Isotopic enrichment of planetary systems from Asymptotic Giant Branch stars

TL;DR

This paper explores how evolved Asymptotic Giant Branch stars can enrich planetary systems with short-lived radioisotopes like 26-Al and 60-Fe, potentially influencing planetary heating, supported by Gaia data discovery and simulation results.

Contribution

It demonstrates that encounters between AGB stars and young planetary systems are plausible and can deliver isotopes consistent with Solar System observations.

Findings

AGB stars can produce sufficient 26-Al and 60-Fe yields.

Encounters between AGB stars and star-forming regions are possible.

AGB enrichment can account for observed isotope levels in the Solar System.

Abstract

Short-lived radioisotopes, in particular 26-Al and 60-Fe, are thought to contribute to the internal heating of the Earth, but are significantly more abundant in the Solar System compared to the Interstellar Medium. The presence of their decay products in the oldest Solar System objects argues for their inclusion in the Sun's protoplanetary disc almost immediately after the star formation event that formed the Sun. Various scenarios have been proposed for their delivery to the Solar System, usually involving one or more core-collapse supernovae of massive stars. An alternative scenario involves the young Sun encountering an evolved Asymptotic Giant Branch (AGB) star. AGBs were previously discounted as a viable enrichment scenario for the Solar System due to the presumed low probability of an encounter between an old, evolved star and a young pre-main sequence star. We report the discovery in Gaia data of an interloping AGB star in the star-forming region NGC2264, demonstrating that old, evolved stars can encounter young forming planetary systems. We use simulations to calculate the yields of 26-Al and 60-Fe from AGBs and their contribution to the long-term geophysical heating of a planet, and find that these are comfortably within the range previously calculated for the Solar System.