Volcanic Activity on lo at the Time of the Ulysses Encounter
John R. Spencer 1,
Robert R. Howell 2,
Beth E. Clark 3,
David R. Klassen 2, and
Daniel O'Connor 4
1 Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001
2 University of Wyoming, Physics and Astronomy Department, Box 3905 University Station, Laramie, WY 82071
3 University of Hawaii, Planetary Geosciences Division, SOEST, 2525 Correa Road, Honolulu, HI 96822
4 University of Hawaii, Department of Physics and Astronomy, Honolulu, HI 96822
The population of heavy ions in lo's torus is ultimately derived from lo volcanism. Groundbased infrared observations of lo between October 1991 and March 1992, contemporaneous with the 8 February 1992 Ulysses observations of the lo torus, show that volcanic thermal emission was at the low end of the normal range at all lo longitudes during this period. In particular, the dominant hot spot Loki was quiescent. Resolved images show that there were at least four hot spots on lo's Jupiter-facing hemisphere, including Loki and a long-lived spot on the leading hemisphere (Kanehekili), of comparable 3.5-micrometer brightness but higher temperature.
Submitted on June 1, 1992
Accepted on August 3, 1992
