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The Galileo Probe Atmosphere Structure Instrument will make in-situ measurements of the temperature and pressure profiles of the atmosphere of Jupiter, starting at about 10−10 bar level, when the Probe enters the upper atmosphere at a velocity of 48 km s−1, and continuing through its parachute descent to the 16 bar level. The data should make possible a number of inferences relative to atmospheric and cloud physical processes, cloud location and internal state, and dynamics of the atmosphere. For example, atmospheric stability should be defined, from which the convective or stratified nature of the atmosphere at levels surveyed should be determined and characterized, as well as the presence of turbulence and/or gravity waves. Because this is a rare opportunity, sensors have been selected and evaluated with great care, making use of prior experience at Mars and Venus, but with an eye to special problems which could arise in the Jupiter environment. The temperature sensors are similar to those used on Pioneer Venus; pressure sensors are similar to those used in the Atmosphere Structure Experiment during descent of the Viking Landers (and by the Meteorology Experiment after landing on the surface); the accelerometers are a miniaturized version of the Viking accelerometers. The microprocessor controlled experiment electronics serve multiple functions, including the sequencing of experiment operation in three modes and performing some on-board data processing and data compression.

The objective of the Nephelometer Experient aboard the Probe of the Galileo mission is to explore the vertical structure and microphysical properties of the clouds and hazes in the atmosphere of Jupiter along the descent trajectory of the Probe (nominally from 0.1 to > 10 bars). The measurements, to be obtained at least every kilometer of the Probe descent, will provide the bases for inferences of mean particle sizes, particle number densities (and hence, opacities, mass densities, and columnar mass loading) and, for non-highly absorbing particles, for distinguishing between solid and liquid particles. These quantities, especially the location of the cloud bases, together with other quantities derived from this and other experiments aboard the Probe, will not only yield strong evidence for the composition of the particles, but, using thermochemical models, for species abundances as well. The measurements in the upper troposphere will provide ‘ground truth’ data for correlation with remote sensing instruments aboard the Galileo Orbiter vehicle. The instrument is carefully designed and calibrated to measure the light scattering properties of the particulate clouds and hazes at scattering angles of 5.8°, 16°, 40°, 70°, and 178°. The measurement sensitivity and accuracy is such that useful estimates of mean particle radii in the range from about 0.2 to 20 μ can be inferred. The instrument will detect the presence of typical cloud particles with radii of about 1.0 μ, or larger, at concentrations of less than 1 cm3.

This paper describes our current understanding of the organization of the nodulation genes in a strain of R. leguminosarum, the species that nodulates peas, Vicia, Lens and Lanthyrus. In many of the fast-growing species of Rhizobium it is well established that the genes for nodulation and nitrogen fixation are clustered on large “symbiotic” plasmids one of which is the R. leguminosarum plasmid pRL 1JI whose transfer to other species of Rhizobium allows the transconjugants to nodulate peas (Johnston et al., 1978). Further, a region, no more than 10kb in size, was sufficient to confer the ability to nodulate peas when transferred to a strain of R. phaseoli cured of its resident symbiotic plasmid (Downie et al., 1983). The fact that the nodulation and host-range genes of pRL1JI are clustered within such a small region means that they can be analysed in considerable detail using both genetical and physical techniques.