Jupiter’s polar regions—anywhere between 10 and 30 times greater than any seen on Earth. Which they expected—everything’s bigger and badder on Jupiter. Trouble is, Jupiter’s aurora isn’t 10 or even 30 times stronger than Earth’s. It’s about a hundred times stronger. And there is no Earthly explanation for that discrepancy.

“Basically, the aurora is a factor of 10 brighter than it should be based on Earth-like physics,” Mauk says.

Whatever process accelerates Jupiter’s electrons up to a million electron volts is likely a total unknown. And Mauk, with the help of theorists and data from a few more orbits, is already on the trail of what that might be. “After orbit seven we saw what I would consider to be the smoking gun,” Mauk says. Mauk’s Jedi instrument saw the characteristic inverted V structure, but the electron excitement didn’t end there. As the electrical potential rose at the peak of the V, the acceleration went from coherent and linear to random—Mauk calls that a stochastic acceleration process. “Something goes unstable, and you start forming these waves,” Mauk says. “Some electrons gain a lot of energy, some just a little.”
What makes things get all unstable and random? Unclear.