• Moonmoon: Also called submoon, or a moon orbiting a moon. New research details if and when one may exist
  • The planets orbit the Sun, while various moons orbit the planets themselves. Is it possible for a moon to have a satellite of its own? A new research paper has described the circumstances in which this might be possible, but what has caught the fancy of the scientific community — and Internet users — is what to call such a moon of a moon. In their paper on the preprint server, astronomers Juna Kollmeier and Sean Raymond have used the term “submoon”. Other scientists, however, have preferred “moonmoon”.
  • No moonmoon is known to exist in the Solar System. For one to exist, very special circumstances would need to be place. The host moon needs to have a sufficiently large mass, and the moonmoon must be sufficiently small. Distance too is crucial. The moonmoon needs to be close enough to the moon to be bound by its gravity — but not so close as to be torn apart by tidal forces — and both moons need to be far enough from the planet to prevent the moonmoon from being caught in the planet’s gravity, rather than the moon’s.

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