Rocky bodies called protoplanets were thought to have formed slightly earlier in the inner solar system than those beyond the asteroid belt, but now a meteorite from the outer solar system is rewriting that view
By Matthew Sparkes
4 July 2025
The Northwest Africa 12264 meteorite is older than expected
Ben Hoefnagels
Tiny shavings from a single meteorite could completely overturn our understanding of how the solar system formed, after the space rock turned out to be older than expected.
Previous research suggests that small rocky bodies called protoplanets formed throughout the solar system, but those found beyond the asteroid belt between Mars and Jupiter came together a bit later than those further towards the centre – 4.563 billion years ago, compared with 4.566 billion years ago for the inner protoplanets. This difference was thought to be because the outer bodies had more water and ice, which slowed down the melting of an inner core.
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This gap of three or four million years, although relatively short in cosmological terms, was a commonly accepted part of our cosmological history, but now Ben Rider-Stokes at The Open University in Milton Keynes, UK, and his colleagues say it has to go.
Planet formation is thought to involve accretion, in which dust and gas are pulled together by gravity, and then differentiation, in which the accreted material warms up and melts, separating into a core, mantle and crust. These processes were thought to have occurred at slightly different times for the inner and outer protoplanets of the early solar system, explaining their different history, but now it seems this isn’t the case.
The team’s discovery hinges on a small meteorite called Northwest Africa 12264, which weighs around 50 grams and was purchased from a dealer in Morocco in 2018. The researchers were given permission by its owners to analyse tiny particles shaved from the object. They found that the ratio of chromium and oxygen, which varies in a predictable way throughout our solar system, proved that the meteorite originated in the outer part.