Highlight: Spin-orbit angle measurements for six southern transiting planets [...] (vol. 524)

Vol. 524In section 10. Planets and planetary systems22 November 2010

Spin-orbit angle measurements for six southern transiting planets. New insights into the dynamical origins of hot Jupiters

by A. H. M. J. Triaud, A. Collier Cameron, D. Queloz, et al., A&A 524, A25 alt

When an exoplanet transits its parent star, one should be able to determine the angle between the stellar spin axis and the axis of the planetary orbital plane by careful analysis of the radial velocity signal: this is called the Rossiter-Mac Laughlin effect. In our Solar System, this angle is at most 7° for all 8 planets. In the first transiting systems for which this measurement had been possible, the angles were found to be small, which is consistent with the situation in our Solar System. This picture slowly changed with the discovery of several highly inclined and even retrograde systems. Triaud et al. present six new observations of 3 systems that are highly inclined and three that are compatible with 0°. But accounting for the degeneracy in the inclination of the stellar spin axis determination, they show that between 45 and 85% of all hot Jupiters have inclinations of 30° or more. This implies that standard migration alone cannot explain the observations. They also show that the observations are explained by a model in which the planets are sent close to their star through a so-called Kozai mechanism (see figure).