The fate of Earth during the Sun's giant phases: New constraints from ab initio tidal modelling and AGB mass loss

Abstract

The long-term evolution of planetary systems around solar-type stars is governed by the interplay between stellar expansion, tidal interactions, and mass loss during the red giant branch (RGB) and asymptotic giant branch (AGB) phases. However, tidal dissipation efficiencies and AGB mass-loss rates both remain poorly constrained, leading to significant uncertainty in predicting the fate of planetary systems, in particular, that of the Earth orbiting the ageing Sun. We reassess the survival of the Earth and the inner Solar System planets during the entire evolution of the Sun, focusing on the impact of updated tidal dissipation prescriptions and varying AGB mass-loss rates. We modelled the orbital evolution of the Earth using stellar evolution tracks for a solar-mass star. We compared these results with outcomes obtained using previously published and commonly adopted tidal prescriptions, and we explored a range of AGB mass-loss rates. We find that the predicted fate of the Earth is highly sensitive to the tidal model and the assumed mass-loss rate. Based on updated tidal dissipation prescriptions, Earth survives the RGB and AGB phases of the Sun. In contrast, the use of earlier tidal dissipation prescriptions leads to engulfment during the AGB phase. Furthermore, low AGB mass-loss rates result in engulfment, and vice versa. Using the observed mass-loss rates of the AGB star L2 Pup as a proxy for the Sun's future AGB mass-loss rate results in the survival of the Earth during the AGB phase when combined with our tidal dissipation evaluation. Given the current observational uncertainties in AGB mass-loss rates, the ultimate fate of the Earth remains uncertain, highlighting the need for improved constraints on the late-stages of stellar evolution. However, considering observational proxies for the Sun during the AGB phase, it is likely that the Earth will survive the Sun's giant phases.