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Jason Perry
Precis
Research Paper
September 11, 2000
For five years, the Galileo spacecraft has been orbiting the giant planet Jupiter taking images and spectra of Jupiter and its moons. The main focus of the mission has been the four large moons: Io, Europa, Ganymede, and Callisto. All of these moons have been seen up close, except one, Io. This changed in late 1999 when Galileo flew up close to Io three times. This allowed for high resolution images and spectra of Io for the first time. "A Close-Up Look at Io from Galileo’s Near-Infrared Mapping Spectrometer" describes the spectra that were taken of Io during these flybys (Science, 19 May 2000: 1201-1204).
According to Rosaly Lopes-Gautier, S. Douté, W.D. Smythe, L.W. Kamp, R.W. Carlson, A.G. Davies, F.E. Leader, A.S. McEwen, P.E. Geissler, S.W. Kieffer, L. Keszthelyi, E. Barbinis, R. Mehlman, M. Segura, J. Shirley, and L.A. Soderblom, one of Galileo’s major scientific goals is "to investigate Io’s volcanoes and their surface modification processes through high resolution spectral images" (1201). To complete this objective, they say, the Near-Infrared Mapping Spectrometer or NIMS took 31 observations of Io during three flybys of Io in late 1999 and early 2000. Due to an instrument problem, the NIMS was not able to complete all of its spectral observations, but it was able to obtain information on Io’s volcanoes and to map the SO2 frost on the surface. To get this information on Io, the instrument observed both Io’s own thermal emissions and reflected sunlight, they state.
The thermal component was modeled using two different temperatures, the brightness temperature and the color temperature, the latter usually showing warmer lava, they observe. They also state that SO2 was mapped by looking at the reflected sunlight part of the spectra, especially at 4.1 microns.
The authors of this article describe the results of observations of several volcanoes, including Loki Patera, Prometheus, Culann Patera, Tvashtar Catena, Tohil Patera, and several fainter volcanoes, or hot spots. According to the authors, Loki was shown to have a warm caldera floor with a temperature of 32ºF according to its brightness temperatures. The authors also observed a feature in the middle of the caldera resembling an island crisscrossed by several lava flows. These lava flows in this "island" were shown by the instruments to have a temperature of 170ºF in color temperature, the authors describe. The authors also say that most of the lava seen in the crack was erupted in an eruption in September 1999 and the lava on the caldera floor came from an earlier eruption.
NIMS also observed Prometheus and Tvashtar Catena, according to the authors. The authors state that these observations showed that both were highly active during the flyby with both having more than one hot spot or active volcanic region. According to Lopes-Gautier and the other authors, Tvashtar had a temperature of 1060 K during a flyby in November 1999 when a lava fountain was observed by SSI (Galileo’s visual and near infrared camera) and ground-based observations. Prometheus had several hotspots with the westernmost one being the coolest, according to the authors and NIMS data. This area of lava is also the origin of a gas plume that forms when newly emplaced lava interacts with the SO2 snowfield that surrounds the lava, state the authors. Observations of Prometheus also show a large ring of high concentrations of SO2 around Prometheus, observed the authors. However, this ring did not correspond with a bright ring seen in visual images as was expected, the authors noted.
Other volcanoes were observed by NIMS, the authors describe. These new observations allowed the authors to observe the complex structure of these volcanoes. Culann Patera, states the authors, was shown to have two hot spots, one at the patera itself, and the other at end of long lava flow. The authors also state that some volcanoes varied in activity, like Chaac Patera, which was shown to be inactive in October 1999 and active in November 1999. Finally, the authors demonstrate that the red deposits surrounding Culann Patera may contain SO2 in addition to the sulfur as had been shown before.
