Io was discovered on January 8, 1610 by Galileo. This eventually lead to the understanding of moons and suns.
Io is one of the most colorful satellites in the galaxy and it has about 200 volcanoes. It is one of the most volcanically active moons in the solar system. When they were looking Io and saw what appeared to be a lump of some sorts, they thought it was another moon but then they realized oh that's a volcano shooting lava 150 miles high. Io is only slightly bigger then our moon.
Jupiter's moon Io: A Volcanic Inferno
BOOKS:Brewer, Duncan. Jupiter. New York: Marshall Cavendish, 1992. Print
VIDEOS: Jupiter's Moon Io: A Volcanic Inferno. Dir. Odalis Sanchez. 2013. Youtube.