Titan's stratospheric temperature asymmetry: a radiative origin?

Area of Science:

• Planetary Science
• Atmospheric Science
• Astrobiology

Background:

• Titan's stratosphere exhibits a notable thermal asymmetry, with colder northern latitudes during the Voyager 1981 spring equinox encounter.
• This asymmetry contradicts expectations based on a symmetrical distribution of radiative sources and sinks.

Purpose of the Study:

• To investigate the radiative budget of Titan's stratosphere and explain the observed thermal asymmetry.
• To determine the contributions of gas and haze composition to the temperature differences between northern and southern latitudes.

Main Methods:

• Analysis of Voyager IRIS spectra from symmetric northern and southern latitudes.
• Computation of cooling and solar heating rate profiles using derived gas and haze abundances.

Main Results:

• Northern latitudes (50°N) are 7-13 K colder than southern latitudes (53°S) in the 0.1-5 mbar range.
• The northern stratosphere is enriched in nitriles and hydrocarbons, with twice the haze optical depth compared to the south.
• Despite lower temperatures, northern cooling rates are 20-40% higher due to increased infrared radiators.

Conclusions:

• Latitudinal variations in gas and haze composition are sufficient to explain Titan's stratospheric temperature asymmetry.
• Enhanced solar heating in the north, due to increased haze absorbance or particle density, further contributes to the asymmetry.
• Dynamical heat transport may play a role but is not necessarily required to explain the observed temperature gradients.