This article got me thinking, can a planet hold a moon in orbit if it is just floating in the galaxy by itself not as part of a star system? Can a celestial body even qualify as a planet if it is floating around by itself?
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2$\begingroup$ Anything can orbit anything. This is just a mass question. $\endgroup$– Rory AlsopDec 23, 2013 at 18:41
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2$\begingroup$ @RoryAlsop Not even, you're such a hopeless traditionalist! :) :P $\endgroup$– TildalWaveDec 23, 2013 at 19:07
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$\begingroup$ @TidalWave this is extremely interesting, I too was a traditionalist until now $\endgroup$– Eduardo SerraDec 23, 2013 at 19:41
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1 Answer
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The answer is Yes.. Planets that don't orbit around a star are known as Rogue Planets. There is nothing preventing a rogue planet from having one or many moons.
Not so long ago, the first candidate for a free-floating exoplanet-exomoon system was presented in this paper. It looks like a gas giant several times larger than Jupiter with a sub-Earth mass moon.
Another study calculated and simulated scenarios where planets where ejected from their orbits around a star and concluded that around five percent of Earth-sized planets who are accompanied by Moon-sized natural satellites would retain them after the event.
