The Global Polytropic Model Applied to Exoplanet Orbits

Gravitational quantization of exoplanet orbits in HD 10180, Kepler-32, Kepler-33, Kepler-102, and Kepler-186

Authors:

Geroyannis et al

Abstract:

The so-called "global polytropic model" is applied to the numerical study of the exoplanet systems HD 10180, Kepler-32, Kepler-33, Kepler-102, and Kepler-186. We compare computed distances of planets from their host stars with corresponding observations and discuss some further orbit predictions made by the model.

Tidal Evolution of Multiple Exoplanetary Systems Such as Kepler-62 & Kepler-186

Tidal evolution in multiple planet systems: application to Kepler-62 and Kepler-186

Authors:

Bolmont et al

Abstract:

A large number of observed exoplanets are part of multiple planet systems. Most of these systems are sufficiently close-in to be tidally evolving. In such systems, there is a competition between the excitation caused by planet-planet interactions and tidal damping. Using as an example two multiple planet systems, which host planets in the surface liquid water habitable zone (HZ): Kepler-62 and Kepler-186, we show the importance and effect of both planetary and stellar tides on the dynamical evolution of planets and on the climate of the HZ planets.

Modeling the Habitability of Kepler-186f

Formation, tidal evolution and habitability of the Kepler-186 system

Authors:

Bolmont et al

Abstract:

The Kepler-186 system consists of five planets orbiting an early-M dwarf. The planets have physical radii of 1.0-1.50 R⊕ and orbital periods of 4 to 130 days. The 1.1 R⊕ Kepler-186f with a period of 130 days is of particular interest. Its insolation of roughly 0.32 S⊙places it within the liquid water habitable zone. We present a multi-faceted study of the Kepler-186 system. First, we show that the distribution of planet masses can be roughly reproduced if the planets accreted from a high-surface density disk presumably sculpted by an earlier phase of migration. However, our simulations predict the existence of 1-2 undetected planets between planets e and f. Next, we present a dynamical analysis of the system including the effect of tides. The timescale for tidal evolution is short enough that the four inner planets must have small obliquities and near-synchronous rotation rates. Tidal evolution of Kepler-186f is slow enough that its current spin state depends on a combination of its dissipation rate and the stellar age. Finally, we study the habitability of Kepler-186f with a 1-D climate model. The planet's surface temperature can be raised above 273 K with 0.5-5 bars of CO2, depending on the amount of N2 present. Kepler-186f represents a case study of an Earth-sized planet in the cooler regions of the habitable zone of a cool star.

Kepler-186f's Paper

An Earth-Sized Planet in the Habitable Zone of a Cool Star

Authors:

Quintana et al

Abstract:

The quest for Earth-like planets is a major focus of current exoplanet research. Although planets that are Earth-sized and smaller have been detected, these planets reside in orbits that are too close to their host star to allow liquid water on their surfaces. We present the detection of Kepler-186f, a 1.11 ± 0.14 Earth-radius planet that is the outermost of five planets, all roughly Earth-sized, that transit a 0.47 ± 0.05 solar-radius star. The intensity and spectrum of the star’s radiation place Kepler-186f in the stellar habitable zone, implying that if Kepler-186f has an Earth-like atmosphere and water at its surface, then some of this water is likely to be in liquid form.