The Sun's Birth Environment: Context for Meteoritics

TL;DR

This paper reviews the Sun's birth environment, analyzing meteoritic data and astrophysical evidence to infer the conditions and stellar neighborhood where the Sun formed, impacting planet formation and radionuclide acquisition.

Contribution

It provides a comprehensive synthesis of meteoritic and astrophysical data to constrain the Sun's birth environment and its implications for early solar system evolution.

Findings

The Sun likely formed in a bound stellar cluster similar to Orion's outskirts.

The protoplanetary disk was exposed to UV flux G0 ~30-3000 during formation.

Radionuclides like 26Al were inherited from the molecular cloud, influenced by supernovae and stellar winds.

Abstract

Meteorites trace planet formation in the Sun's protoplanetary disk, but they also record the influence of the Sun's birth environment. Whether the Sun formed in a region like Taurus-Auriga with ~10^2 stars, or a region like the Carina Nebula with ~10^6 stars, matters for how large the Sun's disk was, for how long and from how far away it accreted gas from the molecular cloud, and how it acquired radionuclides like 26Al. To provide context for the interpretation of meteoritic data, we review what is known about the Sun's birth environment. Based on an inferred gas disk outer radius ~50-90 AU, radial transport in the disk, and the abundances of noble gases in Jupiter's atmosphere, the Sun's molecular cloud and protoplanetary disk were exposed to an ultraviolet flux G0 ~30-3000 during its birth and first ~10 Myr of evolution. Based on the orbits of Kuiper Belt objects, the Solar System was subsequently exposed to a stellar density ~100 Msol/pc^3 for ~100 Myr, strongly implying formation in a bound cluster. These facts suggest formation in a region like the outskirts of the Orion Nebula, perhaps 2 pc from the center. The protoplanetary disk might have accreted gas for many Myr, but a few x10^5 yr seems more likely. It probably inherited radionuclides from its molecular cloud, enriched by inputs from supernovae and especially Wolf-Rayet star winds, and acquired a typical amount of 26Al.