Io, one of the four Jovian moons discovered by Italian astronomer Galileo Galilei in the early 17th century, orbits Jupiter so closely the giant planet's gravity places great stresses on the moon's crust.
Bruce Fegley Jr. at Washington University used new computer models of volcanic eruptions on Io to show the lavas are so hot there they are vaporizing sodium, potassium, silicon and iron -- and perhaps other materials -- and sending them boiling away high into the moon's atmosphere.
Fegley said he has found some of these elements are vaporized at least partly elementary gases, while others are boiled into different molecular forms, such as silicon monoxide, silicon dioxide and iron monoxide.
"The interesting thing about this is that astronomers have observed silicon monoxide in other environments in interstellar space," Fegley said, "most notably in the atmospheres of cool stars."
He said scientists will want to know how Io can maintain such high temperatures without becoming totally molten, and how does the moon manage to have a crust strong enough to support mountains that are larger than Mt. Everest.