Predicting multiple planet stability and habitable zone companions in the TESS era

Abstract

We present an approach that is able to both rapidly assess the dynamical stability of multiple planet systems, and determine whether an exoplanet system would be capable of hosting a dynamically stable Earth-mass companion in its habitable zone. We conduct a suite of numerical simulations using a swarm of massless test particles in the vicinity of the orbit of a massive planet, in order to develop a predictive tool which can be used to achieve these desired outcomes. In this work, we outline both the numerical methods we used to develop the tool, and demonstrate its use. We find that the test particles survive in systems either because they are unperturbed due to being so far removed from the massive planet, or due to being trapped in stable mean motion resonant orbits with the massive planet. The resulting unexcited test particle swarm produces a unique signature in (a,e) space that represents the stable regions within the system. We are able to scale and translate this stability signature, and combine several together in order to conservatively assess the dynamical stability of newly discovered multiple planet systems. We also assess the stability of a system's habitable zone and determine whether an Earth-mass companion could remain on a stable orbit, without the need for exhaustive numerical simulations.

Science Extraction from TESS Observations of Known Exoplanet Hosts

“…One of the major reasons to continue monitoring known host stars is the prospect of detecting additional planets within those systems, regardless of the detection technique that was used to discover the known planets (Dietrich & Apai 2020). Continued monitoring and discovery of additional planets is an essential pathway toward revealing the full diversity of planetary architectures (Winn & Fabrycky 2015), including dynamical interactions (Kane & Raymond 2014;Agnew et al 2019) and coplanrity (Fang & Margot 2012;Becker et al 2017).…”

Dynamical Packing in the Habitable Zone: The Case of Beta CVn

“…Of particular interest are those planets that lie within the habitable zone (HZ) of their host stars, where liquid water may be present on the planetary surface given sufficient atmospheric pressure (Kasting et al 1993;Kopparapu et al 2013Kopparapu et al , 2014. Dynamics of planetary systems have been used to determine orbital effects in the HZ (Kane 2015;Agnew et al 2019), as well as potentially predicting additional HZ planets (Kopparapu et al 2009;Kopparapu & Barnes 2010). Several compact planetary systems have been discovered that harbor more than one planet in the HZ, including GJ667C (Anglada-Escudé et al 2013), TRAPPIST-1 (Gillon et al 2017;Luger et al 2017), and Teegarden's star (Zechmeister et al 2019).…”

Planet Hunters TESS III: two transiting planets around the bright G dwarf HD 152843

“…The minimum possible period of 19.25 days lies interior to the 1:2 resonance, and is close to the 3:5 resonance (period of 19.35 days). As can be seen in the fourth row of Figure 4 in Agnew et al (2019), this region is still likely to be stable, so long as the orbital eccentricity for planet c is below ∼ 0.2.…”

“…Horner et al (2019). However, we can estimate the system stability by comparing the possible period scenarios of planet c to the general cases presented by Agnew et al (2019).…”