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J. P. Hoffman, P. G. Steffes (Georgia Institute of Technology)
We are currently conducting low-temperature measurements of centimeter-wavelength opacity and refractivity of phosphine (PH3) in an H2/He atmosphere. Measurements are being made at 1.5 GHz (20 cm), 2.2 GHz (13.3 cm), 8.3 GHz (3.6 cm), 13.3 GHz (2.3 cm), and 21.6 GHz (1.4 cm) over a range of pressures and at temperatures of 213 K and 173 K. The experimental method is similar to that previously described by DeBoer and Steffes (Astrophys. and Space Sci. 236, 111-124, 1996). Preliminary results indicate that current theories significantly understate the centimeter-wavelength opacity of PH3. Together with our previous room temperature measurements (Hoffman, Steffes, and DeBoer, Icarus August 1999), these data will further elucidate the interpretation of centimeter-wavelength observations from radio telescopes and previous spacecraft (Voyager) radio occultation measurements of the atmospheres of all four Jovian planets with emphasis on Saturn and Neptune. These data will also aid future radio-scientific studies to be conducted by Cassini at Saturn. Further experiments are planned to distinguish between self-broadening and foreign gas broadening by using a test gas mixture with a different mixing ratio of PH3. This will facilitate development of a formalism for accurately determining the expected opacity from phosphine as a function of temperature, pressure, frequency, and mixing ratio.
This work is supported by the NASA Planetary Atmospheres Program under grant NAG5-4190.
The author(s) of this abstract have provided an email address for comments about the abstract: james.hoffman@ee.gatech.edu