NASA’s Perseverance Rover Uncovers Ancient Impact Record on Mars

NASA’s Perseverance rover has identified a 75-metre-thick sequence of ancient rock on the rim of Jezero Crater, known as the “Broom Point member”, formed by repeated asteroid impacts over 3.9 billion years ago. Published in the Journal of Geophysical Research: Planets, the findings reveal six distinct rock types, including breccias and glassy beads indicative of high-energy impacts rather than volcanic activity. The layered structure suggests a “one-two punch” of cosmic events: first, the formation of the Isidis Basin tilted the rock layers, followed by the impact that created Jezero Crater. Core samples collected by the rover may help date these events, offering insights into the early solar system’s bombardment history.

The Broom Point member is likely more than 3.9 billion years old, making it among the oldest terrain examined by a Mars rover. Rock fragments within the breccias are pocked with gas-bubble cavities, indicating they were once molten. Tiny, dark, glassy beads found in the layers rival those flung out by the dinosaur-killing Chicxulub asteroid’s impact on Earth. Several layers appear to be formed by fast, ground-hugging debris flows, possibly caused by molten rock hitting water or ice.

Some layers tilt at angles exceeding 80 degrees, which is too steep to be caused by the Jezero Crater impact alone. The Perseverance team has collected two core samples, dubbed “Bell Island” and “Main River”, for potential future return to Earth for laboratory dating. Ken Farley, Perseverance deputy project scientist, noted that Mars lacks plate tectonics, preserving this ancient record unlike on Earth. Alex Jones, lead author of the paper, stated that the layers record variable-sized impacts occurring at different distances from the accumulation site.

The study provides a window into one of the most tumultuous chapters in the history of the solar system. While volcanoes can produce similar glassy droplets, they rarely occur in such high abundance, pointing to asteroid impacts as the primary architect. The repetition of distinct rock types throughout the thick sequence indicates that high-energy impact events happened again and again across this region of early Mars.

Scientists suspect a cosmic “one-two punch” shaped this landscape long ago. First, a colossal asteroid impact created the 1,200-mile-wide Isidis Basin, upending and tilting the once-flat rock layers. Later, a second asteroid likely struck, forming Jezero Crater, which fractured and uplifted the already-tilted rocks into the dramatic formations the rover sees today.

If a future mission were to return the core samples to Earth, laboratory dating could determine when and how often impacts were occurring on early Mars. This data would also shed light on the infant Earth, whose own early impact record has been erased by billions of years of plate tectonics. During this violent era, the sky was filled with an almost constant barrage of molten rock droplets and pulverised dust kicked up by asteroid impacts.

The findings highlight the unique value of Mars as a geological archive. Because the planet lacks plate tectonics to recycle its crust, this ancient record remains intact. This preservation gives scientists a rare glimpse into a geological time period that does not exist on our own planet, offering critical context for understanding the early solar system’s bombardment history.