Survival and Detectability of Long Period Planets Beyond 100 AU

¹ Astronomy Department, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL 32111, USA
² California Institute of Technology, Department of Astronomy/Optical Observatories, 1200 E. California Blvd., MC 105-24, Pasadena, CA 91125, USA

Abstract

Direct imaging searches have begun to detect planetary and brown dwarf companions and to place constraints on the presence of giant planets at large separations from their host star. This work helps to motivate such planet searches by predicting a population of young giant planets that could be detectable by direct imaging campaigns. Both the classical core accretion and the gravitational instability model for planet formation are hard-pressed to form such planets in situ. Therefore, direct imaging searches have traditionally appealed to the possibility of in situ planet formation via a large scale gravitational instability. Here, we show that dynamical instabilities among planetary systems that originally formed multiple giant planets much closer to the host star could produce a population of giant planets at large separations. The number and distribution of such planets is a strong function of time, complicating the statistical analysis of direct imaging surveys. The number and radial distribution of such planets is related to the number of giant planets formed per host star and the timescale for the disk evolution. Thus, direct imaging programs with sufficient sensitivity and survey size could place interesting constraints on planet formation models.