Mathematics – Logic
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.2204g&link_type=abstract
American Astronomical Society, DPS meeting #28, #22.04; Bulletin of the American Astronomical Society, Vol. 28, p.1142
Mathematics
Logic
1
Scientific paper
One of the most surprising results of the Galileo probe was certainly the lack of water in Jupiter's atmosphere. The abundance of water measured around 10 bars, only 0.2 times the solar value [Niemann et al. Science 272, 846 (1996)], is far below the value of the bulk abundance estimated from studies of the interior and of thermochemistry. It is unlikely that water is depleted due to a phase transition deep inside the planet because the gravitational moments of the planet suggest that the molecular envelope of the planet is rich in elements other than H and He, compared to the Sun. The most likely explanation is therefore that water is hidden deeper than probed by Galileo because of a meteorological phenomenon. It has been suggested that the probe has fallen into a rare dry region. Results obtained from radio-occultation experiments on Uranus and Neptune, in the region where methane condenses in these planets, suggest another explanation: water in Jupiter, as methane in Neptune (and marginally in Uranus) may be buried deeper than expected in a significant part of the planet. The relative absence of water down to at least 10 bars would therefore be the rule rather than the exception. The effect of the negative buoyancy of moist air in hydrogen/helium atmosphere is excepted to be an important parameter to explain this phenomenon [Guillot Science 269, 1697 (1995)]. Physically plausible methane abundance profiles in the 0.3-5 bar region of the atmospheres of Uranus and Neptune were obtained by reanalysing the refractivity profiles acquired by Voyager 2 during radio-occultation of these planets. It is shown that, when the abundance of methane is equal to the bulk abundance of the planet, as constrained by spectroscopic measurement, the relative humidity is about 80% in Uranus and only 10% in Neptune. In other words, the pressure level at which the bulk abundance is attained is larger than predicted by the saturation curve, by about 5% in Uranus and 75% in Neptune. Jupiter is expected to be more similar to Neptune because in both planets, radiation can transport little of the planetary heat flux.
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