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takyon writes:

If a Moon Has a Moon, Is Its Moon Called a Moonmoon?

A few years ago, an astronomer's son asked the type of question only kids and genius astrophysicists come up with: Can a moon have a moon? Juna Kollmeier of the Carnegie Institution Observatories couldn't answer her child's query, but she realized that investigating the idea could help answer questions about how moons form and even reveal some of the hidden history of the Solar System, reports Ryan F. Mandelbaum at Gizmodo.

The results, which she co-authored with astronomer Sean Raymond of the University of Bordeaux, were recently published in a short paper titled "Can Moons Have Moons?" on the preprint server arXiv.org, which hosts yet-to-be peer reviewed research. The study, however, has raised an even bigger question that now has the scientific Twitterverse riled up. Just what do you call the moon of a moon?

In their study, Kollmeier and Raymond looked at what would happen to a small submoon orbiting another moon. According to the paper, what they found is that in most cases there's just not enough space for a submoon to orbit another moon. Tidal forces would pull the little moon toward the host planet, ripping the mini moon to pieces.

For a submoon to survive, it needs to be small—about six miles in diameter or less. It also needs to orbit a large moon with enough gravity to hold it in place and must be far enough away from the host planet to complete its own orbit. It turns out that several moons in our own solar system fit the bill and could host submoons, including Titan and Iapetus, which orbit Saturn, and Callisto, which orbits Jupiter. Even our own moon is the right size and distance from Earth to potentially host its very own moon.

Subsatellite.

Also at ScienceAlert, Quartz, and Know Your Meme.

Original Submission