Temperature and pressure at Saturnís cloud levels

Temperature and pressure at Saturnís cloud levels

Fig. 10.5 . The fading radio signals when the Voyager 1 and 2 spacecraft passed behind Saturn in 1980 and 1981, respectively, revealed the temperatures (bottom axis) and pressures (right axis) in its upper atmosphere. The temperature reaches a minimum of about 80 kelvin at a level called the tropopause where the atmospheric pressure is 0.1 bars, or 100 millibars. By way of comparison, the pressure of the Earthís atmosphere at sea level is 1.0 bar. The altitudes (left axis) are relative to the 0.1 bar level, and the dots are spaced to indicate tenfold changes in pressure. Solar radiation causes the temperature to increase with height just above the tropospause. At lower levels, the temperature and pressure increase systematically with depth. Three possible clouds layers of ammonia, NH3, ammonium hydrosulfide, NH4SH, and water ice, H2O, are shown. The altitudes of the predicted cloud layers are based on an equilibrium gaseous mixture that is of solar composition. An increase in abundance of a condensable gas by a factor of three would lower the altitude of the cloud base by about 10 kilometers.

Copyright 2010, Professor Kenneth R. Lang, Tufts University