Pluto's extended atmosphere: An escape model and initial observations

We have calculated the rates of production and hydrodynamic outflow of atomic hydrogen resulting from the photodissociation of methane in the upper atmosphere of Pluto. Under the present near-perihelion conditions this yields an extended cloud of H around Pluto which is likely to be the most easily observable signature of Pluto's extended atmosphere, and thereby provide information on the extent, escape rate, and composition of Pluto's upper atmosphere. We have also performed initial observations with the IUE attempting to detect the H Ly [alpha] emission from the extended H cloud, which we use to derive upper limits to the cloud properties as a function of the cloud extent.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30226/1/0000618.pd

Io'S Atmospheric Freeze-Out Dynamics In The Presence Of A Non-Condensable Species

One dimensional direct simulation Monte Carlo (DSMC) simulations are used to examine the effect of a trace non-condensable species on the freeze-out dynamics of Io's sulfur dioxide sublimation atmosphere during eclipse and egress. Due to finite ballistic times, essentially no collapse occurs during the first 10 minutes of eclipse at altitudes above similar to 100 km, and hence immediately after ingress auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the sublimation SO2 atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of a perfect non-condensable species due to the formation of a static diffusion layer several mean free paths thick near the surface. The higher the non-condensable mole fraction, the longer the collapse time. The effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined since real gas species may not be perfectly non-condensable at realistic surface temperatures. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics. If the sticking coefficient of the non-condensable exceeds similar to 0.25 the collapse dynamics are effectively the same as if there was no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size and the formation of an effective diffusion layer requires that the layer be stationary which does not occur if the surface is a sink. As the surface temperature increases during egress from eclipse the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the auroral emissions after egress.Aerospace Engineerin

Latitudinal Temperature Variations of Jovian H+3

A spectral image of Jupiter centred on 3.45 [mu]m, taken on the night of April 2, 1992, using cooled grating spectrometer CGS4 on the United Kingdom Infrared Telescope, shows that features due to the v2 ro-vibrational band of H+3 extend right across the planet. Analysis of these features indicates that the jovian disk may be divided into three regions--two mid-high latitude regions with temperatures around 800 K and a hotter, central region with a temperature around 1200 K. The central meridian longitude of the image in the jovian System III is 102[deg], coinciding with the region of the Lyman-[alpha] Bulge. The significance of new work on the bulge for understanding this image is discussed. The image also shows an interesting doublet centred on 3.52 [mu]m. Candidates for this feature are discussed; none is found to be satisfactory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31900/1/0000853.pd

Middle UV to Near-IR Spectrum of Electron-Excited SO2

We investigated the electron impact-induced fluorescence spectrum of SO2 to provide excitation cross sections for modeling Io's mission spectrum and analyzing Cassini Imaging Science Subsystem observations. The electron-excited middle-ultraviolet visible optical near-infrared (VOIR) emission spectrum of SO2 gas was generated in the laboratory and studied from 2000 to 11,000 A at a resolution of (Delta)(lamda) approximately 2.5 A full width at half maximum (FWHM). The VOIR laboratory spectrum longward of 6000 A consists entirely of S I, II and O I, II multiplets for electron impact energies above approximately 15 eV. Between 2000 and 6000 A, we find previously identified molecular bands from both SO and SO2. This work represents a significant improvement in spectral resolution over our earlier work done at 18 A FWHM. From a measurement of the medium-resolution spectrum, we provide detailed 25- and 100-eV emission cross sections for spectral features from 2000 to 11,000 A . On the basis of these data, we suggest future ground-based and satellite telescopic observations in the VOIR that are of promise for understanding Io's atmosphere