Obliquity Evolution of the Potentially Habitable Exoplanet Kepler-62f

TL;DR

This study uses N-body simulations to analyze how obliquity variations of Kepler-62f, a potentially habitable exoplanet, depend on planetary system architecture and rotation, revealing conditions that could significantly affect its climate and habitability.

Contribution

It provides the first detailed analysis of obliquity evolution of Kepler-62f considering different system configurations and rotation periods, highlighting factors influencing climate stability.

Findings

Obliquity variations are generally limited to less than 10 degrees.

Outer gas giants can induce large obliquity swings up to 60 degrees.

Rotation period and orbital architecture critically affect climate variability.

Abstract

Variations in the axial tilt, or obliquity, of terrestrial planets can affect their climates and therefore their habitability. Kepler-62f is a 1.4 R$_\oplus$ planet orbiting within the habitable zone of its K2 dwarf host star (Borucki et al. 2013). We perform N-body simulations that monitor the evolution of obliquity of Kepler-62f for 10 million year timescales to explore the effects on model assumptions, such as the masses of the Kepler-62 planets and the possibility of outer bodies. Significant obliquity variation occurs when the rotational precession frequency overlaps with one or more of the secular orbital frequencies, but most variations are limited to $\lesssim$10$^\circ$. Moderate variations ($\sim$10$^\circ - 20^\circ$) can occur over a broader range of initial obliquities when the relative nodal longitude ($\Delta\Omega$) overlaps with the frequency and phase of a given secular mode. However, we find that adding outer gas giants on long period orbits ($\gtrsim$ 1000 days) can produce large ($\sim$60$^\circ$) variations in obliquity if Kepler-62f has a very rapid (4 hr) rotation period. The possibility of giant planets on long period orbits impacts the climate and habitability of Kepler-62f through variations in the latitudinal surface flux, where the timescale for large variation can occur on million year timescales.