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J.P. Hoffman, P.G. Steffes, D.R. DeBoer (Georgia Inst. of Tech.)
It has been suggested that phosphine (PH3) may contribute significantly to the microwave emission spectrum of Neptune, and to the centimeter-wavelength opacity measured by the Voyager 2 spacecraft at Neptune (DeBoer and Steffes, ICARUS 123, 324-335, 1996). As a result, laboratory measurements of the microwave opacity and refractivity of PH3 in an H2/He atmosphere are being conducted 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) at pressures of 1, 3, and 5 Bars. The experimental approach is similar to that previously used by DeBoer and Steffes (Astrophys. and Space Sci. 236, 111-124, 1996) utilizing the Georgia Tech high sensitivity microwave measurment system. Preliminary results at room temperature indicate that current theories significantly understate the centimeter-wavelength opacity of PH3. This appears to be most drastic at the longer wavelengths (13.3 and 20 cm).
This higher-than-expected opacity will further elucidate the interpretation of centimeter-wavelength microwave observations from radio telescopes and previous spacecraft (Voyager) radio occulation measurements of the atmospheres of all four Jovian planets. These data will also serve to aid future interpretation of entry probe signal attenuation measurements from the Galileo probe, and from Cassini radioscientific studies at Saturn. Further experiments will be conduced at ambient, 213K and 173K, at the same frequencies and pressures.
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: gt0412b@prism.gatech.edu