%0 Journal Article
%T An intense thermospheric jet on Titan
%J -
%D 2019
%R https://doi.org/10.1038/s41550-019-0749-4
%X The presence of winds in Titan＊s lower and middle atmosphere has been determined by a variety of techniques, including direct measurements from the Huygens Probe1 over 0每150ˋkm; Doppler shifts of molecular spectral lines in the optical, thermal infrared and millimetre ranges2,3,4, which together have probed the ~100每450ˋkm altitude range; inferences from the thermal field over 10每0.001ˋmbar (that is, ~100每500ˋkm)5,6; and inferences from central flashes in stellar occultation curves7,8,9. These measurements predominantly indicated strong prograde winds, reaching maximum speeds of ~150每200ˋmˋsˋ1 in the upper stratosphere, with important latitudinal and seasonal variations. However, these observations provided incomplete atmospheric sounding; in particular, the wind regime in Titan＊s upper mesosphere and thermosphere (500每1,200ˋkm) has remained unconstrained so far. Here we report direct wind measurements based on Doppler shifts of six molecular species observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We show that contrary to expectations, strong prograde winds extend up to the thermosphere, with the circulation progressively turning into an equatorial jet regime as the altitude increases, reaching ~340ˋmˋsˋ1 at 1,000ˋkm. We suggest that these winds may represent the dynamical response of forcing by waves launched at upper stratospheric/mesospheric levels and/or of magnetospheric每ionospheric interaction. We also demonstrate that the distribution of the hydrogen isocyanide (HNC) molecule is restricted to Titan＊s thermosphere above ~870ˋkm altitude
%U https://www.nature.com/articles/s41550-019-0749-4