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T. A. Livengood (Challenger Center), T. Kostiuk (NASA GSFC), G. Sonnabend (NAS NRC/GSFC), P. N. Romani, K. E. Fast (NASA GSFC), T. Hewagama (U of MD), J. N. Annen, D. Buhl (NASA GSFC)
Thermally-excited infrared emission from ethane (C2H6), formed in Saturn's southern (summer) stratosphere, was observed in February 2004 using line-resolved spectroscopy. Measured spectra were acquired at 15\circ intervals along Saturn's East limb, from 15\circ – 90\circ south at longitude offset from the central meridian selected to obtain a uniform viewing angle of 64\circ. Additional spectra were acquired on Saturn's southern auroral zone near the limb and at the central meridian, at \approx 78\circS latitude, testing for the presence at millibar pressures of zonal wind driven by ionospheric currents, as recently reported by Stallard et al. (Icarus 167, 204--211, 2004) for the nanobar-to-microbar pressure regime. The observations were conducted using the Goddard Space Flight Center Heterodyne Instrument for Planetary Wind And Composition (HIPWAC) at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. The spectrum obtained from the HIPWAC optical front-end was measured and recorded independently using an RF filter-bank system to obtain resolving power \lambda/\Delta\lambda = 1-5 \times 106 and by an acousto-optic spectrometer (AOS) system to obtain resolving power \lambda/\Delta\lambda = 25 \times 106, at 11.744 µm and at 11.816 µm wavelength. The detailed lineshape and the ratio of strong and weak line features separately constrain the temperature and ethane mole fraction within the region of line formation. These measurements complement the Cassini CIRS observation program for Saturn, which will have much higher spatial resolution and spectral bandwidth but much lower spectral resolving power than the present observations. These observations are part of an on-going program observing seasonal change in Saturn's stratosphere since 1989.
This work was supported by the NASA Planetary Astronomy Program.
The author(s) of this abstract have provided an email address for comments about the abstract: timothy.a.livengood@gsfc.nasa.gov
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.