Journal Article

A primordial origin for misalignments between stellar spin axes and planetary orbits

Batygin, Konstantin

2012

Overview

Modelling shows that the misaligned orbits of ‘hot Jupiters’ can follow naturally from disk migration in binary systems whose orbital plane is uncorrelated with the spin axes of the individual stars. Orbital disruption of 'hot Jupiter' exoplanets Recent planetary transit observations have shown that many 'hot Jupiter' exoplanets in close-in orbits are grossly misaligned with respect to the rotation axes of their host stars. This fact has cast doubt on a previously widely accepted model of disk-driven migration as the primary mechanism responsible for moving planetrs from an outer to an inner orbit. In this paper Konstantin Batygin demonstrates that disk-driven migration is not only capable of producing misaligned planets, it will produce them preferentially. The argument rests on the observation that most stars are born as binaries, and that the gravitational perturbations of the stellar companions act to twist the orbital planes of proto-planetary disks out of alignment with the rotation axes of their host stars. The existence of gaseous giant planets whose orbits lie close to their host stars (‘hot Jupiters’) can largely be accounted for by planetary migration associated with viscous evolution of proto-planetary nebulae 1 . Recently, observations of the Rossiter–McLaughlin effect 2 during planetary transits have revealed that a considerable fraction of hot Jupiters are on orbits that are misaligned with respect to the spin axes of their host stars 3 . This observation has cast doubt on the importance of disk-driven migration as a mechanism for producing hot Jupiters. Here I show that misaligned orbits can be a natural consequence of disk migration in binary systems whose orbital plane is uncorrelated with the spin axes of the individual stars 4 , 5 , 6 . The gravitational torques arising from the dynamical evolution of idealized proto-planetary disks under perturbations from massive distant bodies act to misalign the orbital planes of the disks relative to the spin poles of their host stars. As a result, I suggest that in the absence of strong coupling between the angular momentum of the disk and that of the host star, or of sufficient dissipation that acts to realign the stellar spin axis and the planetary orbits, the fraction of planetary systems (including systems of ‘hot Neptunes’ and ‘super-Earths’) whose angular momentum vectors are misaligned with respect to their host stars will be commensurate with the rate of primordial stellar multiplicity.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/766/33/445 / Angular momentum / Astronomy / Astrophysics / Disks / Earth / Earth, ocean, space / Exact sciences and technology / Extrasolar planetary systems / Extrasolar planets / Fundamental astronomy / Fundamental astronomy and astrophysics. Instrumentation, techniques, and astronomical observations / Humanities and Social Sciences / letter / Migration / multidisciplinary / Observations / Orbit determination and improvement / Orbitals / Orbits / Orbits (Astrophysics) / Planes / Rotation / Science / Stars / Stars & galaxies