Comparing methane and temperature profiles on Titan in 1980 and 2005

The Huygens Probe data provided a direct measurement of CH₄, temperature, and pressure in Titan's atmosphere. This data can be used to compare to the Voyager data in which the effects of CH₄, temperature, and pressure were mixed together. Comparison with Huygens data indicates that values of the surface relative humidity of CH₄ at the Voyager ingress and egress were between 20% and 45%, and values above 60% are inconsistent with this comparison. The most parsimonious explanation for the Voyager data is that the temperature and CH₄ surface humidity at the Voyager ingress and egress profiles were identical to the Huygens values; a surface temperature of 93.65±0.25 K, and a surface relative humidity of 43%. Thus, it is likely that these values have characterized the equatorial region of Titan from 1980 until 2005. The small reduction of 1 K, between the tropopause temperatures of the Voyager profiles and the tropopause temperature of the Huygens profile is explainable by a change in the antigreenhouse flux from the stratosphere from 0.13 to 0.1 of the total average solar flux. This could result from a small seasonal change in the optical properties of the stratospheric haze.