On turbulence driven by axial precession and tidal evolution of the spin-orbit angle of close-in giant planets

Abstract

The spin axis of a rotationally deformed planet is forced to precess about its orbital angular momentum vector, due to the tidal gravity of its host star, if these directions are misaligned. This induces internal fluid motions inside the planet that are subject to a hydrodynamic instability. We study the turbulent damping of precessional fluid motions, as a result of this instability, in the simplest local computational model of a giant planet (or star), with and without a weak internal magnetic field. Our aim is to determine the outcome of this instability, and its importance in driving tidal evolution of the spin-orbit angle in precessing planets (and stars). We find that this instability produces turbulent dissipation that is sufficiently strong that it could drive significant tidal evolution of the spin-orbit angle for hot Jupiters with orbital periods shorter than about 10-18 days. If this mechanism acts in isolation, this evolution would be towards alignment or anti-alignment, depending on the initial angle, but the ultimate evolution (if other tidal mechanisms also contribute) is expected to be towards alignment. The turbulent dissipation is proportional to the cube of the precession frequency, so it leads to much slower damping of stellar spin-orbit angles, implying that this instability is unlikely to drive evolution of the spin-orbit angle in stars (either in planetary or close binary systems). We also find that the instability-driven flow can act as a system-scale dynamo, which may play a role in producing magnetic fields in short-period planets.

13 pages, 9 figures, 1 table, accepted for publication in MNRAS (2016 May 12)

References in corpus (12)

• Tidal dissipation in stars and giant planets
• Early UV Ingress in WASP-12b: Measuring Planetary Magnetic Fields
• Magnetic moment and plasma environment of HD 209458b as determined from Ly$\alpha$ observations
• Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters
• Optical hydrogen absorption consistent with a thin bow shock leading the hot Jupiter HD 189733b
• Shear-driven parametric instability in a precessing sphere
• The BANANA project. V. Misaligned and precessing stellar rotation axes in CV Velorum
• Constraining the Oblateness of Kepler Planets
• Are Tidal Effects Responsible for Exoplanetary Spin-Orbit Alignment?
• Transit light curve and inner structure of close-in planets
• Nonlinear tides in a homogeneous rotating planet or star: global simulations of the elliptical instability
• Tidally driven dynamos in a rotating sphere

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• Inviscid instabilities in rotating ellipsoids on eccentric Kepler orbits
• Turbulent kinematic dynamos in ellipsoids driven by mechanical forcing
• Influence of stellar structure, evolution and rotation on the tidal damping of exoplanetary spin-orbit angles
• Interplay between geostrophic vortices and inertial waves in precession-driven turbulence
• Precessional angular velocity and field strength in the complex octonion space
• Precession-driven flows in stress-free ellipsoids
• The global flow state in a precessing cylinder
• The interactions of the elliptical instability and convection
• Spin Dynamics of Extrasolar Giant Planets in Planet-Planet Scattering
• Geophysical flows over topography, a playground for laboratory experiments
• Bursting of columnar structures in forced rotating turbulence
• Did lunar tides sustain the early Earth's dynamo?
• The stability of propagating plane inertial waves in rotating fluids
• The EBLM Project XVIII. 3D Obliquities of Five Low-Mass Eclipsing Binaries