The Occurrence of Additional Giant Planets Inside the Water-Ice Line in Systems with Hot Jupiters: Evidence Against High-Eccentricity Migration

TL;DR

This study investigates the presence of additional giant planets inside the water-ice line in systems with hot Jupiters, providing evidence that challenges the high-eccentricity migration theory for their formation.

Contribution

The paper presents observational evidence showing hot Jupiters are not more likely to have interior giant companions, contradicting predictions of the high-eccentricity migration scenario.

Findings

Hot Jupiters with P_orb < 10 days have similar companion occurrence rates as longer-period giants.

Presence of interior giant planets is common in hot Jupiter systems.

Results challenge the high-eccentricity migration hypothesis for hot Jupiter formation.

Abstract

The origin of Jupiter-mass planets with orbital periods of only a few days is still uncertain. It is widely believed that these planets formed near the water-ice line of the protoplanetary disk, and subsequently migrated into much smaller orbits. Most of the proposed migration mechanisms can be classified either as disk-driven migration, or as excitation of a very high eccentricity followed by tidal circularization. In the latter scenario, the giant planet that is destined to become a hot Jupiter spends billions of years on a highly-eccentric orbit, with apastron near the water-ice line. Eventually, tidal dissipation at periastron shrinks and circularizes the orbit. If this is correct, then it should be especially rare for hot Jupiters to be accompanied by another giant planet interior to the water-ice line. Using the current sample of giant planets discovered with the Doppler technique, we find that hot Jupiters with P_orb < 10 days are no more or less likely to have exterior Jupiter-mass companions than longer-period giant planets with P_orb >= 10 days. This result holds for exterior companions both inside and outside of the approximate location of the water-ice line. These results are difficult to reconcile with the high-eccentricity migration scenario for hot Jupiter formation.