In Situ Formation and Dynamical Evolution of Hot Jupiter Systems

Hot Jupiters, giant extrasolar planets with orbital periods shorter than ∼10 days, have long been thought to form at large radial distances, only to subsequently experience long-range inward migration. Here, we offer the contrasting view that a substantial fraction of the hot Jupiter population formed in situ via the core-accretion process. We show that under conditions appropriate to the inner regions of protoplanetary disks, rapid gas accretion can be initiated by super-Earth-type planets, comprising 10–20 Earth masses of refractory material. An in situ formation scenario leads to testable consequences, including the expectation that hot Jupiters should frequently be accompanied by additional low-mass planets with periods shorter than ∼100 days. Our calculations further demonstrate that dynamical interactions during the early stages of planetary systems’ lifetimes should increase the inclinations of such companions, rendering transits rare. High-precision radial velocity monitoring provides the best prospect for their detection.