Meteorite fragments found in the Sahara turn out to be from the most mysterious planet in our solar system

Just as Meteorite NWA 16788 “the largest piece of Mars on Earth” heads to auction, researchers believe they might have discovered two other extremely rare meteorite fragments from a distant planet.

Northwest Africa 15915 is one of three fragments of space debris found near Aougrout, Algeria by Jaouad Chaoui in October 2022. The largest stone weighs just under 1.4 kilograms. The stones are a pale yellow color, partially coated with a black fusion crust.

The fragment is classified as an achondrite, with a geochemical of composition including both the pyroxene mineral augite and magnesium-rich mineral enstatite.

So where did these meteorite fragments comes from?

A recent study published in Icarus by Open University academic, Dr Ben Rider-Stokes investigated the spectral properties of two of the pyroxene-rich achondrite meteorites unearthed in the Sahara Desert:. Northwest Africa 15915 and Ksar Ghilane 022. The study shed some some evidence that the stones could have originated from the surface of Mercury, the closest planet to the Sun in our solar system at 56,974,146 miles distance from Earth.

Mercury’s surface composition

Very little is known about the chemical makeup of Mercury’s surface and its mineralogy. Data obtained from the MESSENGER missions between 2011 and 2015 inferred that the planet’s surface predominantly consists of plagioclase as well as pyroxene, olivine and to a lesser degree, quartz.

The Sahara Desert meteorites contain both olivine and pyroxene, but only only trace amounts of plagioclase.

“Mercury has always been a bit of a mystery due to its unique mineralogy inferred from space missions,” Dr Rider-Stokes explains. “While many attempts have been made to link a meteorite to the planet, no such meteorite has been confidently linked. The discovery of these two unique meteorites, with a mineralogy similar to that of the surface, was an exciting surprise. This prompted a more in-depth analysis of their chemistry and isotopic compositions.”

Dr Rider-Stokes’ team calculated the formation age of the samples to 4528 ± 10 million years - much older than Mercury’s oldest recognized surface units (predicted to be approximately 4000 million years).

Where is Mercury in the solar system?

Another factor that challenges the claim that the stones came from Mercury is the physical improbability, based on the planet’s position in the solar system, as Rider-Stokes points out.

“Mercury is a lot closer to the sun, so anything that’s ejected off Mercury also has to escape the sun’s gravity to get to us. It is dynamically possible, just a lot harder. No one has confidently identified a meteorite from Mercury as of yet".

So there is no conclusive evidence that can unequivocally link Northwest Africa 15915 and Ksar Ghilane 022 to Mercury. Until a space mission is able to physically visit Mercury and bring back samples, it will be extremely difficult to assess a meteorite-planet link. However, spatial resolution analysis of surface composition is advancing all the time, so perhaps in the not too distant future, we will be able to identify a parental source for the Sahara Desert meteorites.

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