THE 3-DIMENSIONAL ARCHITECTURE OF THE ANDROMEDAE PLANETARY SYSTEM

The Upsilon Andromedae system is the rst exoplanetary system to have the relative inclination of two planets’ orbital planes directly measured, and therefore oers our rst window into the 3dimensional congurations of planetary systems. We present, for the rst time, full 3-dimensional, dynamically stable congurations for the 3 planets of the system consistent with all observational constraints. While the outer 2 planets, c and d, are inclined by 30 , the inner planet’s orbital plane has not been detected. We use N-body simulations to search for stable 3-planet congurations that are consistent with the combined radial velocity and astrometric solution. We nd that only 10 trials out of 1000 are robustly stable on 100 Myr timescales, or 8 billion orbits of planet b. Planet b’s orbit must lie near the invariable plane of planets c and d, but can be either prograde or retrograde. These solutions predict b’s mass is in the range 2 - 9 MJup and has an inclination angle from the sky plane of less than 25 . Combined with brightness variations in the combined star/planet light curve (\phase curve"), our results imply that planet b’s radius is 1:8 RJup, relatively large for a planet of its age. However, the eccentricity of b in several of our stable solutions reaches > 0:1, generating upwards of 10 19 watts in the interior of the planet via tidal dissipation, possibly inating the radius to an amount consistent with phase curve observations. Subject headings: planetary systems, planets and satellites: dynamical evolution and stability, stars: individual (Upsilon Andromedae)