these different rock types several times throughout this thick rock sequence indicates that high-energy impact events occurred again and again in this region of early Mars.

“The different rock layers are a record of impacts of variable size that occur at different distances from where this sequence of rocks accumulated,” said Alex Jones, Ph.D. student of planetary geology at Imperial College London and lead author of the paper. “Some big impacts took place very far away, some small impacts close by. All of their debris ended up landing here, building up this thick section of rock.”

The way these layers formed may suggest an interaction with water or ice. Several of the layers appear to have been formed by rapid debris flows approaching the ground. On Earth, these powerful fluid-like surges can occur when molten rock collides with water or ice that instantly turns into vapor.

Some of Broom Point’s layers tilt at angles greater than 80 degrees (nearly vertical), which is too steep to be caused by the impact that created Jezero Crater.

Instead, scientists suspect that a cosmic “double whammy” shaped this landscape long ago. First, the colossal asteroid impact created the 1,900-kilometer-wide (1,200-mile) Isidis Basin, one of the largest impact basins on Mars, upending and tilting once-flat rock layers. Later, a second asteroid likely impacted, forming Jezero Crater, which measures 45 kilometers (28 miles) wide. This second impact fractured and uplifted the already tilted rocks to form the spectacular formations that the rover sees today.

To pinpoint exactly when these events took place, the Perseverance team collected two core samples, named “Bell Island” and “Main River.” If a future mission were to return them to Earth, laboratory dating could determine when and how often impacts occurred on early Mars and, by extension, infant Earth, whose own record of early impacts has been erased by billions of years of plate tectonics.

“During this violent era, it wasn’t rain or snow falling from the sky, but rather a near-constant barrage of droplets of molten rock and pulverized dust kicked up by asteroid impacts,” Jones said. “If we could pinpoint the age of these layers, it would be like reading a cosmic weather report from 4 billion years ago.”

NASA’s Jet Propulsion Laboratory in Southern California, managed by Caltech for the agency, built and manages operations of the Perseverance rover on behalf of the agency’s Science Mission Directorate in Washington, as part of NASA’s Mars Exploration Program portfolio. Arizona State University leads operations of the rover’s Mastcam-Z instrument, working in collaboration with Malin Space Science Systems in San Diego, on the design, manufacturing, testing and operation of the cameras. SuperCam is led by Los Alamos National Laboratory in New Mexico, where the instrument’s Body Unit was developed. The rover’s SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) instrument was built at NASA JPL, and its WATSON (Wide-Angle Topographic Sensor for Operations and Engineering) camera was built at Malin Space Science Systems.

For more information about NASA’s Perseverance, visit:

https://science.nasa.gov/mission/mars-2020-perseverance

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