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

摘要

Context: The principle definition of habitability for exoplanets is whetherthey can sustain liquid water on their surfaces, i.e. that they orbit withinthe habitable zone. However, the planet's magnetosphere should also beconsidered, since without it, an exoplanet's atmosphere may be eroded away bystellar winds. Aims: The aim of this paper is to investigate magnetosphericprotection of a planet from the effects of stellar winds from solar-mass stars.Methods: We study hypothetical Earth-like exoplanets orbiting in the hoststar's habitable zone for a sample of 124 solar-mass stars. These are targetsthat have been observed by the Bcool collaboration. Using two wind models, wecalculate the magnetospheric extent of each exoplanet. These wind models arecomputationally inexpensive and allow the community to quickly estimate themagnetospheric size of magnetised Earth-analogues orbiting cool stars. Results:Most of the simulated planets in our sample can maintain a magnetosphere of ~5Earth radii or larger. This suggests that magnetised Earth analogues in thehabitable zones of solar analogues are able to protect their atmospheres and isin contrast to planets around young active M dwarfs. In general, we find thatEarth-analogues around solar-type stars, of age 1.5 Gyr or older, can maintainat least a Paleoarchean Earth sized magnetosphere. Our results indicate thatplanets around 0.6 - 0.8 solar-mass stars on the low activity side of theVaughan-Preston gap are the optimum observing targets for habitable Earthanalogues.