Meteorite NWA 7831 – Western Sahara

Meteorite NWA 7831 is a fascinating specimen of diogenite, a type of achondrite that comes from the mantle of the asteroid Vesta. This meteorite was discovered in March 2013 in the Western Sahara, specifically in the Saguia el Hamra region. The total mass of all the pieces found is approximately 20 kilograms.

Diogenites, which include NWA 7831, are deep-seated igneous rocks that formed deep beneath the surface of Vesta, one of the largest objects in the main asteroid belt between Mars and Jupiter. Vesta is considered a protoplanet with a differentiated planetary structure, meaning it has a core, mantle and crust. This differentiation is similar to what we find in terrestrial planets. Diogenites contain high amounts of pyroxene, a mineral rich in iron and magnesium, and often smaller amounts of olivine and plagioclase.

NWA 7831 is notable for its composition, which includes mainly yellow-green orthopyroxene crystals. This type of mineral is relatively rare in meteorites and its presence indicates specific conditions of crystallization and formation deep within the mantle of Vesta.

The Dawn spacecraft, which studied the asteroid Vesta in 2011 and 2012, provided important data that were crucial for comparing terrestrial finds such as NWA 7831 with Vesta's surface and subsurface structures, allowing scientists to confirm that certain types of meteorites, including diogenites, originated on this asteroid. The results provided evidence that diogenites were ejected from Vesta during collisions with other asteroids and subsequently impacted Earth as meteorites.