Io: Ground-Based Observations of Hot Spots

Observations of Io in eclipse demonstrate conclusively that Io emits substantial amounts of radiation at 4.8 and 3.8 micrometers and a measurable amount at 2.2 micrometers. Color temperatures derived from the observations fit blackbody emission at 560 K. The required source area to yield the observed 4.8-micrometer flux is approximately 5 × 10^-5 of the disk of Io and is most likely comprised of small hot spots in the vicinity of the volcanoes.