Warm Jupiters from secular planet-planet interactions

Image: Illustration of a warm Jupiter planet. Credit: X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS

Most warm Jupiters have pericenter distances that are too large for significant orbital migration by tidal friction.

In a recent paper (Petrovich & Tremaine 2016) the authors study the possibility that the warm Jupiters are undergoing secular eccentricity oscillations excited by an outer companion (a planet or star) in an eccentric and/or mutually inclined orbit.

In this model the warm Jupiters migrate periodically, in the high-eccentricity phase of the oscillation when the pericenter distance is small, but are typically observed at much lower eccentricities.

The authors show that the steady-state eccentricity distribution of the warm Jupiters migrating by this mechanism is approximately flat, which is consistent with the observed distribution if and only if we restrict the sample to warm Jupiters that have outer companions detected by radial-velocity surveys.

The eccentricity distribution of warm Jupiters without companions exhibits a peak at low eccentricities (e≲0.2) that must be explained by a different formation mechanism.

Based on a population-synthesis study they find that high-eccentricity migration excited by an outer planetary companion (i) can account for ∼20% of the warm Jupiters and most of the warm Jupiters with e≳0.4, a fraction that is consistent with the observed population of warm Jupiters with outer companions; (ii) can produce most of the observed population of hot Jupiters, with a semimajor axis distribution that matches the observations, but fails to account adequately for ∼60% of hot Jupiters with projected obliquities ≲20°.

Thus ∼20% of the warm Jupiters and ∼60% of the hot Jupiters can be produced by high-eccentricity migration. They also provide predictions for the expected mutual inclinations and spin-orbit angles of the planetary systems with hot and warm Jupiters produced by high-eccentricity migration.

Petrovich & Tremaine 2016 (preprint) - Warm Jupiters from secular planet-planet interactions - (arXiv)

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