[Previous] | [Session 39] | [Next]
P.G. Steffes, P.N. Mohammed (Georgia Institute of Technology)
As described in an accompanying paper by Mohammed and Steffes (BAAS, DPS-02), new laboratory measurements of the 9 mm opacity of phosphine and ammonia under simulated conditions for Saturn have recently been completed. Using these results, plus previous results for the centimeter-wavelength opacity of these constituents (see, e.g., Hoffman et al. ICARUS 152, 172-184, 2001), studies of the sensitivity of the Cassini radio link to atmospheric constituents encountered during radio occultations are being conducted. Preliminary results suggest that for orbits with favorable occultation geometry, the Ka-Band (32 GHz, or 9.3 mm) downlink will encounter measurable absorption from PH3 at the 0.5 Bar pressure level, and will be capable of profiling phosphine down to altitudes with pressures up to 0.8 Bars, where the opacity from ammonia would then dominate followed by loss of signal (LOS) at about 0.9 Bars. As with the Voyager 2 radio occultation experiment, the X-Band (8.4 GHz, or 3.6 cm) downlink is expected to encounter measurable absorption at the 0.8 Bar pressure level from both PH3 and NH3, before losing the signal at the 1 Bar pressure level, and the S-Band (2.3 GHz or 13 cm) downlink is expected to encounter measurable absorption from both PH3 and NH3 at the 1.1 Bar pressure level with profiling capability down to the 1.6 Bar pressure level. A computer model to simulate the ray paths and attenuation encountered during Saturn occultations is currently under development.
This work is supported by the NASA Planetary Atmospheres Program under grant NAG5-12122.
If the author provided an email address or URL for general inquiries,
it is as follows:
Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.