Magnetic reconnection near the planet as a possible driver of Jupiter’s mysterious polar auroras

Auroral emissions have been extensively observed at the Earth, Jupiter, and Saturn. These planets all have appreciable atmospheres and strong magnetic fields, and their auroras predominantly originate from a region encircling each magnetic pole. However, Jupiter’s auroras poleward of these “main” emissions are brighter and more dynamic, and the drivers responsible for much of these mysterious polar auroras have eluded identification to date. We propose that part of the solution may stem from Jupiter’s stronger magnetic field. We model large-scale Alfvénic perturbations propagating through the polar magnetosphere toward Jupiter, showing that the resulting <0.1° deflections of the magnetic field closest to the planet could trigger magnetic reconnection as near as ∼0.2 Jupiter radii above the cloud tops. At Earth and Saturn this physics should be negligible, but reconnection electric field strengths above Jupiter’s poles can approach ∼1 V m−1, typical of the solar corona. We suggest this near-planet reconnection could generate beams of high-energy electrons capable of explaining some of Jupiter’s polar auroras.

Plain Language Summary

When energetic particles from space hit a planet’s upper atmosphere the resulting chemistry can produce light, leading to spectacular “auroras.” Jupiter is the largest planet in the Solar System, with the strongest magnetic field generated in its interior, and with the brightest auroras. We understand why Jupiter’s auroras are so bright to a large extent, but a long-standing mystery is what causes the swirling auroras around Jupiter’s poles, which we do not see at other planets. We present a new idea that might lead to a solution to this problem. We show that under certain conditions in space just above Jupiter’s polar atmosphere some of the energy stored in the planet’s magnetic field can be released, possibly accelerating particles and producing auroras below. If this idea is supported by future research it would imply that Jupiter’s bright polar auroras are due to the planet’s very strong magnetic field, with implications for similarly strongly magnetized planets in orbit around distant stars.