A bevy of satellites buzzing around in the Earth's magnetosphere has found at least part of the answer to a long-standing puzzle about the source of the charged particles that feed the aurora.
The charged particles come from explosions on the sun and smash into the Earth's magnetic field, which repels the bulk of them. But many slip through, often via a physical process called magnetic reconnection, where the magnetic field traveling with the particles breaks and reconnects with the Earth's field, opening a window for the particles to surge through. Once inside, these excited particles can spiral down toward the poles and create brilliant auroras when they hit the atmosphere.