The Time Dependence of hot Jupiters' Orbital Inclinations

Abstract: Via the Rossiter-McLaughlin effect, it is possible to measure the sky-projected angle between the stellar spin and a planet's orbital spin. Observed orbital inclinations have been found to range over all possible angles. A tentative detection of a correlation between the dispersion in spin/orbit angle and the youth of the system is revealed, using spin/orbit measurements for hot Jupiters around stars with masses larger than 1.2 Solar Masses for which age estimates are more accurately determined. The chance of this pattern arising by chance has been computed to 7%. This appears in accordance with tidal dissipation where non-coplanar hot Jupiters' orbits tidally realign. The results show they would do so within about 2.5 Gyr. For the considered sample, the results give support to hot Jupiters being placed on non coplanar orbits early in their history rather than this happening late. Such events could involve strong planet-planet scattering.