Science Gazette

Jupiter’s upper atmosphere is lit up by electromagnetic tug-of-war, according to Juno and Hubble data

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Using data from NASA’s Juno spacecraft and the Hubble Space Telescope, new Leicester space research has shown for the first time that a complex ‘tug-of-war’ lights up aurorae in Jupiter’s upper atmosphere.

The delicate current cycle produced by Jupiter’s fast rotation and the discharge of sulphur and oxygen from volcanoes on its moon, Io, is described in the research, which was published in the Journal of Geophysical Research: Space Physics.

Data from Juno’s Magnetic Field Investigation (MAG), which measures Jupiter’s magnetic field from orbit around the gas giant, and observations from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph were used by researchers from the University of Leicester’s School of Physics and Astronomy.

Their findings give the best evidence yet that Jupiter’s intense aurorae are linked to an electric current system that tugs at material in the planet’s magnetosphere, which is controlled by the planet’s massive magnetic field.

Dr. Jonathan Nichols is a corresponding author for the paper and a Reader in Planetary Auroras at the University of Leicester. He said, ”

“For over two decades, we’ve had ideas tying these electric currents to Jupiter’s tremendous auroras, and it was thrilling to be able to finally verify them by searching for this connection in the data.” When we plotted one against the other, I almost fell out of my chair when I realized how obvious the link is.

“It’s fascinating to find this relationship because it not only helps us understand how Jupiter’s magnetic field works, but also how the magnetic fields of planets circling other stars function, for which we’ve previously utilized the same ideas with increased confidence.”

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Jupiter spins once every nine and a half hours, despite its enormous size (it has a diameter more than 11 times that of Earth).

Io is the same size and mass as Earth’s moon, although it circles Jupiter at a distance of 422,000 kilometers, or around 10% farther away. Io is the most geologically active object in the Solar System, with over 400 active volcanoes.

Scientists have hypothesized a link between Jupiter’s aurorae and the material blasted from Io at a rate of hundreds of kilos per second for a long time, but Juno’s data was equivocal.

The Juno mission’s Principal Investigator (PI) is Dr. Scott Bolton of NASA’s Jet Propulsion Laboratory (JPL). He said, ”

“The power of integrating Earth-based Hubble views with Juno measurements is shown by these interesting insights on how Jupiter’s aurorae function.” The HST photos provide a general perspective, whereas Juno focuses on the details. They form an excellent team!”

The planet’s fast revolving magnetic field propels most of the material discharged from Io out from Jupiter, and as it goes outward, its rotation rate slows. Jupiter seeks to maintain this material spinning at its rotation speed through a system of electric currents running through the planet’s upper atmosphere and magnetosphere, resulting in an electromagnetic tug-of-war.

Jupiter’s major auroral emission was assumed to be driven by a component of the electric current flowing out of the planet’s atmosphere, transported by electrons shot downward along magnetic field lines into the upper atmosphere.

Prior to Juno’s arrival, however, this theory had never been tested since no spacecraft with suitable equipment had ever orbited Jupiter near enough. And, although such signs have subsequently been discovered, one of the major discoveries of Juno’s mission has been to reveal that the nature of the electrons above Jupiter’s polar regions is much more complicated than was originally predicted.

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During the early phase of Juno’s mission, the researchers contrasted the brightness of Jupiter’s major auroral emission with contemporaneous measurements of the electric current flowing away from the Solar System’s biggest planet in the magnetosphere.

Instruments on board the Hubble Space Telescope in Earth orbit witnessed these aurorae. The scientists proved the association between auroral intensity and magnetospheric current strength by comparing dawn-side current data with the brightness of Jupiter’s aurorae.

Stan Cowley, Emeritus Professor of Solar-Planetary Physics at the University of Leicester and study co-author, has spent the last 25 years studying Jupiter’s powerful aurorae. Professor Cowley continued, ”

“We now have the material to look in detail at the overall physics of Jupiter’s outer plasma environment, thanks to more than five years of in-orbit data from the Juno spacecraft, combined with auroral imaging data from the HST, and more is on the way from Juno’s extended mission, which is currently underway.” We expect that our current publication will be followed by many others that explore this rich source of fresh scientific knowledge.”

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