The effects of stellar winds on the magnetospheres and potential habitability of exoplanets ^⋆

¹ SUPA, School of Physics and Astronomy, University of St Andrews, North Haugh, KY16 9SS, St Andrews, UK
e-mail: wcvs@st-andrews.ac.uk
² Observatoire de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
³ Université de Toulouse, UPS-OMP, Institut de Recherche en Astrophysique et Planétologie, 31400 Toulouse, France
⁴ CNRS, Institut de Recherche en Astrophysique et Planétologie, 14 Avenue Édouard Belin, 31400 Toulouse, France
⁵ Computational Engineering and Science Research Centre, University of Southern Queensland, 4350 Toowoomba, Australia
⁶ Universität Göttingen, Institut für Astrophysik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁷ Departmento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, CEP:59072-970 Natal, RN, Brazil
⁸ Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA

Received: 2 June 2014
Accepted: 6 August 2014

Abstract

Context. The principle definition of habitability for exoplanets is whether they can sustain liquid water on their surfaces, i.e. that they orbit within the habitable zone. However, the planet’s magnetosphere should also be considered, since without it, an exoplanet’s atmosphere may be eroded away by stellar winds.

Aims. The aim of this paper is to investigate magnetospheric protection of a planet from the effects of stellar winds from solar-mass stars.

Methods. We study hypothetical Earth-like exoplanets orbiting in the host star’s habitable zone for a sample of 124 solar-mass stars. These are targets that have been observed by the Bcool Collaboration. Using two wind models, we calculate the magnetospheric extent of each exoplanet. These wind models are computationally inexpensive and allow the community to quickly estimate the magnetospheric size of magnetised Earth-analogues orbiting cool stars.

Results. Most of the simulated planets in our sample can maintain a magnetosphere of ~5 Earth radii or larger. This suggests that magnetised Earth analogues in the habitable zones of solar analogues are able to protect their atmospheres and is in contrast to planets around young active M dwarfs. In general, we find that Earth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintain at least a Paleoarchean Earth sized magnetosphere. Our results indicate that planets around 0.6–0.8 solar-mass stars on the low activity side of the Vaughan-Preston gap are the optimum observing targets for habitable Earth analogues.