Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.p22a..02m&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #P22A-02
Other
5462 Polar Regions, 5464 Remote Sensing, 6218 Jovian Satellites, 8450 Planetary Volcanism (5480)
Scientific paper
One of the most spectacular phenomena on Io are the active volcanic plumes. Nine plumes were observed during the Voyager 1 encounter in 1979: Pele (300 km high), Loki (150 km; 2 plumes), and 6 smaller "Prometheus-type" plumes. When Voyager 2 imaged Io 4 months later, all of the these plumes were detected except Pele, and there were two new large red plume deposits (Surt and Aten) similar to the deposits of Pele. These 2 new plume vents were at relatively high latitudes (45N and 48S) whereas the others were more equatorial. Galileo observed a total of 10 plumes prior to 2000, 4 of which were erupting from the same volcanic complexes as in 1979, so there was a total of 15 volcanic centers with observed plumes, all equatorial except Masubi at 44S. We found that Prometheus-type plumes wander, apparently erupting from rootless vents where silicate lava flows over volatile-rich ground. Red deposits, on the other hand, seem to mark the deep vents for silicate lava. Galileo and HST also showed that Pele is normally detectable only at UV wavelengths or at very high phase angles, and was in an anomalous state during the Voyager 1 encounter. The only good candidate for a "stealth" SO2 gas plume visible only in eclipse was seen over Acala, although some Prometheus-type plumes appeared much larger in eclipse. The existence of many much smaller plumes was predicted from Voyager observations of bright streaks radial to Pele, but Galileo has not confirmed this hypothesis. From the joint Galileo-Cassini observations within a few days of Jan 1, 2001 we were surprised to see a giant new plume (400 km high) over Tvashtar Catena (63 N) with UV color properties and a 1200-km diameter red plume deposit, both very similar to Pele. In the I31 flyby (August 2001) Galileo flew through the region occupied by the Tvashtar plume 7 months earlier. The images did not detect a plume, but SO2 may have been detected by the plasma science experiment. However, the images did reveal a giant (500 km high) new bright plume over the location of a new hot spot (41 N, 133 W) where no plume had been previously detected, and with a bright white plume deposit. The I31 images also revealed a new red ring (1000 km diameter) surrounding Dazhbog Patera (55N, 302 W). Surt, Aten, Tvashtar, and Dazhbog form a class of short-lived Pele-like plumes at high latitudes. High-resolution images have shown that plume vent regions include lava flows, lava lakes, and fissures, but we have yet to identify an actual vent structure.
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