LAUSR

Cosmic Dust Some primitive meteorites contain presolar grains, which are solid particles that formed in the interstellar medium before being incorporated into the Solar System. Presolar grains were known to be older than the Sun but had not been precisely dated. Heck et al. examined neon isotopes in presolar silicon carbide grains extracted from the Murchison CM2 meteorite. This allowed them to calculate how long each grain had remained in the interstellar medium, a period of time ranging from 3.9 ± 1.6 million years up to 3 ± 2 billion years before the formation of the Solar System, making the grains the oldest known solid material. Most grains had presolar ages of less than 300 million years, constraining astronomers' models of how long dust survives in the interstellar medium. Proc. Natl. Acad. Sci. U.S.A. 117 , 1884 (2020).