The oblique orbit of the super-neptune HAT-P-11b

We find the orbit of the Neptune-sized exoplanet HAT-P-11b to be highly inclined relative to the equatorial plane of its host star. This conclusion is based on spectroscopic observations of two transits, which allowed the Rossiter-McLaughlin effect to be detected with an amplitude of 1.5ms ^-1. The sky-projected obliquity is 103⁺²⁶ _-10 deg. This is the smallest exoplanet for which spin-orbit alignment has been measured. The result favors a migration scenario involving few-body interactions followed by tidal dissipation. This finding also conforms with the pattern that the systems with theweakest tidal interactions have thewidest spread in obliquities.We predict that the high obliquity ofHAT-P-11 will be manifest in transit light curves from theKepler spacecraft: starspot-crossing anomalieswill recur at most once per stellar rotation period, rather than once per orbital period as they would for a well-aligned system.