Above Jupiter's poles, auroras blaze as electrons are accelerated by electric fields and slam into the upper atmosphere, making the gas glow. But not all electrons head downward. Some, it turns out, get a kick in the opposite direction — away from the planet, into deep space.
Juno, orbiting Jupiter, caught these "runaways" at distances from 13 to 50 planetary radii (Jupiter's radius is about 71,400 km). The JEDI instrument recorded electrons with energies from 30 to 1200 keV — hundreds of times more energetic than particles in a typical TV set. Narrow beams of such electrons were found throughout the surveyed region.
Comparing energy fluxes showed that the beams in the middle magnetosphere and the electrons accelerated above the poles are kin. Accounting for angular scattering (how particles "sway" along magnetic field lines) confirmed that the observed beams are indeed the same electrons that first accelerated at the pole and then flew off into the distance.
Thus, Jupiter's auroras are linked to streams of particles escaping into space. The same accelerator above the pole sends electrons both into the atmosphere and in the opposite direction — away from the planet.
Jupiter's magnetic field is 20,000 times stronger than Earth's, so its magnetosphere is enormous: its tail stretches beyond Saturn's orbit.