A spacecraft enters an unnamed system and spotted a gas giant with a pulsating planetary ring, it glows bright intermittently. What natural phenomenon could be responsible for such brilliant display? It would be better if you can explain why the glows only occurs within certain range of the electromagnetic spectrum.

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    $\begingroup$ It may be worth noting (and maybe not) that this could vary based on whether you mean pulsating or scintillating. Not that I doubt that you said what you meant, just wanted to mention that in case scintillating was closer to the description (which could indicate volumes of gasses around parts of the rings that reflect light and travel). $\endgroup$ Mar 1, 2019 at 16:54

1 Answer 1


Io and Jupiter have a very special relationship. Io is a volcanic moon, which ejects charged particles. Due to its relatively low gravity (~0.18g), the particles escape, but they get trapped by Jupiter's immensely powerful magnetic field and form a plasma torus. The density of the plasma is higher close to and ahead of Io.

Jupiter and Io

Saturn is like a smaller Jupiter, but with huge rings. It has shepherd moons - moons that orbit between rings.

Now combine both: a gas giant with saturnian rings, a volcanic shepherd moon and a jovian magnetic field. The plasma shines (in specific wavelengths, even!), and the glow is reflected by the rings. The plasma glows and dims as the moon orbits the planet - it seems stronger when the moon is on the same side of the planet as you, and diminishes when the moon is on the other side.

For reference, the orbital periods of Prometheus and Epimetheus, two of Saturn's shepherd moons, are approximately 0.6 and 0.7 Earth days, respectively.

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    $\begingroup$ 👍You managed to find real world example! $\endgroup$
    – user6760
    Mar 1, 2019 at 11:57

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