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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.

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  • $\begingroup$ There is another factor in this - time scale. Aurorae are typically observed as variations in intensity by human observation over a very short period of time. Due to eccentricity of the orbits all planets will experience a fluctuation in the intensity of the solar wind, assuming constant output of the sun. A solar flare directly at a planet would increase the solar wind for an short period of time. $\endgroup$
    – MaxW
    Jan 22, 2017 at 5:02
  • $\begingroup$ Cosmic ray induced Aurorae inside your own head: en.wikipedia.org/wiki/Cosmic_ray_visual_phenomena $\endgroup$
    – Wayfaring Stranger
    Jan 24, 2017 at 17:26

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You may be interested to learn that Jupiter experiences aurora on its poles nearly (if not totally) non-stop. These aurora never cease, because they do not rely entirely on the sun as their source of charged particles, instead receiving particles from the volcanic ejections of its moon Io, as well as from cosmic rays. Granted, these aurora are occurring in the ultra-violet, but they are still 'noticeable'.

In short, yes aurora can be caused by non-solar sources, and conceivably cosmic rays at that. As to your other question concerning 'how much' of the aurora is due to which sources... I couldn't tell you how much of the auroras visibility comes from the sun, and I doubt there is much (or any) information on that subject, since determining the source of such convoluted light is likely outside the realms of both interest and empiricism. Perhaps you could pioneer that research? In any case, an intriguing subject to be sure.

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  • $\begingroup$ The Earth's aurora are nearly continuous as well and the particles that cause them come from the geomagnetic tail, not the solar wind or sun. The UV part of the aurora are more continuous and easier to observe from space than the visible (i.e., larger signal-to-noise ratio on night-side of Earth). $\endgroup$
    – honeste_vivere
    Jan 30, 2017 at 14:35

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