Pervasive Orbital Eccentricities Dictate the Habitability of Extrasolar Earths

TL;DR

This paper investigates how the presence of stellar companions and gas giant planets influences the orbital eccentricities of Earth-like exoplanets, which in turn affects their long-term habitability.

Contribution

It provides analytic criteria and numerical simulations to identify initial conditions leading to eccentric orbits in systems with multiple planets and stellar companions.

Findings

Stellar companions can excite planetary eccentricities significantly.

Gas giant planets' positions critically influence Earth-like planet eccentricities.

Eccentricity evolution impacts the potential habitability of exoplanets.

Abstract

The long-term habitability of Earth-like planets requires low orbital eccentricities. A secular perturbation from a distant stellar companion is a very important mechanism in exciting planetary eccentricities, as many of the extrasolar planetary systems are associated with stellar companions. Although the orbital evolution of an Earth-like planet in a stellar binary is well understood, the effect of a binary perturbation to a more realistic system containing additional gas giant planets has been very little studied. Here we provide analytic criteria confirmed by a large ensemble of numerical integrations that identify the initial orbital parameters leading to eccentric orbits. We show that an extra-solar earth is likely to experience a broad range of orbital evolution dictated by the location of a gas-giant planet, necessitating more focused studies on the effect of eccentricity on the potential for life.