Evidence for Hidden Nearby Companions to Hot Jupiters

Abstract

The first discovered extrasolar worlds—giant, “hot Jupiter” planets on short-period orbits—came as a surprise to solar system–centric models of planet formation, prompting the development of new theories for planetary system evolution. The near absence of observed nearby planetary companions to hot Jupiters has been widely quoted as evidence in support of high-eccentricity tidal migration, a framework in which hot Jupiters form further out in their natal protoplanetary disks before being thrown inward with extremely high eccentricities, stripping systems of any close-in planetary companions. In this work, we present new results from a search for transit timing variations across the full 4 yr Kepler data set, demonstrating that at least 12% ± 6% of hot Jupiters have a nearby planetary companion. This subset of hot Jupiters is expected to have a quiescent dynamical history such that the systems could retain their nearby companions. We also demonstrate a ubiquity of nearby planetary companions to warm Jupiters (≥70% ± 16%), indicating that warm Jupiters typically form quiescently. We conclude by combining our results with existing observational constraints to propose an “eccentric migration” framework for the formation of short-period giant planets through postdisk dynamical sculpting in compact multiplanet systems. Our framework suggests that hot Jupiters constitute the natural end stage for giant planets spanning a wide range of eccentricities, with orbits that reach small enough periapses—either from their final orbital configurations in the disk phase or from eccentricity excitation in the postdisk phase—to trigger efficient tidal circularization.

TOI-1859b: A 64 Day Warm Jupiter on an Eccentric and Misaligned Orbit

“…TOI-1859b's eccentric and misaligned orbit, likely a result of planet-planet interactions, is consistent with the host star metallicity-eccentricity trend found in Dawson & Murray-Clay (2013). It is also consistent with the "eccentric migration" framework proposed by Wu et al (2023): multiple gas giants are more likely to form around metal-rich stars and can dynamically interact to excite their orbital eccentricities and mutual inclinations. Furthermore, TOI-1859 is a hot star with an effective temperature of 6341 70 68 -+ K. It is yet unclear if the temperature-stellar obliquity trend found in hot Jupiter systems (Schlaufman 2010;Winn et al 2010) is also true in warm Jupiter systems.…”

The Spin–Orbit Misalignment of TOI-1842b: The First Measurement of the Rossiter–McLaughlin Effect for a Warm Sub-Saturn around a Massive Star

“…We observed the R-M effect using the NEID spectrograph (Schwab et al 2016) on the WIYN 3.5 m telescope. The measured obliquity helps demonstrate the framework for an alternative explanation for the origins and evolution of spin-orbit misalignments based on the idea of dynamical excitement (Wu et al 2023). In this framework, initial planet multiplicity is the key tracer of misalignments, and the ability for planet-planet interactions is the key mechanism that is capable of exciting obliquity.…”

TOI-3984 A b and TOI-5293 A b: Two Temperate Gas Giants Transiting Mid-M Dwarfs in Wide Binary Systems

“…This low planetary multiplicity rate for hot Jupiters orbiting Sun-like stars has been statistically confirmed with multiple ground-and space-based transiting samples (e.g., Steffen et al 2012;Huang et al 2016;Maciejewski 2020;Hord et al 2021;Wang et al 2021;Zhu & Dong 2021). A search for transit timing variations in the Kepler sample by Wu et al (2023) also determined that a minimum of ∼13% of hot Jupiters orbiting Sun-like stars have nearby companions and must have a quiescent formation history. The scarcity of short-period companions to hot Jupiters is consistent with the hypothesis that high-eccentricity migration is responsible for most of these systems, as the inward migration of a gas giant is a dynamically "hot" process that would destabilize interior planets and leave an isolated gas giant (e.g., Mustill et al 2015;Dawson & Johnson 2018).…”