Radiation and Plasma Environment of the Kepler Circumbinary Habitable Zone Planets

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable Zone Planets

Authors:

Zuluaga et al

Abstract:

The remarkable discovery of many planets and candidates using the Kepler telescope even includes ten planets orbiting eight binaries. Three out of the eight, Kepler 16, Kepler 47, and KIC 9632895, have at least one planet in the circumbinary habitable zone (BHZ). In previous work (Mason et al. 2013), we investigated the potential habitability of Earth-like circumbinary planets. In particular, we highlighted the role of mutual stellar tidal interaction and the resulting impact on terrestrial planet habitability. The Kepler binaries with planets in the BHZ are studied in order to constrain the high energy radiation and plasma environment of potentially habitable circumbinary planets. The limits of the BHZ in these binaries as a function of time are estimated and the habitability lifetime is calculated. A self-consistent model of the evolution of stellar rotation including the effect of tidal interaction is key to establishing the plasma and radiation environment. A comprehensive model of the evolution of stellar activity and radiation properties, as proxies for stellar aggression towards planetary atmospheres is developed. We find that Kepler-16 has had a plasma environment favorable for the survival of atmospheres of Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47 making its radiation environment less harsh than solar system and a good example of the mechanism first proposed by Mason et al. (2013). KIC-9632895 has a plasma and radiation environment similar to that of solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ.

KIC 9632895b: A Circumbinary 6.2 Earth-radius Superearth/Mini Neptune

KIC 9632895 - The 10th Kepler Transiting Circumbinary Planet

Authors:

Welsh et al

Abstract:

We present the discovery of KIC 9632895b, a 6.2 Earth-radius planet in a low-eccentricity, 240.5-day orbit about an eclipsing binary. The binary itself consists of a 0.93 and 0.194 solar mass pair of stars with an orbital period of 27.3 days. The plane of the planet's orbit is rapidly precessing, and its inclination only becomes sufficiently aligned with the primary star in the latter portion of the Kepler data. Thus three transits are present in the latter half of the light curve, but none of the three conjunctions that occurred during the first half of the light curve produced transits. The precession period is ~103 years, and during that cycle, transits are visible only ~8% of the time. This has the important implication that for every system like KIC 9632895 that we detect, there are ~12 circumbinary systems that exist but are not currently exhibiting transits. The planet's mass is too small to noticeably perturb the binary, consequently its mass is not measurable with these data; but our photodynamical model places a 1-sigma upper limit of 16 Earth masses. With a period 8.8 times that of the binary, the planet is well outside the dynamical instability zone. It does, however, lie within the habitable zone of the binary, and making it the third of ten Kepler circumbinary planets to do so.