The low electrical conductivity of Titan's lower atmosphere

Abstract

Titan's near-surface atmosphere, with a relatively high density and with weak ion production by cosmic rays or other sources, likely has a lower electrical conductivity than the Earth's, possibly <1 fS/m. Direct measurements by the Relaxation Probe on Huygens constrain it to be <0.5 pS/m, and extrapolation from higher altitudes suggests orders of magnitude lower than this. We investigate why several published models indicate much higher conductivity: it appears that aerosol removal of electrons may have been underestimated, and photoelectron emission from aerosols may have been overestimated. We propose a simple analytic description of the negative conductivity profile of the form Log10(σ) = A + B*z*exp(−[z/C]^D) with A = -15, B = 0.15, C = 100 km, D = 1.5 where z is the altitude (0–150 km) and σ is the negative ion/electron conductivity in S/m.Some local enhancement of conductivity at the surface may occur due to radiocarbon in recent surface deposits, and a significant perturbation may result from the radioisotope power source on the Dragonfly rotorcraft lander. We consider, and cannot dismiss completely, the hypothesis that the high conductivity of surface material measured by the Huygens probe, and its sudden reduction 11 min after landing, may have been associated with a wind change altering the abundance of nearby ions produced by radiation from the probe's Radioisotope Heater Units.