Rotational Synchronization May Enhance Habitability for Circumbinary Planets: Kepler Binary Case Studies

TL;DR

This paper explores how tidal synchronization in binary star systems can reduce stellar activity, potentially increasing the habitability of circumbinary planets by lowering harmful radiation and atmospheric erosion.

Contribution

It introduces a mechanism where binary star tidal effects can enhance habitability by decreasing stellar activity, supported by case studies of Kepler circumbinary planets.

Findings

Main sequence twin binaries can improve habitable conditions if synchronized early.

Wide, moist habitable zones around solar-like binaries support multiple planets.

Some binaries like Kepler 16 are inhospitable due to high XUV flux.

Abstract

We report a mechanism capable of reducing (or increasing) stellar activity in binary stars, thereby potentially enhancing (or destroying) circumbinary habitability. In single stars, stellar aggression towards planetary atmospheres causes mass-loss, which is especially detrimental for late-type stars, because habitable zones are very close and activity is long lasting. In binaries, tidal rotational breaking reduces magnetic activity, thus reducing harmful levels of XUV radiation and stellar mass-loss that are able to erode planetary atmospheres. We study this mechanism for all confirmed circumbinary (p-type) planets. We find that main sequence twins provide minimal flux variation and in some cases improved environments, if the stars rotationally synchronize within the first Gyr. Solar-like twins, like Kepler 34 and Kepler 35, provide low habitable zone XUV fluxes and stellar wind pressures. These wide, moist, habitable zones may potentially support multiple habitable planets. Solar-type stars with lower mass companions, like Kepler 47, allow for protected planets over a wide range of secondary masses and binary periods. Kepler 38 and related binaries are marginal cases. Kepler 64 and analogues have dramatically reduced stellar aggression due to synchronization of the primary, but are limited by the short lifetime. Kepler 16 appears to be inhospitable to planets due to extreme XUV flux. These results have important implications for estimates of the number of stellar systems containing habitable planets in the Galaxy and allow for the selection of binaries suitable for follow-up searches for habitable planets.