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R. R. Howell, J. L. Gregg, C. Crumrine (U. Wyoming), G. S. Orton, B. M. Fisher, J. G. Goguen (JPL)
During late May of 1998 one of the periodic brightenings of Loki began and as of 6 August was still continuing. During these brightenings, which seem to occur every couple years, the 5 micron flux from Loki reaches a level of 1/4 to 1/2 of that from the sunlit disk, and volcanic eruption rates may correspond to those inferred for terrestrial flood basalts. The 1998 brightening has been particularly well observed, with frequent near infrared eclipse and Io-Jupiter occultation measurements from the Wyoming Infrared Observatory as well as from other sites. Furthermore, during this period the Io-Jupiter occultation work was successfully extended to a wavelength of 10.3 microns, near the peak of the hot spot emission. This enables us to place constraints upon the total volume of material erupted and the total heat flow. A preliminary reduction of the observations, obtained 21 July using the MIRLIN camera at the IRTF, shows that roughly 2/3 of the total 10.3 micron in-eclipse flux comes from Loki, with the remainder distributed across the disk from what are presumably multiple faint hot spots. The frequent observations combined with the wide spectral coverage of this event will allow detailed tests of lava flow models. The beginning of the Loki brightening corresponded closely to the time of the Galileo E15 encounter and it has continued through the E16 encounter. Additional ground-based observations are planned for August and September.
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The author(s) of this abstract have provided an email address for comments about the abstract: rhowell@uwyo.edu