Abstract: The search for extra-solar planets has led to the surprising discovery of many Jupiter-like planets in very close proximity to their host star, the so-called “hot Jupiters”(HJs). Even more surprising, many of these HJs have orbits that are eccentric or highly inclined with respect to the equator of the star, & some (about 25%) even orbiting counter to the spin direction of the star. This poses a unique challenge to all planet formation models. We show that secular interactions between Jupiter-like planet & another perturber in the system can easily produce retrograde HJ orbits. We show that in the frame of work of secular hierarchical triple system (the
so-called Kozai mechanism) the inner orbit’s angular momentum component parallel to the total angular momentum (i.e., the z-component of the inner orbit angular momentum) need not be constant. In fact, it can even change sign, leading to a retrograde orbit. A brief excursion to very high eccentricity during the chaotic evolution of the inner orbit allows planet-star tidal interactions to rapidly circularize that orbit, decoupling the
planets & forming a retrograde hot Jupiter. We estimate the relative frequencies of retrograde orbits & counter to the stellar spin orbits using Monte Carlo simulations, & find that they are consistent with the observations.