Photolysis of methane and the ionosphere of Uranus

Abstract

Photochemical calculations for Uranus predict an extensive region of condensation of acetylene, ethane and methane in the vicinity of the temperature inversion layer. This could explain why ethane was not detected on Uranus, unlike Neptune which has a much warmer inversion layer. Subsequent snow-out of the condensibles is expected to result in reduced visibility in the troposphere. Ionospheric calculations for the equatorial region to be probed by Voyager, indicate peak electron concentrations on the order of 5 x 103 cm-3, if dynamical effects are important. Upper limit to the electron peak is 3 x 104 cm-3. Exospheric temperatures as high as 200-250K are conceivable.