Stable habitable zones of single Jovian planet systems

Abstract

With continued improvement in telescope sensitivity and observational techniques, the search for rocky planets in stellar habitable zones is entering an exciting era. With so many exoplanetary systems available for follow-up observations to find potentially habitable planets, one needs to prioritise the ever-growing list of candidates. We aim to determine which of the known planetary systems are dynamically capable of hosting rocky planets in their habitable zones, with the goal of helping to focus future planet search programs. We perform an extensive suite of numerical simulations to identify regions in the habitable zones of single Jovian planet systems where Earth mass planets could maintain stable orbits, specifically focusing on the systems in the Catalog of Earth-like Exoplanet Survey Targets (CELESTA). We find that small, Earth-mass planets can maintain stable orbits in cases where the habitable zone is largely, or partially, unperturbed by a nearby Jovian, and that mutual gravitational interactions and resonant mechanisms are capable of producing stable orbits even in habitable zones that are significantly or completely disrupted by a Jovian. Our results yield a list of 13 single Jovian planet systems in CELESTA that are not only capable of supporting an Earth-mass planet on stable orbits in their habitable zone, but for which we are also able to constrain the orbits of the Earth-mass planet such that the induced radial velocity signals would be detectable with next generation instruments.

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

“…Since our simulations use massless TPs, they do not take into account mutual gravitational interactions between the planet and any companion -represented by the TPs -orbit. In order to use TPs to predict the stability of massive bodies with any confidence (such as demonstrated by Agnew et al 2017Agnew et al , 2018b, we only need to consider those TPs that are not excited (in other words, the gravitational influence of the known exoplanet is not destabilising it). The gravitational influence of the less massive Earth-mass planet is also unlikely to perturb the known exoplanet in this scenario.…”

“…Using n-body simulations, we can make dynamical predictions of regions in the (a,e) parameter space where additional planets will definitely be unstable. This formed the core of our previous work in this series (Agnew et al 2017(Agnew et al , 2018a, where we were able to identify systems that could potentially host dynamically stable HZ planets. Here, we extend that work to develop a stability mapping process that will enable future studies to quickly identify the regions in newly discovered exoplanetary systems where planets can definitely be ruled out, on dynamical grounds, as well as those regions where additional planets could only exist under very specific conditions (such as when trapped in a mutual mean-motion resonance with another planet, e.g.…”

“…By relaxing the criteria of our search to instead look for multiple planet systems where at least one planet is comparable in mass to Earth and resides in its host star's HZ (Kasting et al 1993;Kopparapu et al 2013Kopparapu et al , 2014Kane et al 2016), we will still yield exoplanetary systems that share several similarities with our own system, and are still candidates for further study from the perspective of planetary habitability. Additionally, we consider the notion that the observational bias inherent to several detection methods (Wittenmyer et al 2011;Dumusque et al 2012) can be interpreted to suggest that systems with massive, giant planets may also coexist with smaller, rocky exoplanets that so far have been undetectable due to detection limits (Agnew et al 2017). Indeed, given the challenges involved in finding habitable exo-Earths, it might be the case that such planets exist within known exoplanetary systems, lurking below our current threshold for detectability.…”

“…Giuppone et al 2013;), or numerically (e.g. Raymond & Barnes 2005;Jones et al 2005;Rivera & Haghighipour 2007;Jones & Sleep 2010;Wittenmyer et al 2013;Agnew et al 2017). Such studies have resulted in the development of several methods that allow exoplanetary systems to be assessed by planetary architectures as they are observed today (Giuppone et al 2013;Carrera et al 2016;Matsumura et al 2016;Agnew et al 2018a).…”

“…It has been frequently demonstrated that a variety of resonant mechanisms are often integral in determining the dynamical stability of a system (e.g. Wittenmyer et al 2012;Gallardo 2014;Kane 2015;Gallardo et al 2016;Mills et al 2016;Luger et al 2017;Delisle 2017;Agnew et al 2017Agnew et al , 2018b. Typically, such studies examine a single exoplanetary system, and study it in some depth to determine whether it is truly dynamically stable, and whether other planets could lurk undetected within it.…”