Perseverance Rover Finds 3.9-Billion-Year-Old Impact Layer on Jezero Rim, Illuminating Late Heavy Bombardment

The Perseverance rover has uncovered a massive, 75‑meter‑thick stack of layered rock on the western rim of Jezero Crater. This formation, dubbed the “Broom Point member,” dates to roughly 3.9 billion years ago, placing it squarely in the Solar System’s Late Heavy Bombardment. Because Mars lacks plate tectonics, the record remains largely intact, offering a rare glimpse of a time that Earth’s surface no longer preserves. The discovery reshapes our understanding of early planetary impacts across the inner Solar System.

What happened

Perseverance moved from the floor of Jezero to its western rim in late 2024 and began surveying a newly exposed outcrop. Using its suite of spectrometers and cameras, the rover identified a 75‑meter‑thick sequence of alternating breccias and fine‑grained dust, which the science team named the Broom Point member. Laboratory analysis of the spectral data indicates the rocks formed around 3.9 billion years ago, making them among the oldest surfaces ever examined by a rover.

The outcrop contains six distinct rock types arranged in tight layers, each bounded by angular fragments that point to repeated high‑energy impacts. The presence of breccias—rock fragments cemented together—suggests that the material was shattered and re‑deposited by successive asteroid collisions during the Late Heavy Bombardment period (4.1–3.8 billion years ago).

Why it matters

The Broom Point member provides a tangible record of the Late Heavy Bombardment, a chaotic era that reshaped the inner planets and may have influenced the emergence of life on Earth. Because Mars has preserved its crust, this layer offers a calibration point for crater‑count dating methods used across the Solar System. Understanding the intensity and timing of early impacts helps refine models of planetary formation and the delivery of water and organics to early Earth.

How to think about it

Treat the Broom Point member as a case study in planetary stratigraphy: a preserved impact‑laden sequence that can be compared with lunar highland samples and meteorite ages. When evaluating its significance, weigh the robustness of the spectral dating against the limitation of a single outcrop, and consider how future missions—especially sample‑return—could confirm or refine these findings.

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