Orbital Perturbations of Transiting Planets: A Possible Method to Measure Stellar Quadrupoles and to Detect Earth‐Mass Planets

Abstract

The recent discovery of a planetary transit in the star HD 209458, and the subsequent highly precise observation of the transit light curve with Hubble Space Telescope , is encouraging to search for any phenomena that might induce small changes in the light curve. Here we consider the effect of the quadrupole moment of the parent star and of a possible second planet perturbing the orbit of the transiting planet. Both of these cause a precession of the orbital plane and of the periastron of the planet, which result in a long-term variation of the duration and the period of the transits. For a transiting planet at 0.05 AU, either a quadrupole moment similar to that of the Sun or the gravitational tug from an Earth-like planet on an orbit of semimajor axis ~0.2 AU and a relative inclination near the optimal 45° would cause a transit duration time derivative of ~1 s yr -1 .