Direct measurement of winds on Titan

Abstract

We report the first direct measurement of wind velocity in the atmosphere of Titan, one of only two examples in our solar system of a slowly-rotating body with a dense atmosphere and a prime target of the Cassini mission. Zonal wind velocity was determined from Doppler shift of ethane lines emitted from Titan's stratosphere (∼0.1-7 mbar) measured by infrared heterodyne spectroscopy near 12 µm (λ/Δ λ ≥ 10⁶). Prograde zonal circulation, in the direction of global rotation, is established with 94% statistical confidence. Results provide information regarding Titan meteorology constraining dynamical theories for slowly-rotating bodies, provide otherwise unobtainable data to optimize the Cassini Huygens Probe investigations, and demonstrate the capability for remotely measuring winds on a small, distant object.