There are a number of lines of observational evidence for the existence of one or more distant, massive planets in the solar system. Although the most readily apparent and most studied are the orbits of the extreme TNOs, as observed, we investigate a number of complementary dynamical mechanisms that can be used to constrain the masses and orbits that distant planets could have.
We first investigate the short-term tidal perturbations on other solar system bodies that yield measurable signatures in astrometric and range observations. In particular, we have examined the influence of a distant planet on the astrometry of Pluto, as well as on the precise range observations of the Cassini spacecraft. These investigations can be extended to GAIA astrometry and to range observations of other spacecraft.
Next we consider the physical mechanisms that explain the clustering observed in both actual extreme TNO orbits, as well as in numerical simulations of the outer solar system. By developing a detailed understanding of what determines the long-term stability, dynamical chaos, and diffusion of extreme TNO orbits, as perturbed by a massive, distant planet, we can better understand the range of masses and orbits that such a planet could have.
