Prof. Patrick Irwin

Abstract:

In its first two years of operation since arrival at Jupiter in December 1995, the Near Infrared Mapping spectrometer (NIMS) on the Galileo orbiter spacecraft obtained extensive coverage of the planet, including detailed coverage of the north equatorial belt (NEB) 'hot spot' region and the Great Red Spot. We will present the current state of data analysis including recent results on the abundances and variability of several minor constituents (H2O, CH4, NH3, GeH4, CH3D and PH3) and the cloud structure and morphology. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Abstract:

This paper considers the rationale for the exploration of Saturn's atmosphere by the Cassini mission, taking account of the key scientific questions posed by the earlier investigation by Voyager, and the capabilities of the instrumentation making up the Cassini payload. While by no means all objectives can be addressed by this particular configuration, in particular without a Saturn entry probe, if everything goes according to plan important progress should be possible on a number of key objectives. (C) 1998 Elsevier Science Ltd. All rights reserved.

Abstract:

This paper presents the analysis of hot spot observations in the Jovian North Equatorial Belt obtained with the near-infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft. The data were acquired during the closest approach sequences between June 1996 and April 1997. We focus on the spectral window between 4.5 and 5.2 [Jim determining the cloud opacity above 2 bar, the water vapor relative humidity, and the ammonia abundance between 4 and 8 bar. We find a linear relationship between the cloud opacity and the continuum level of the spectrum. For a given radiance level of an individual spectrum, significant variations in the water vapor relative humidity are seen. However, no clear evidence for a relationship between the cloud opacity and the water relative humidity is seen. A cloud structure similar to that measured by the Galileo entry probe, with no significant cloud opacity below 2 bar, is adequate. The air in the hot spots is found to be overall dry, consistent with the probe measurements. None of the considered spectra show water vapor relative humidities exceeding 10%. Significant spatial variations of the water vapor relative humidity are found, and the distribution over the observed hot spot regions is complex. Because of a low sensitivity of the NIMS spectra to ammonia, uncertainties in the derived ammonia abundance are much higher than for water. There is, however, a possible trend in all the observed hot spots toward more ammonia inside than outside the hot spots at the sounded pressure levels. Copyright 1998 by the American Geophysical Union.