Sep 8, 2017

Jupiter's auroras are powerful —and very different from Earth's

Jupiter's southern aurora, captured in February by NASA 's Juno. (Credit: G. Randy Gladstone, SWRI)

Jupiter is home to the solar system's most powerful auroras. Their source is a mystery but researchers reported this week that they now know the planet's auroras are generated by processes different from those on Earth.

How it works on Earth: Auroras are created when the solar wind blows over the planet's magnetic fields and drives electrons into oxygen and nitrogen in the atmosphere. Those electrons then emit photons that the luckiest of us get to see as the vibrant colors of the Northern and Southern Lights.

How it works on Jupiter: It's different. The rotation of the planet in its own magnetic field, not the solar wind, can generate 400,000 volts of charge as it pushes electrons toward the atmosphere. But unlike on Earth, that doesn't create Jupiter's brightest auroras.

"We assumed the most intense auroras were created by these strong potentials that we expected to find. We've found them but they don't seem to be as important as we thought. Something else is stepping in," study author Barry Mauk from Johns Hopkins University Applied Physics Laboratory told Axios.

Best guess: As charged electrons in plasma gases above the planet's atmosphere interact with plasma waves, they gain or lose energy. Over time, Mauk says, in a random fashion, electrons at different energies may hit the atmosphere and cause auroras. These turbulent interactions happen on Earth, too, and create strong fluxes of energy down toward the atmosphere but a weak flux coming up. Mauk: "At Jupiter, for reasons we don't understand, even though the downward fluxes are strong enough to create most powerful aurora in the solar system, the upward fluxes are even stronger."

What's next: The orbit of Juno, the NASA spacecraft being used to study Jupiter, will soon pass closer to the aurora over the planet's northern pole. Mauk hopes that will tell them more about the processes at play.

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