In situ thermal conductivity measurements of Titan's lower atmosphere

Abstract

Thermal conductivity measurements, presented in this paper (Fig. 3), were made during the descent of the Huygens probe through the atmosphere of Titan below the altitude of 30 km. The measurements are broadly consistent with reference values derived from the composition, pressure and temperature profiles of the atmosphere; except in narrow altitude regions around 19 km and 11 km, where the measured thermal conductivity is lower than the reference by 1% and 2% respectively. Only single data point exists at each of the two altitudes mentioned above; if true however, the result supports the case for existence for molecules heavier than nitrogen in these regions (such as: ethane, other primordial noble gases, carbon dioxide, and other hydrocarbon derivatives). The increasing thermal conductivity observed below 7 km altitude could be due to some liquid deposition during the descent; either due to condensation and/or due to passing through layers of fog/cloud containing liquid nitrogen-methane. Thermal conductivity measurements do not allow conclusions to be drawn about how such liquid may have entered the sensor, but an estimate of the cumulative liquid content encountered in the last 7 km is 0.6% by volume of the Titan's atmosphere sampled during descent.

A Thermal Inertia Map of Titan

“…This leads to a similar value of conductivity for the organic sands to that derived by Schurmeier and Dombard (; 0.025 W/(mK)). However, we also take into account the thermal inertia of the atmosphere filling the void space between sand grains, which Hathi et al () calculated from Huygens measurements to be 0.015 W/(mK) at the surface. Ephemeral surface liquids may well appear in the equatorial dessert (Barnes et al, ; Lorenz et al, ; Turtle et al, ) and temporarily increase the effective thermal inertia, but we assume dry sands for this thermal inertia map to capture the more general thermal behavior of the dunes.…”