Early Solar System irradiation quantified by linked vanadium and beryllium isotope variations in meteorites

TL;DR

This study uses vanadium and beryllium isotope variations in meteorites to quantify early Solar System irradiation, revealing that refractory dust was irradiated by solar cosmic rays from gradual flares for less than 300 years near the protoSun.

Contribution

It provides the first direct isotopic evidence linking vanadium and beryllium variations to early Solar System irradiation conditions, specifically from gradual solar flares.

Findings

50V excesses up to 4.4 per mil in CAIs co-vary with 10Be abundance

Refractory dust was irradiated by solar cosmic rays for less than 300 years

Irradiation occurred at about 0.1 au from the protoSun

Abstract

X-ray emission in young stellar objects (YSOs) is orders of magnitude more intense than in main sequence stars1,2, suggestive of cosmic ray irradiation of surrounding accretion disks. Protoplanetary disk irradiation has been detected around YSOs by HERSCHEL3. In our solar system, short-lived 10Be (half-life = 1.39 My4), which cannot be produced by stellar nucleosynthesis, was discovered in the oldest solar system solids, the calcium-aluminium-rich inclusions (CAIs)5. The high 10Be abundance, as well as detection of other irradiation tracers6,7, suggest 10Be likely originates from cosmic ray irradiation caused by solar flares8. Nevertheless, the nature of these flares (gradual or impulsive), the target (gas or dust), and the duration and location of irradiation remain unknown. Here we use the vanadium isotopic composition, together with initial 10Be abundance to quantify irradiation conditions in the early Solar System9. For the initial 10Be abundances recorded in CAIs, 50V excesses of a few per mil relative to chondrites have been predicted10,11. We report 50V excesses in CAIs up to 4.4 per mil that co-vary with 10Be abundance. Their co-variation dictates that excess 50V and 10Be were synthesised through irradiation of refractory dust. Modelling of the production rate of 50V and 10Be demonstrates that the dust was exposed to solar cosmic rays produced by gradual flares for less than 300 years at about 0.1 au from the protoSun.