Dynamical Constraints on the Origin of Hot and Warm Jupiters With Close Friends

Abstract

Gas giants orbiting their host star within the ice line are thought to have migrated to their current locations from farther out. Here we consider the origin and dynamical evolution of observed Jupiters, focusing on hot and warm Jupiters with outer friends. We show that the majority of the observed Jupiter pairs (20 out of 24) are dynamically unstable if the inner planet is placed at 1 au distance from the stellar host. This finding is at odds with formation theories that invoke the migration of such planets from semimajor axes 1 au due to secular dynamical processes (e.g., secular chaos, Lidov-Kozai [LK] oscillations) coupled with tidal dissipation. In fact, the results of N-body integrations show that the evolution of dynamically unstable systems does not lead to tidal migration but rather to planet ejections and collisions with the host star. This and other arguments lead us to suggest that most of the observed planets with a companion could not have been transported from farther out through secular migration processes. More generally, by using a combination of numerical and analytic techniques, we show that the high-e LK migration scenario can only account for less than 10% of all gas giants observed between 0.1 and 1 au. Simulations of multiplanet systems support this result. Our study indicates that rather than starting on highly eccentric orbits with orbital periods above 1 yr, these "warm" Jupiters are more likely to have reached the region where they are observed today without having experienced significant tidal dissipation.

On the formation of hot and warm Jupiters via secular high-eccentricity migration in stellar triples

“…This result is similar to previous studies of high-e migration in stellar binaries (e.g. Petrovich & Tremaine 2016;Antonini et al 2016), and in multiplanet systems (Hamers et al 2016a). …”

Eccentric Companions to Kepler-448b and Kepler-693b: Clues to the Formation of Warm Jupiters

“…A similar issue has also been discussed for WJs with outer planetary-mass companions (Antonini et al 2016): the outer orbits in these systems, if primordial, are in most cases too small for the inner WJs to have migrated from 1 au. In addition, population synthesis simulations of high-eccentricity migration from 1 au, either via the companion on a wide orbit (Anderson et al 2016;Petrovich & Tremaine 2016) or secular chaos in multiple systems (Hamers et al 2017), have difficulty in producing a sufficient number of WJs relative to HJs.…”

In situ scattering of warm Jupiters and implications for dynamical histories

“…Such a configuration is difficult to produce in a violent high-eccentricity migration scenario. Furthermore, Antonini et al (2016) examined the subset of observed WJs with characterized (in terms of mass, semimajor axis and eccentricity) external giant planet companions, and found that most systems are inconsistent with a 1 exoplanets.org, accessed July 4, 2019. 2 When dynamical (chaotic) tides are incorporated into the higheccentricity migration model, highly eccentric (e 0.9) WJs form rapidly, and subsequently circularize to become HJs .…”