A class of warm Jupiters with mutually inclined, apsidally misaligned close friends
The orbits of giant extrasolar planets often have surprisingly small semimajor axes, large eccentricities, or severe misalignments between their orbit normals and their host stars' spin axes. In some formation scenarios invoking Kozai-Lidov oscillations, an external planetary companion drives a planet onto an orbit having these properties. The mutual inclinations for Kozai-Lidov oscillations can be large and have not been confirmed observationally. Here we present evidence that observed eccentric warm Jupiters with eccentric giant companions have mutual inclinations that oscillate between 35° and 65°. Our inference is based on the pairs’ observed apsidal separations, which cluster near 90°. The near-orthogonality of periapse directions is effected by the outer companion's quadrupolar and octupolar potentials. These systems may be undergoing a stalled version of tidal migration that produces warm Jupiters over hot Jupiters, and they provide evidence for a population of multiplanet systems that are not flat and have been sculpted by Kozai-Lidov oscillations. Numerical simulations of stalled nondisk migration replicate the observed lack of coplanarity for giant exoplanet pairs. Close planet friends get out of line Some “warm” giant exoplanets orbit much closer to their star than do similar planets in our solar system. Dawson and Chiang argue that understanding how such orbits have evolved can answer an outstanding question: How do “hot” giant planets (which are more common than these “warm” ones) get so close to their host star? These planets frequently have giant companions. Numerical simulations revealed that planets with an eccentric giant companion may have just the right mutual inclination for the inner planet to be pushed slowly toward the star. This process could then produce systems with “warm” rather than “hot” Jupiters. Science, this issue p. 212