Misfit meteorites that don鈥檛 fit neatly into known categories could be relics from a lost Mercury-like world that was destroyed early in the history of the solar system.
Most asteroids that fall to Earth as meteorites can be grouped together and have common origins, with many derived from larger asteroids, the moon or Mars. But around 0.2 per cent of meteorites are outliers, resisting any neat categorisation.
Now, at the University of Minnesota and her colleagues think that one of these meteorites, found in north-west Africa in 2023 and called NWA 15915, has a geological signature suggesting it came from a Mercury-like world that no longer exists.
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When Mitchell and her team analysed the meteorite with an electron microscope and spectroscopic instruments, they found it had a composition distinct from that of Mercury, but that it nevertheless formed in a Mercury-like setting.
For instance, the minerals in the meteorite had formed in an environment with little oxygen 鈥� which is similar to the environment Mercury was born in.
NWA 15915 also had a unique mixture of metal-rich minerals with magnetic properties that suggested a Mercury-like origin, and the mineral crystals in the meteorite were relatively large, which indicates that the rock cooled slowly 鈥� again inviting similarities with Mercury.
鈥淭his is all suggestive of a large, differentiated body that might have been quite Mercury-like,鈥� Mitchell told the in The Woodlands, Texas, on 12 March.
Mitchell also presented a second misfit meteorite that she and her colleagues had been analysing, called Ksar Ghilane 022. It has similar characteristics, though different magnetic properties, that indicate it could also have come from a Mercury-like body. However, Mitchell emphasised that both of these investigations are at an early stage and it is difficult to make firm conclusions.
鈥淚f confirmed, it鈥檚 quite an exciting result,鈥� says at the Massachusetts Institute of Technology. There are some metal-rich asteroids in the solar system鈥檚 asteroid belt today whose formation we struggle to understand, which meteorites samples like these could also shed light on, he adds.
