Perseverance has uncovered a 75-metre-thick stack of ancient rock on the rim of Jezero crater. Dubbed the "Broom Point member," it may be the oldest rock record any rover has ever examined on another planet.
Rovers do not usually climb to the top of a crater to read a history book. Yet that is exactly where NASA's Perseverance has been driving on Mars. On the rim of Jezero crater, the robot is rolling through a band of bright-coloured rocks that scientists have nicknamed the Broom Point member. Initial analysis suggests this 75-metre-thick stack of layered bedrock is older than 3.9 billion years — older than almost any surface terrain a rover has ever reached.
The working picture that emerged from the rover's data is one of a young Mars being hammered from above. The rock sequence on the rim appears to have been built not by slow sedimentation at the bottom of a lake, but by a series of repeated asteroid impacts that piled debris layer upon layer. Each impact laid down a new sheet of material, and over eons those sheets accumulated into the thick, striated cliffside Perseverance now has its cameras pressed against.
Jezero was a lake in Mars's distant past, and Perseverance spent years sampling its ancient shorelines and river delta in search of traces of life. But the rim holds a different kind of record. While the lake sediments tell the story of one valley at one moment, the rim's impact debris archives billions of years of violence across the whole early Solar System. Reading it is like swapping a single diary page for the full chronicle.
Perseverance's original mission was to find signs of ancient habitability at the lake. The rim findings do not displace that goal; they deepen it. If the earliest rocks on Mars preserve the chemistry and physics of that bombardment era, then the conditions under which any future life might have arisen can be dated with far greater precision. The rover's next targets are not just rocks — they are chapters of a 3.9-billion-year-old diary.