Obliquity and Eccentricity Constraints For Terrestrial Exoplanets

TL;DR

This paper analyzes how obliquity and eccentricity influence the incident flux on terrestrial exoplanets, deriving criteria for their effects and applying these to known systems to inform climate modeling and potential observables.

Contribution

It introduces a criterion to compare flux variations caused by obliquity and eccentricity, and applies it to constrain planetary properties in multiple exoplanet systems.

Findings

Flux variation due to obliquity can match that from eccentricity under specific conditions.

Constraints on eccentricity for planets in four systems are derived from orbital dynamics.

Implications for climate modeling and detection of obliquity signatures are discussed.

Abstract

Exoplanet discoveries over recent years have shown that terrestrial planets are exceptionally common. Many of these planets are in compact systems that result in complex orbital dynamics. A key step toward determining the surface conditions of these planets is understanding the latitudinally dependent flux incident at the top of the atmosphere as a function of orbital phase. The two main properties of a planet that influence the time-dependent nature of the flux are the obliquity and orbital eccentricity of the planet. We derive the criterion for which the flux variation due to obliquity is equivalent to the flux variation due to orbital eccentricity. This equivalence is computed for both the maximum and average flux scenarios, the latter of which includes the effects of the diurnal cycle. We apply these calculations to four known multi-planet systems (GJ 163, K2-3, Kepler-186, and Proxima Centauri), where we constrain the eccentricity of terrestrial planets using orbital dynamics considerations and model the effect of obliquity on incident flux. We discuss the implications of these simulations on climate models for terrestrial planets and outline detectable signatures of planetary obliquity.