ETHANE ABUNDANCE ON TITAN

Ethane (C2H6) abundance in Titan's stratosphere is determined from rec ent ground based high spectral resolution measurements of individual e thane emission line spectra. Lines near 12 mu m in the v(9) band of C2 H6, were measured at a resolving power of lambda/Delta lambda similar to 10(6) with infrared heterodyne spectroscopy at the NASA Infrared Te lescope Facility (IRTF). Globally averaged constant-with-height C2H6 m ole fractions are retrieved for various possible thermal profiles on T itan. A range of possible stratospheric temperatures is investigated w ith respect to the data and a corresponding range of acceptable global ly averaged ethane mole fractions is retrieved, The data and physical constraints imposed by the observations limit the temperatures in Tita n's upper stratosphere to 160-180K. Corresponding acceptable mole frac tions can range from 4 x 10(-6) to 1.6 x 10(-5) depending on the therm al profile used. For a currently ''recommended'' thermal profile a mol e fraction of 9.4(-4.7, +9.4) x 10(-6) is retrieved, somewhat lower th an previous results, but centrally placed in the acceptable temperatur e-abundance parameter space. Published by Elsevier Science Ltd.