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NASA scientists have discovered new information on one of Jupiter's moons, indicating it has a molten magma sub-surface.

This discovery, made using data analysis from NASA's Galileo spacecraft, reveals why that particular moon is the most volcanic object known in the solar system. The moon, which is named Io, produces about 100 times more lava each year than all the volcanoes on Earth combined.

"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," Krishan Khurana, lead author of the study and former co-investigator on Galileo's magnetometer team at UCLA, said.

"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."

The difference Io and the volcanoes on earth is Io's volcanoes are distributed all over its surface. Volcanoes on earth are pretty localized to hotspots near the "Ring of Fire" in the Pacific Ocean. A global magma ocean about 30 to 50 kilometers (20 to 30 miles) beneath Io's surface explains the moon's activity.

"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," said Torrence Johnson, a former Galileo project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "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."

The moon's volcanoes were originally discovered in 1979 by NASA's Voyager spacecraft. The volcanoes on Io, made it the only known body in the solar system other than Earth known to have active magma volcanoes. Galileo has been orbiting Jupiter since 1995, and has been in the planet's atmosphere since 2003.

"During the final phase of the Galileo mission, models of the interaction between Io and Jupiter's immense magnetic field, which bathes the moon in charged particles, were not yet sophisticated enough for us to understand what was going on in Io's interior," Xianzhe Jia, a co-author of the study at the University of Michigan, said in a statement.

However, recent work in mineral physics made discovery of the new knowledge possible. The discovery found that a group of rocks known as "ultramafic" rocks become capable of carrying substantial electrical current when melted. These rocks form from the cooling of magma.

The discovery made scientists hypothesize that Io's strange signature was produced by current flowing in a molten or partially molten layer of this kind of rock. Tests confirmed this hypothesis, that the rocks detected by Galileo were forms of ultramafic rocks.

The research was conducted by scientists at the University of California, Los Angeles; the University of California, Santa Cruz;, and the University of Michigan, Ann Arbor.