Dynamically hot Super-Earths from outer giant planet scattering

TL;DR

This paper uses N-body simulations to show that outer giant planet scattering can dynamically heat inner super-Earth systems, leading to hot, eccentric, and inclined single-transiting planets, explaining several Kepler observations.

Contribution

It introduces a model where outer giant planet scattering explains the hot, eccentric, and inclined nature of some single-transiting super-Earths observed by Kepler.

Findings

Outer giant planets reduce inner system multiplicity.

Surviving inner planets can have high eccentricities and inclinations.

Model explains Kepler's eccentricity and obliquity observations.

Abstract

The hundreds of multiple planetary systems discovered by the \textit{Kepler} mission are typically observed to reside in close-in ($\lesssim0.5$ AU), low-eccentricity, and low-inclination orbits. We run N-body experiments to study the effect that unstable outer ($\gtrsim1$ AU) giant planets, whose end orbital configurations resemble those in the Radial Velocity population, have on these close-in multiple super-Earth systems. Our experiments show that the giant planets greatly reduce the multiplicity of the inner super-Earths and the surviving population can have large eccentricities ($e\gtrsim0.3$) and inclinations ($i\gtrsim20^\circ$) at levels that anti-correlate with multiplicity. Consequently, this model predicts the existence of a population of dynamically hot single-transiting planets with typical eccentricities and inclinations %in the ranges of $\sim 0.1-0.5$ and $\sim 10^\circ-40^\circ$. We show that these results can explain the following observations: (i) the recent eccentricity measurements of \textit{Kepler} super-Earths from transit durations; (ii) the tentative observation that single-transiting systems have a wider distribution of stellar obliquity angles compared to the multiple-transiting systems; (iii) the architecture of some eccentric super-Earths discovered by Radial Velocity surveys such as HD\,125612c. Future observations from \textit{TESS} will reveal many more dynamically hot single transiting planets, for which follow up Radial Velocity studies will be able to test our models and see whether they have outer giant planets.