Quantifying the high early solar cosmic ray flux with cosmogenic neon isotopes in refractory minerals

TL;DR

This study estimates that the early solar cosmic ray flux was up to 10^7 times higher than today, using cosmogenic neon isotopes in ancient refractory minerals, aligning with astronomical observations of young stellar objects.

Contribution

It provides the first quantitative constraint on the magnitude of the early solar cosmic-ray flux using in situ cosmogenic neon in primitive minerals.

Findings

Early SCR flux was up to ~10^7 times higher than current levels.

Effective exposure time to SCRs was on the order of years.

Results align with astronomical observations of young stellar objects' flare activity.

Abstract

An enhancement in the activity of the early young Sun resulting in a high charged particle flux has been invoked to explain excesses in spallation-induced nuclides in primitive planetary materials. Astronomical observations of energetic outbursts of young stellar objects (YSOs) also support the idea of an active young Sun. However, the early solar cosmic-ray (SCR) flux has not been well constrained. Here we use measured concentrations of SCR-produced nuclides that formed and are preserved in meteoritical hibonite and spinel, some of the oldest solids formed in the Solar System, and physical models for dust transport in the early protoplanetary disk to determine the magnitude of the early SCR flux. We focus our attention on cosmogenic neon which cannot have been inherited from precursors and can only be produced in situ in solids. Our modeled effective exposure time to SCRs for these solids is very short on the order of years. This indicates the early SCR flux recorded in refractory mineral hibonite was up to ~7 orders of magnitude higher than the contemporary level. Our flux estimate is consistent with the >10^5 enhanced flux inferred from astronomical observations of greatly enhanced flare activities of YSOs.