Stability of the directly imaged multiplanet system HR 8799: resonance and masses

A new era of directly imaged extrasolar planets has produced a three-planet system (Marois et al. 2008), where the masses of the planets have been estimated by untested cooling models. We point out that the nominal circular, face-on orbits of the planets lead to a dynamical instability in ~10^5 yr, a factor of at least 100 shorter than the estimated age of the star. Reduced planetary masses produce stability only for unreasonably small planets (
Comment: 16 pages; 15 figures; 4 tables. Accepted to ApJ. New version gives more attention to the upper mass limit for a double resonance. A new section allows for arbitrary eccentricities, orientations, and mutual inclinations