Aurorae are caused by energetic particles interacting with planetary atmospheres. Part of this flux comes from the Sun (solar wind) while the rest is cosmic radiation. My main question is: could a planetary body located far away from the Sun (or any other star), with a suitable atmosphere and magnetosphere, have noticeable* aurorae, just from being exposed to cosmic rays? A related question would be: do we know how much of the aurora is caused by the solar wind, and how much by cosmic rays? And thirdly: is there any other way that a planetary body could produce aurorae, such as its own electromagnetic emissions?
*I know "noticeable" doesn't really work as a limit, but for the time being, I'm talking of electromagnetic radiation that can be distinguished clearly from the background of a planet's disc using instruments not more advanced than our current telescopes at interplanetary distances.