There's a vast ocean of molten magma beneath the surface of Jupiter's moon Io, NASA scientists have found.
Io is the only body in the solar system, other than Earth, that's known to have active volcanoes. The energy for the volcanic activity comes from the squeezing and stretching of the moon by Jupiter's gravity.
"Scientists are excited we finally understand where Io's magma is coming from and have an explanation for some of the mysterious signatures we saw in some of the Galileo's magnetic field data," says Krishan Khurana, lead author of the study and former co-investigator on the Galileo spacecraft's magnetometer team at UCLA.
"It turns out Io was continually giving off a 'sounding signal' in Jupiter's rotating magnetic field that matched what would be expected from molten or partially molten rocks deep beneath the surface."
Io produces about 100 times more lava each year than all the volcanoes on Earth. While Earth's volcanoes occur in localized hotspots like the 'Ring of Fire' around the Pacific Ocean, Io's are distributed all over its surface.
A global magma ocean about 20 to 30 miles beneath Io's crust helps explain why.
"It has been suggested that both the Earth and its moon may have had similar magma oceans billions of years ago at the time of their formation, but they have long since cooled," says Torrence Johnson, a former Galileo project scientist based at NASA's Jet Propulsion Laboratory (JPL).
"Io's volcanism informs us how volcanoes work and provides a window in time to styles of volcanic activity that may have occurred on the Earth and moon during their earliest history."
Tests show that the signatures detected by Galileo are consistent with a rock such as lherzolite, an igneous rock rich in silicates of magnesium and iron. The magma ocean layer on Io appears to be more than 30 miles thick, making up at least 10 percent of the moon's mantle by volume. Its temperature is probably more than 2,200 degrees Fahrenheit.