The atmospheric composition and structure of Jupiter and Saturn from ISO observations: a preliminary review

Infrared spectra of Jupiter and Saturn have been recorded with the two spec trometers of the Infrared Space Observatory (ISO) in 1995-1998, in the 2.3- 180 mu m range. Both the grating modes (R = 150-2000) and the Fabry-Pi rot modes (R = 8000-30.000) of the two instruments were used. The main results of these observations are (1) the detection of water vapour in the deep tro posphere of Saturn; (2) the detection of new hydrocarbons (CH3C2H, C4H2, C6 H6, CH3) in Saturn's stratosphere; (3) the detection of water vapour and ca rbon dioxide in the stratospheres of Jupiter and Saturn; (4) a new determin ation of the D/H ratio from the detection of HD rotational lines. The origi n of the external oxygen source on Jupiter and Saturn (also found in the ot her giant planets and Titan in comparable amounts) may be either interplane tary (micrometeoritic flux) or local (rings and/or satellites). The D/H det ermination in Jupiter, comparable to Saturn's result, is in agreement with the recent measurement by the Galileo probe (Mahaffy, P.R., Donahue, T.M., Atreya, S.K., Owen, T.C., Niemann, H.B., 1998. Galileo probe measurements o f D/H and He-3/He-4 in Jupiters atmosphere. Space Science Rev. 84 251-263); the D/H values on Uranus and Neptune are significantly higher, as expected from current models of planetary formation. (C) 1999 Elsevier Science Ltd. All rights reserved.