Titan's stratospheric zonal wind, temperature, and ethane abundance a year prior to Huygens insertion

Abstract

Saturn's satellite, Titan, may have stratospheric winds up to ~210 m/s, circling Titan in ~1 terrestrial day compared to its 16-day rotation. Theoretical models explaining such super-rotating winds are not well constrained by observations of Titan or a similar slow rotator, Venus. We report measurements taken in December 2003 of zonal wind near Titan's equatorial region, including the Cassini Huygens probe entry latitude. Super-rotating prograde zonal winds of 190 +/- 90 m/s near 220 km altitude are found from Doppler-shifted C₂H₆ gas emission near 12 μm, confirming high wind velocity even near the equator. Stratospheric temperature constraints and ethane abundance (8 +/- 3 ppm) also are retrieved. Results are not inconsistent with earlier measurements and with recent Cassini CIRS results, but indicate possible variations between Titan's hemispheres. Differences in east and west C₂H₆ spectral line shapes can be accounted for by different vertical distributions of either C₂H₆ abundance or temperature or by unidentified dynamical effects.