Magnetic Fields on the Flare Star Trappist-1: Consequences for Radius Inflation and Planetary Habitability

Abstract

We construct evolutionary models of Trappist-1 in which magnetic fields impede the onset of convection according to a physics-based criterion. In the models that best fit all observational constraints, the photospheric fields in Tr-1 are found to be in the range 1450–1700 G. These are weaker by a factor of about 2 than the fields we obtained in previous magnetic models of two other cool dwarfs (GJ 65A/B). Our results suggest that Tr-1 possesses a global poloidal field that is ∼100 times stronger than the Sun’s global field. In the context of exoplanets in orbit around Tr-1, the strong poloidal fields on the star may help to protect the planets from the potentially destructive effects of coronal mass ejections. This, in combination with previous arguments about the beneficial effects of flare photons in the ultraviolet and visible portions of the spectrum, suggests that conditions on Tr-1 are not necessarily harmful to life on a planet in the habitable zone of Tr-1.