Secular transport during disk dispersal: the case of Kepler-419

TL;DR

This paper proposes that the observed eccentric and anti-aligned orbits of Kepler-419's planets are caused by the gradual dispersal of its protoplanetary disk, which transports eccentricity and apsidal alignment through adiabatic evolution.

Contribution

It introduces a novel mechanism where disk dispersal drives secular transport of eccentricity and apsidal anti-alignment in non-resonant giant planet pairs.

Findings

Disk dispersal can produce high eccentricities in giant planets.

Apsidal anti-alignment can be maintained during disk dispersal.

The mechanism may explain hot Jupiter formation and observed eccentricities.

Abstract

Due to fortuitous circumstances, the two giant planets around Kepler-419 have well characterized 3-D orbits. They are nearly coplanar to each other; the inner one has a large eccentricity (~0.82); and the apses of the two orbits librate around anti-alignment. Such a state defies available proposals for large eccentricities. We argue that it is instead uniquely produced by a decaying protoplanetary disk. When the disk was massive, its precessional effect on the planets forced the two apses to center around an anti-aligned state. And as the disk is gradually eroded, the pair of planets are adiabatically transported to a new state where most of the eccentricity (or rather, the angular momentum deficit) is transferred to the inner planet, and the two apses are largely anti-aligned. During this transport, any initial mutual inclination may be reduced or enhanced; either may be compatible with the current constraints. So a primordial disk can drive up planet eccentricities both in resonant planet pairs (as has been shown for GJ 876) and in secularly interacting, non-resonant pairs. The mechanism discussed here may be relevant for forming hot Jupiters and for explaining the observed eccentricities of warm and cold giant planets.