If you gaze up at the night sky there’s a good chance you’ll spot Earth’s only large natural satellite. We just called it “the Moon,” but other planets have moons too. Recently, the first evidence of an exomoon — that is, a moon orbiting a planet in another star system — was revealed, but what if we found a planet with a moon that had a moon of its own?
This entirely speculative scenario has captured the interest of several astronomers who have taken it upon themselves to come up with their own terminology to describe these as-of-yet-undiscovered objects. The best (or worst?) name candidate thus far is so silly that it’s already taken the internet by storm: Moon-moons.
As ScienceAlert explains, all the discussion regarding moons existing around other moons has spun off of a pair of papers that are currently awaiting publication. The first is the work of astrophysicist Duncan Forgan who took the time to calculate whether or not the recently-researched exomoon candidate around the exoplanet Kepler-1625b could potentially be habitable.
In the paper, Forgan explains that while current observations of the potential exomoon suggest it wouldn’t reside within the star’s habitable zone. However, if the large, Neptune-sized moon had a moon of its own, and if that moon was a rocky body like Earth, it could have been habitable when Kepler-1625 was in its main sequence long ago.
That’s where we get to the heart of the issue. As Forgan describes the potential of a moon around another moon he uses the term “moon-moon.” It’s a silly term to begin with, but Moon Moon also happens to be the hook of a meme that gained popularity back in 2013. The gag was the result of one of those terrible “What’s your ______ name?” posts that attempts to give you a new nicknamed based on the first letters of your first and last name. In this particular case, the individual’s “Werewolf Name” ended up being Moon Moon.
Internet culture aside, the research is pretty interesting, and a paper that surfaced a few days later attempts to answer the question of whether a moon could even exist around another moon in the first place. Avoiding the term “moon moon” entirely — authors Juna Kollmeier and Sean Raymond prefer “submoon” instead — the scientists describe how it might actually be possible. Both papers are worth a read, but we’ll have to wait and see what term the astronomy community decides to go with.