Jupiter's auroras arise from a magnetic 'tug-of-war' with volcanic eruptions on its moon Io

Jupiter's auroras are caused by a cosmic game of "tug-of-war," fueled by volcanoes on the planet's innermost moon, Io, new research suggests. 

NASA's Juno spacecraft and Hubble Space Telescope have revealed new evidence suggesting Jupiter's rapid rotation and the release of sulfur and oxygen from volcanoes on Io — the most volcanically active world in the solar system — create an electric current system that drives the powerful auroras observed around the gas giant's poles, according to a statement from the University of Leicester. 

"We've had theories linking these electric currents and Jupiter's powerful auroras for over two decades now, and it was so exciting to be able to finally test them by looking for this relationship in the data," Jonathan Nichols, lead author of the study from the University of Leicester, said in the statement. "When we plotted one against the other I nearly fell off my chair when I saw just how clear the connection is." 

Related: Juno's Amazing Views of Jupiter

Jupiter is more than 11 times wider than Earth, completing one rotation approximately every 9.5 hours. Orbiting Jupiter at an average distance of about 262,000 miles (422,000 kilometers), Jupiter's moon Io has more than 400 active volcanoes, which shoot lava dozens of miles high. These emissions fall into Jupiter's orbit and become electrically charged material, or plasma, according to the statement. 

Juno's Magnetic Field Investigation, which measures Jupiter's magnetic field from orbit, offers a detailed view of Jupiter's outer plasma environment and the electrical currents traveling through it, while Hubble's Imaging Spectrograph measures the brightness of Jupiter's auroras. 

"These exciting results on how Jupiter's aurorae work are a testament to the power of combining Earth-based observations from Hubble with Juno measurements," Scott Bolton, principal investigator for NASA's Juno mission, said in the statement. "The [Hubble Space Telescope] images provide the broad overview, while Juno investigates close up. Together they make a great team!"

Jupiter's rapid rotation repels most of the material ejected from lo, and as the material moves outward, its rotation rate slows. However, Jupiter attempts to keep this material spinning at its rotation speed via electric currents flowing through the planet's upper atmosphere and magnetosphere — the region dominated by the planet's magnetic field, according to the statement. 

In turn, this creates an electromagnetic tug-of-war between the electric current system and material in the magnetosphere. As the material travels along Jupiter's magnetic field lines, back toward the planet's poles, it cycles through the planet's upper atmosphere and interacts with gases, creating vivid aurora light shows. 

"It's thrilling to discover this relation because it not only helps us understand how Jupiter's magnetic field works, but also those of planets orbiting other stars, for which we have previously used the same theories, and now with renewed confidence," Nichols said in the statement. 

Their findings were published Jan. 5 in the Journal of Geophysical Research: Space Physics. 

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