Water on Giant Planets

As we have seen water is an important constituent of the giant planets besides hydrogen and helium. This was pointed out by Stevenson and Fishbein, 1981 [326]. The presence of water and other heavy molecules in the interiors of the giant planets may inhibit convection as a means of energy transport there. Guillot, 1995 [150] found that convection is inhibited in Uranus and Neptune when methane reaches an abundance of about 15 times the solar value and in Jupiter and Saturn if the abundance of water is more than about five times the solar value. Roos-Serote et al 2004 [280] studied the water abundance in the atmosphere of Jupiter by analysing the O/H ratio. This ratio was found compatible with one or more times the solar value. Water vapor is the main source for O (except some small contribution from CO). 

Water is present in Jupiter s atmosphere both in the troposphere and in the stratosphere. Observations of tropospheric water were made with the Kuiper Airborne Telescope and the IRIS (Infrared Interferometer Spectrometer and Radiometer) Spectrometer on board Voyager 1 and Voyager 2 From these data the vertical distribution of water in the level from 16 bar in Jupiter s troposphere was derived. A thin H2O ice cloud would form at 2 bars, T = 200 K (Bjoraker, Larson and Kunde, 1986 [30]). 

Observation of water vapor from satellite measurements at 557 GHz is reported by Bergin et al., 2000 [23]. The line appears to be formed at maximum pressures of about 5 mbar. Water is not uniformly mixed but increases with altitude above the condensation level. In Jupiter and Saturn, the amount of water implied by the data is 1.5-2.5 times larger than inferred from Infrared Space Observatory data. 

IRIS also revealed stratospheric water ice clouds (Simon-Miller, 2000 [311]). 

Abundance measurements of oxygen in Jupiter s atmosphere suggest that during its formation phase carbonaceous matter played a more important role than condensed ice. Therefore, Jupiter (and possibly Saturn) are found at the carbonaceous condensation/evaporation front (the tar line ) and the snow line was located farther out in the solar nebula (Lodders, 2004 [206]). This could also explain why Galileo probe measurements found much less water in Jupiter s atmosphere than expected. The snow line denotes the minimum radius from the Sun at which water ice could have condensed, at about 150 K, so it is the point in the solar nebula where water ice condenses. The tar line denotes the point where asphalt or tar-like material formed, pushing the snow line farther out in the solar nebula. 

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