4.5-billion-year-old meteorites found in North Africa could be first pieces of Mercury on Earth

Meteorites originating from Mars have been discovered on Earth in the past, but none from Mercury. This intrigued planetary scientist Ben Rider-Stokes of The Open University in the UK. His study shows that meteorites discovered in the Sahara desert might have come from Mercury as suspected, even though their composition did not match the description of the first planet of the solar system. So, how did he know? Mercury is only about 58 million km from the Sun, with a temperature of 167 degrees Celsius. It is a hot mess of iron and silicates. After the solar system formed, asteroids continued to bombard planets, releasing a ton of debris that littered other cosmic bodies. So something from Mercury was bound to be present on Earth.

Meteorites found in Tunisia and Morocco

Landing a rover is almost impossible on Mercury. The MESSENGER spacecraft that orbited Mercury learned about the composition of the planet. Stokes took the meteorite samples that were suspected of being from Mercury, but there was no confirmation. These meteorites were Ksar Ghilane 022, which was found in Tunisia, and Northwest Africa 15915, discovered in Morocco. The signs were promising. Their surface composition and mineralogy were similar to Mercury's crust. They are both achondrites that do not match previously known achondrites. They comprise silicates such as olivine and pyroxene, often found in igneous and metamorphic rocks, apart from plagioclase and oldhamite. However, the iron-free silicates and oxygen isotopes they have are similar to aubrites, a substance not found on Mercury. So these meteorites couldn't possibly be from Mercury.

Pieces of ancient Mercury?

Except, they could be. “It is not believed that the aubrites originated from Mercury, as the planet has an extremely red spectrum which differs from aubrite spectra, but it has been suggested that aubrites represent a proto-Mercury,” said Stokes. However, when the solar system was still in its infancy billions of years ago, Mercury could have had a different composition. The meteorites are dated to be 4.5 billion years old, way older than other material zooming through the solar system. Mercury today is smooth, and this happened only around 3.6 billion years ago. So the meteorites still could be from Mercury, possibly remnants of an ancient planet, when collisions had not exposed the material under it. BepiColombo, a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA), is on its way to Mercury and is expected to arrive in early 2026. Stokes thinks that this spacecraft could possibly find a source for the material found in these mysterious rocks.