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For the first time ever, NASA's Juno spacecraft has spotted electrons being fired down into Jupiter's atmosphere at up to 400,000 volts. That's an enormous amount of energy that gives rise to the planet's glowing auroras. These incredibly high voltages, however, are only spotted occasionally — and that's raising questions about what exactly is behind some of the planet's most vivid glows at the poles.

The discovery, detailed in a study published today in Nature, was made possible by the instruments on board Juno, which has been orbiting Jupiter for a little over a year, passing by the poles closer than any other spacecraft has before. It confirms, in part, what astronomers expected, but it also shows that Jupiter's auroras behave differently than auroras on Earth — through processes that we don't fully understand yet.

Auroras, on both Earth and Jupiter, are formed when charged particles like electrons spiral down a planet's magnetic field lines, entering the atmosphere and creating a glow. On Earth, the most intense auroras are caused by solar storms, which occur when high-energy particles ejected from the Sun rain down on our planet. When these particles enter the atmosphere, they interact with gases and make the sky glow red, green, and blue at the poles. On Jupiter, auroras are formed by particles ejected mostly from the Io, the planet's moon. Io's volcanoes spew huge amounts of sulfur and oxygen into space, loading Jupiter's magnetic field with particles.

[...] "We've never flown right over the poles of Jupiter before," says Jonathan Nichols, a professor in the Department of Physics and Astronomy at the University of Leicester, who did not take part in the study. "So Juno is telling us about those particles for the first time."

https://www.theverge.com/2017/9/6/16256926/nasa-juno-jupiter-auroras-electrons

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