A Thermal Inertia Map of Titan

• Published in: Journal of geophysical research. Planets 2019-07, Vol.124 (7), p.1728-1742
• Main Authors: MacKenzie, Shannon M., Lora, Juan M., Lorenz, Ralph D.
• Format: Article
• Language: English
• Subjects: Atmospheric models; Cassini mission; Computer simulation; Convection; Diurnal variations; General circulation models; Global temperatures; Hydrologic cycle; Hydrologic models; Hydrologic processes; Hydrology; Inertia; Infrared spectrometers; Lakes; Local climates; Mapping; Moon; Morphology; Physical properties; Radar; Radar data; Regional climates; Saturn; Specific heat; Temperature distribution; Thermal inertia; Thermal properties; Thermodynamic properties; Titan; Titan atmosphere models; Wind profiles
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2019JE005930

Like Earth, the atmosphere of Titan, Saturn's largest moon, is affected by the ability of the surface to store and release heat. Modeling efforts have shown that global temperature distributions and wind profiles differ between simulations describing Titan's surface with a uniform thermal inertia. Cassini‐Huygens demonstrated, however, that a variety of morphologies and compositions make up the Titanian landscape. Using data from Cassini RADAR and the Visible and Infrared Mapping Spectrometer, we classified the surface into five terrain types: dune, lake, hummocky, plains, and labyrinth. We estimated the thermal and physical properties (conductivity, specific heat, and density) for each type, creating a 1° × 1° global map of thermal inertia values. For the lakes, as the depth of convection is not yet known, we considered both still and convective bodies. Four simulations of the Titan Atmospheric Model were run with different surface thermal properties: a low homogeneous thermal inertia, a moderate homogeneous, the heterogeneous map with still lakes, and the heterogeneous map with convective lakes. In dry regimes (i.e., without the hydrological cycle), the differences between the four cases were generally minimal, suggesting that general circulation models can use a single (moderate) value for surface thermal inertia value for large‐scale investigations that do not consider diurnal variations. Given the importance of hydrological processes and regional spatial diversity on Titan, future work should consider the effects of nonuniform thermal inertia on Titan's climate on local and regional scales. Key Points Titan's heterogeneous surface morphologies and compositions suggest a diversity of thermal inertia values Large‐scale investigations by general circulation models can use a single‐valued moderate thermal inertia Regional and diurnal variations probably warrant considering heterogeneous thermal inertia