The Time Dependence of hot Jupiters' Orbital Inclinations

TL;DR

This study investigates how hot Jupiters' orbital inclinations evolve over time, suggesting early non-coplanar orbits tend to realign within a few billion years, supporting early dynamical interactions like planet-planet scattering.

Contribution

It provides evidence for a correlation between system age and orbital inclination dispersion, indicating early dynamical processes influence hot Jupiters' orbital alignments.

Findings

Orbital inclination dispersion correlates with system age.

Hot Jupiters tend to realign within about 2.5 billion years.

Early non-coplanar orbits support planet-planet scattering scenarios.

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.