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L. Mayo (Raytheon ITSS), R. Samuelson (Department of Astronomy, University of Maryland)
Analysis of the 250 – 560 cm-1 spectral continuum of Titan’s north polar hood just after spring equinox reveals a tenuous but relatively uniform cloud of small particles permeating the lower stratosphere at altitudes between 58 and 90 km. Voyager 1 IRIS data suggest the particles are highly scattering, almost certainly condensed organics, with radii between 1 and 5 \mum. Mole fractions for the condensed material range between 4 X 10-8 and 4 X 10-6, depending upon particle size. Vapor pressure arguments imply condensed nitriles near 90 km, the most likely being HCN, with condensed hydrocarbons such as C2H6 restricted to regions considerably nearer the tropopause. No direct chemical identification is possible. Negligible methane supersaturation in the troposphere at 67.4 deg N latitude, when compared with degrees of supersaturation at other latitudes, hints at precipitation fluxes of north polar stratospheric condensates during the previous northern winter that were perhaps three orders of magnitude greater than those at low latitudes during that time. A scale height of 1.5 times the density scale height above 160 km is reaffirmed for the photochemical aerosol of the north polar hood. An aerosol mole fraction ~ 8 X 10-8 at 160 km is inferred, about 33% greater than the value derived in a previous study. There appears to be a depletion of aerosol somewhere below 160 km, possibly related to scavenging by precipitating condensates during the previous winter. The Cassini CIRS instrument, with its expanded spectral range and higher spectral resolution, should be able to provide highly complimentary information for the time period covering most of the northern winter season.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.