Io, satellite of Jupiter, is the most volcanically active and hottest body in the solar system.The hottest spot in the solar system is neither Mercury, Venus, nor St. Louis in the summer. Io, one of the four satellites that the Italian astronomer Galileo discovered orbiting Jupiter almost 400 years ago, takes that prize. The Voyager spacecraft discovered volcanic activity on Io over 20 years ago and subsequent observations show that Io is the most volcanically active body in the solar system. The Galileo spacecraft, named in honor of the astronomer Galileo, found volcanic hot spots with temperatures as high as 2,910 Fahrenheit (1,610 Celsius). Now computer models of volcanic eruptions on Io performed by researchers at Washington University in St. Louis show that the lavas are so hot that they are vaporizing sodium, potassium, silicon and iron and probably other gases as well into its atmosphere.