Sahara Meteorite reveals evidence of lost Moon-sized planet

A one-pound rock pulled from the Sahara Desert in 2019 has just rewritten what scientists thought they knew about the early solar system, preserving what researchers describe as the first definitive evidence of a long-lost planet that may have been as large as Earth's moon before it was destroyed more than four billion years ago.

The meteorite, known as Northwest Africa 12774, falls into a class called angrites, among the rarest and oldest volcanic rocks recovered on Earth, with only 68 confirmed examples from more than 80,000 meteorites ever catalogued.

What makes NWA 12774 stand out even compared with other angrites is what geoscientist Aaron Bell and his colleagues at the University of Colorado Boulder discovered inside it: crystals of a mineral called clinopyroxene that turned out to be exceptionally rich in aluminium, a clue that points to crystallisation under extreme pressure.

The team’s analysis in the journal Earth and Planetary Science Letters reckoned those crystals needed pressures of at least 17.5 kilobars to grow at rates that were more than 17 times the pressure right at the bottom of the Mariana Trench. Notably, no small asteroid could conjure conditions like that in the first place.

They worked backward using the pressure info to figure out the smallest size the parent body must've had. The crystals' sharp edges and intact chemical patterns hint that these formed relatively shallow, since long exposure to a hot planet's insides would've smoothed them out. This detail bumps up the size estimate even more.