A highly mutually inclined compact warm-Jupiter system KOI-984?

Abstract

The discovery of a population of close-orbiting giant planets (≤ 1 au) has raised a number of questions about their origins and dynamical histories. These issues have still not been fully resolved, despite over 20 years of exoplanet detections and a large number of discovered exoplanets. In particular, it is unclear whether warm Jupiters (WJs) form in situ, or whether they migrate from further outside and are even currently migrating to form hot Jupiters. Here, we report the possible discovery and characterization of the planets in a highly mutually inclined (Imut 45°) compact two-planet system (KOI-984), in which the newly discovered warm Jupiter KOI-984c is on a 21.5-d moderately eccentric (e 0.4) orbit, in addition to a previously known 4.3-d planet candidate KOI-984b. Meanwhile, the orbital configuration of a moderately inclined (Imut 15°) low-mass (mc 24M; Pb 8.6 d) perturbing planet near the 1:2 mean-motion resonance with KOI-984b could also well reproduce the observed transit-Timing variations and transit-duration variations of KOI-984b. Such an eccentric WJ with a close-in sibling would pose a challenge to the proposed formation and migration mechanisms of WJs if the first scenario is supported with more evidence in the near future; this system with several other well measured inclined WJ systems (e.g. Kepler-419 and Kepler-108) may provide additional clues to the origin and dynamical histories of WJs.