Hot Jupiters Predicted to Have Distant, Massive Cosystem Exoplanets

HOT JUPITERS FROM COPLANAR HIGH-ECCENTRICITY MIGRATION

Author:

Petrovich

Abstract:

We study the possibility that hot Jupiters (HJs) are formed through the secular gravitational interactions between two planets in eccentric orbits with relatively low mutual inclinations ($\lesssim 20{}^\circ $) and friction due to tides raised on the planet by the host star. We term this migration mechanism Coplanar High-eccentricity Migration (CHEM) because, like disk migration, it allows for migration to occur on the same plane in which the planets formed. CHEM can operate from the following typical initial configurations: (i) the inner planet in a circular orbit and the outer planet with an eccentricity $\gtrsim 0.67$ for ${{m}_{{\rm in}}}/{{m}_{{\rm out}}}{{({{a}_{{\rm in}}}/{{a}_{{\rm out}}})}^{1/2}}\lesssim 0.3$; (ii) two eccentric ($\gtrsim 0.5$) orbits for ${{m}_{{\rm in}}}/{{m}_{{\rm out}}}{{({{a}_{{\rm in}}}/{{a}_{{\rm out}}})}^{1/2}}\lesssim 0.16$. A population synthesis study of hierarchical systems of two giant planets using the observed eccentricity distribution of giant planets shows that CHEM produces HJs with low stellar obliquities ($\lesssim 30{}^\circ $), with a semi-major axis distribution that matches the observations, and at a rate that can account for their observed occurrence. A different mechanism is needed to create large obliquity HJs, either a different migration channel or a mechanism that tilts the star or the protoplanetary disk. CHEM predicts that HJs should have distant ($a\gtrsim 5$ AU) and massive (most likely ~1–3 times more massive than the HJ) companions with relatively low mutual inclinations ($\lesssim 20{}^\circ $) and moderately high eccentricities ($e\sim 0.2-0.5$).