Transcript: Jupiter's Io has a highly elliptical orbit. While most satellites in the distant solar system should be cold, icy, and geologically dead, theorists speculated in the 1970s that tidal heating of Io could lead to volcanic activity. In 1979 the Voyager I space craft approached Jupiter after 18 months of travel and photographed a splotchy, yellow-orange surface with no craters, indicating it was geologically young. Over the next few years many active volcanoes were discovered on the surface of Io, and these were seen in motion shooting material up into the weak Io gravity where it would then fall lazily back to the surface. The dark hotspots on the surface were found through infrared techniques to have temperatures of 600 to 700 Kelvin, nearly 800 degrees Fahrenheit. Through its many volcanoes, 10 centimeters of sulfur and sulfur compounds are added to the surface of Io every year.