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.
Highlights
Just as Saturn’s massive gravity causes tides both in Titan’s interior as well as its surface seas, it causes a tide in the atmosphere (Lorenz 1992; Tokano & Neubauer 2002; Strobel 2006)
Tokano & Neubauer (2002) analysed these gravitational atmospheric tides with a 3D global climate model (GCM). They found that the tidal potential produced by Saturn would generate a surface pressure variation of ∼1.3 hPa through the orbit of Titan and tidal winds in the troposphere, with a mean wind speed of ∼0.3– 0.4 m s−1 at 300 m
We considered interior structures consisting of four tude of the tidal pressure variations (∆Psurf = γ2ρ0V1) and phase main layers from centre to surface: a rocky core, a high-pressure compared to the sub-Saturnian point (ψ + ψ2), without interior
Summary
Just as Saturn’s massive gravity causes tides both in Titan’s interior as well as its surface seas, it causes a tide in the atmosphere (Lorenz 1992; Tokano & Neubauer 2002; Strobel 2006). Tokano & Neubauer (2002) analysed these gravitational atmospheric tides with a 3D global climate model (GCM) They found that the tidal potential produced by Saturn would generate a surface pressure variation of ∼1.3 hPa through the orbit of Titan and tidal winds in the troposphere, with a mean wind speed of ∼0.3– 0.4 m s−1 at 300 m. Walterscheid & Schubert (2006) suggested that the vertical transport by gravitational tides could produce the haze layers in Titan’s upper atmosphere These atmospheric studies did not take into account the deformation of Titan’s interior. Titan likely possesses an internal water-rich ocean, as suggested from the elevated Love number k2 ∼ 0.62 measured by the spacecraft Cassini (Iess et al 2012; Durante et al 2019) Such a large induced gravitational potential implies a large deformation of the interior, which should strongly impact atmospheric tides.
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