Letter to the Editor

Shallowness of circulation in hot Jupiters

Advancing the Ohmic dissipation model

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, Heidelberg 69117, Germany
e-mail: knierim@mpia.de
² Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA

Received: 5 November 2021
Accepted: 19 January 2022

Abstract

The inflated radii of giant short-period extrasolar planets collectively indicate that the interiors of hot Jupiters are heated by some anomalous energy dissipation mechanism. Although a variety of physical processes have been proposed to explain this heating, recent statistical evidence points to the confirmation of explicit predictions of the Ohmic dissipation theory, elevating this mechanism as the most promising candidate for resolving the radius inflation problem. In this work, we present an analytic model for the dissipation rate and derive a simple scaling law that links the magnitude of energy dissipation to the thickness of the atmospheric weather layer. From this relation, we find that the penetration depth influences the Ohmic dissipation rate by an order of magnitude. We further investigate the weather layer depth of hot Jupiters from the extent of their inflation and show that, depending on the magnetic field strength, hot Jupiter radii can be maintained even if the circulation layer is relatively shallow. Additionally, we explore the evolution of zonal wind velocities with equilibrium temperature by matching our analytic model to statistically expected dissipation rates. From this analysis, we deduce that the wind speed scales approximately as 1/√(T_eq−T₀), where T₀ is a constant that equals T₀ ∼ 1000 K − 1800 K depending on planet-specific parameters (radius, mass, etc.). This work outlines inter-related constraints on the atmospheric flow and the magnetic field of hot Jupiters and provides a foundation for future work on the Ohmic heating mechanism.