The Range of Cumulative XUV Flux on GJ 1132 b

TL;DR

This study models the XUV radiation history of GJ 1132 and its impact on GJ 1132 b, revealing the planet likely received intense XUV flux leading to atmospheric loss, with flares contributing significantly.

Contribution

It compares different XUV evolution models, incorporates flare data, and assesses the planet's atmospheric erosion risk with a focus on empirical versus solar twin models.

Findings

GJ 1132 is likely many Gyr old with few observed flares.

GJ 1132 b received over 50 times Earth's XUV flux, risking atmospheric loss.

Empirical XUV models predict 2-3 times more flux than solar twin models.

Abstract

We investigate the plausible history of the XUV luminosity evolution of the planet-hosting M4 star GJ 1132 (~0.2 solar masses) to infer the cumulative incident XUV flux intercepted by the short-period (~1.6 d) Earth-sized transiting planet GJ 1132 b. We include the dominant observational uncertainties, compare two quiescent XUV luminosity evolution models, and simulate the XUV luminosity evolution from flares based on TESS data and a re-analysis of Kepler stars. We find only 4 flares in GJ 1132's TESS 123 day lightcurve, which is relatively few for M dwarfs and, in conjunction with the ~125 day period, suggests that this star is many Gyr old. We find that all model permutations predict that the planet has at least a 95% chance of receiving more than 50 times as much XUV flux as modern Earth, confirming that this planet is a good candidate for permanent atmospheric loss. We also find that an empirical XUV model for M dwarfs predicts 2-3 times more total XUV flux than a commonly used solar twin model and that the empirical model's distribution is 2-3 times narrower. Flares contribute about 20% of the cumulative XUV flux on planet b, which, while modest, ensures the planet lies firmly on the atmosphere-free side of the "cosmic shoreline."