Outlandish orbit of HAT-P-7b

We also report evidence for an additional planet or companion star. The evidence for the unparalleled orbit and the third body is based on precise observations of the star's apparent radial velocity (RV).

The anomalous RV due to rotation (the Rossiter-McLaughlin effect) was found to be a blueshift during the first half of the transit and a redshift during the second half, an inversion of the usual pattern, implying that the angle between the sky-projected orbital and stellar angular momentum vectors is 182.5{deg}+/-9.4{deg}. The third body is implicated by excess RV variation of the host star over 2yr. Some possible explanations for the tilted orbit of HAT-P-7b are a close encounter with another planet, the Kozai effect, and resonant capture by an inward-migrating outer planet.