Jupiter's Atmosphere: A Direct Link between Water Vapor and Cloud Activity

Paris, May 10, 2000

An international team has just shown that the convective clouds present in Jupiter's atmosphere are associated with atmospheric zones that are very humid. In Jupiter's atmosphere, a direct link therefore exists between water vapor circulation and cloud activity. These findings were obtained with the Near Infrared Mapping Spectrometer (NIMS) on board the NASA Galileo space probe, and were published in Nature on May 11, 2000.

Since the observations by the NASA probes Voyager in 1979 and Galileo in 1995, the issue of water on Jupiter has remained a major and poorly understood atmospheric physics problem. The direct measurements taken by the Galileo descent module in December 1995 showed an atmosphere that was drier than predicted. This was because the entry site was at a specific zone of the atmosphere referred to as a "hot spot," having specific meteorological conditions, a sort of "desert of Jupiter" (CNRS-INFO No. 333; 1/12/96 available in pdf: www.cnrs.fr/presse). Since then, further observations by the Galileo probe in orbit around Jupiter have made it possible to add to this description.

Several Jupiter hot spots were first studied using the Near-Infrared Mapping Spectrometer (NIMS), in comparison with the direct measurements taken by the descent module. This confirmed that these regions are both relatively cloud-free and also dry. More recently, images of specific, very active clouds have revealed an association between these clouds and storm activity, corresponding to humid convection movements. Analogous to tropical storms, these storm clouds over Jupiter convey large quantities of water vapor. Water condensation in the cold upper atmosphere of Jupiter generates, as on Earth, a charge separation leading to the production of lightning.

The international team including Pierre Drossart, researcher at the "Département de recherche spatiale" [Department of Space Research] (a joint CNRS-Observatoire de Paris research unit) and co-investigator on NIMS, has just completed this study of Jupiter's atmosphere (cf publication in Nature). By means of the NIMS, the astronomers simultaneously obtained infrared images of Jupiter, as with the Earth observation satellite SPOT, and also spectra that, through their signatures, identify the atmospheric components such as methane, ammonia, and water vapor. For the first time, the data thus collected shows that the previously described convective clouds are associated with highly localized and very humid atmospheric zones. This is the "missing link" between water vapor circulation and cloud activity. This relationship, although it was expected in simple meteorological models of the atmosphere, had never been shown directly before.

Although these observations do not solve the problem of the quantity of deep water on Jupiter, which remains inaccessible to observations, they do enable connections to be made between the visible meteorological phenomena in deeper layers of Jupiter's atmosphere. The near-infrared data from the NIMS probes the atmosphere to a pressure level of 5 bars, whereas the visible observations give information only on the clouds situated at pressures of 3 bars. By pursuing such studies on Jupiter's atmosphere, researchers hope that it will be possible to understand the exact links between the global meteorological circulation of that planet and the convective activity.

The team is made up of: M. Roos-Serote from the Lisbon Observatory; A.R. Vasavada, L. Kamp and R. W. Carlson from the Jet Propulsion Laboratory; P. Drossart from the "Département de recherche spatiale" [Department of Space Research] (CNRS-Observatoire de Paris); P. Irwin and C. Nixon from Oxford University.

References: "Proximate humid and dry regions in Jupiter's atmosphere indicate complex local meteorology," M. Roos-Serote, A.R. Vasavada, L. Kamp , P. Drossart, P. Irwin, C. Nixon, R. W. Carlson; Nature, May 11, 2000

Scientific contact:
Pierre Drossart.
Observatoire de Paris.
Tel: +33 1 45 07 76 64
e-mail: Pierre.Drossart@obspm.fr

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Fax : +33 1 44 96 49 93
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