Planets orbit stars and moons orbit planets, but can another celestial object orbit around a moon? A new study suggests that, yes, it can happen.
Astronomers Juna Kollmeier of Carnegie Institution for Science and Sean Raymond of the Laboratoire d'Astrophysique de Bordeaux ran a computer simulation to predict whether natural satellites such as the Earth's Moon can have a natural satellite of its own.
The proof can now be viewed via the preprint site arXiv.org.
Moon Of A Moon
There are about 170 moons in the Solar System, most of which orbit the gas giants Jupiter and Saturn. Most moons are smaller than the planets they orbit, but some actually bigger than planets. Ganymede and Titan, in particular, are smaller than Jupiter and Saturn but are larger than the planet Mercury.
There are specific conditions for a moon to be able to capture its own moon. For one, a celestial object such as an asteroid or a comet should be close enough to the main moon in order to be captured by its gravity, but not close enough to be torn apart by a planet's tidal forces. There should also be enough distance between the main moon and the planet it orbits.
While a moon orbiting another moon does not exist within the Solar System, four moons meet the requirements: Callisto (Jupiter), Titus (Saturn), Iapetus (Saturn), and the Earth's own moon.
Moreover, a moon and its moon should be able to maintain their gravitational balance for a long period of time. Earth's moon, for example, is very slowly drifting away.
What Is In A Name
Kollmeier and Raymond dubbed a moon orbiting a moon a "submoon" in their study but as expected, the internet has better ideas. Apparently, submoon was outshined by the more delightful term "moonmoon" based on a popular meme.
Other terms being considered are "moonlet," "moonito," "moonette," "moonlet," "grandmoon," and "metamoon."
Finding Moonmoon In The Universe
So far, the existence of submoons has not been observed. While numerous exoplanets have been identified over the past couple of years, observing exomoons have been a challenge to scientists.
Earlier this month, a paper has, for the first time, found a moon located outside of the Solar System. It is said to be as big as Neptune and is orbiting a planet 8,000 light-years away from Earth. It would be doubly difficult to find a submoon orbiting an exomoon.