Gravitational atmospheric tides as a probe of Titan’s interior: Application to Dragonfly

¹ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92195 Meudon, France
e-mail: benjamin.charnay@obspm.fr
² Laboratoire de Planétologie et de Géodynamique, UMR 6112, CNRS, Université de Nantes, 2 rue de la Houssinière, BP 92208, 44322 Nantes cedex 03, France
³ Laboratoire de Météorologie Dynamique (LMD/IPSL), Sorbonne Université, ENS, PSL Research University, Ecole Polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France
⁴ Johns Hopkins Applied Physics Lab, Laurel, MD, USA

Received: 29 July 2021
Accepted: 3 November 2021

Abstract

Context. Saturn’s massive gravity is expected to causes a tide in Titan’s atmosphere, producing a surface pressure variation through the orbit of Titan and tidal winds in the troposphere. The future Dragonfly mission could analyse this exotic meteorological phenomenon.

Aims. We aim to analyse the effect of Saturn’s tides on Titan’s atmosphere and interior to determine how pressure measurements by Dragonfly could constrain Titan’s interior.

Methods. We model atmospheric tides with analytical calculations and with a 3D global climate model (the IPSL-Titan GCM), including the tidal response of the interior.

Results. We predict that the Love numbers of Titan’s interior should verify 1 + ℜ(k₂ − h₂) ~ 0.02–0.1 and ℑ(k₂ − h₂) < 0.04. The deformation of Titan’s interior should therefore strongly weaken gravitational atmospheric tides, yielding a residual surface pressure amplitude of only ~5 Pa, with a phase shift of 5–20 h. Tidal winds are very weak, of the order of 3 × 10⁻⁴ m s⁻¹ in the lower troposphere. Finally, constraints from Dragonfly data may permit the real and the imaginary parts of k₂ − h₂ to be estimated with a precision of ±0.01–0.03.

Conclusions. Measurements of pressure variations by Dragonfly over the whole mission could give valuable constraints on the thickness of Titan’s ice shell, and, via geophysical models, its heat flux and the density of its internal ocean.