Io, a moon of Jupiter. On June 11, 1979, using infrared photometry from the 2.2-m telescope on Mauna Kea, Hawaii, William Sinton observed what may have been an eruption from lo. Within the region on lo where Sinton believes the eruption may have occurred, a caldera was discovered on Voyager 2 imagery (early July) that was not present on imagery from Voyager 1 (early March). An earlier observation of what may also have been an eruption is described in Witteborn et al. .