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 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 while 17% and 9% orbits become unbound in the simulations over the past and future 5 Gyr. The ratio of unstable clones increases with the simulation time scale and encounter rate. The dynamical history of Proxima is sensitive to the uncertainty of the astrometric data as well as the uncertainty of the model of stellar encounters. This provides some evidence for a capture scenario for the formation of the current triple system. We note that the spectroscopic evidence in the literature indicates a super-solar metallicity for alpha Centauri and a solar one for Proxima supporting different origins and thus the capture hypothesis. Nonetheless, further improvements in the available data and models will be necessary for a reliable assessment of the history of the alpha Centauri system and its impact on the habitability of Proxima b.
F. Feng and H. Jones
Wed, 13 Sep 17
Comments: 6 pages, 3 figures, submitted to MNRAS