Was Proxima captured by alpha Centauri A and B?

TL;DR

This study uses simulations to explore whether Proxima Centauri was captured by alpha Centauri A and B, suggesting a possible capture scenario based on orbital stability and metallicity differences.

Contribution

It provides the first detailed dynamical simulation-based analysis of the orbital history of Proxima Centauri in the alpha Centauri system, indicating potential capture origins.

Findings

74% of Proxima clones remain bound over 5 Gyr

More than 50% of clones become unstable if the system migrated outward

Metallicity differences suggest different origins for Proxima and alpha Centauri

Abstract

The nearest stellar system consists of the stars Proxima, alpha Centauri A and B and at least one planet Proxima b. The habitability of Proxima b and any other planets are likely to be significantly influenced by the orbital evolution of the system. To study the dynamical evolution of the system, we simulate the motions of Proxima and alpha Centauri A and B due to the perturbations from the Galactic tide and stellar encounters in a Monte Carlo fashion. From 100 clones, we find that 74% orbits of Proxima Centauri are bound to alpha Centauri A and B while 17% and 9% orbits become unbound in the simulations over the past and future 5 Gyr. If the system migrated outward in the Milky Way to its current location, more than 50% of clones could become unstable in backward simulations. The ratio of unstable clones increases with the simulation time scale and encounter rate. This provides some evidence for a capture scenario for the formation of the current triple system. Despite large uncertainties, the metallicity difference between Proxima and alpha Centauri A and B is also suggestive of their different origin. Nonetheless, further improvements in the available data and models will be necessary for a reliable assessment of the history of the Proxima-alpha Centauri system and its impact on the habitability of Proxima b.