The idea of a moon having its own moon sounds strange but fascinating. People often wonder if a smaller object could orbit around a regular moon, just like moons orbit planets. Scientists have actually studied this question for years, and while it’s possible in theory, it’s far more complicated in practice. Here’s what we know about whether moons can have their own moons and why we haven’t found one yet.
Moons orbit planets, not the Sun.
Before we talk about moons having moons, it helps to understand how moons work. A moon stays in orbit because the planet’s gravity is strong enough to keep it from floating away into space. That balance is what keeps everything moving smoothly. If a moon were to have another smaller moon, the planet’s pull would interfere with that smaller orbit. It would make it hard for the little moon to stay in one place for long.
Scientists call them “submoons.”
A moon orbiting another moon has a proper scientific name: it’s called a submoon. Researchers have run computer models to see if submoons could exist, and the results suggest it might be possible in rare cases. However, the conditions would have to be just right. The moon would need to be big enough, far enough from its planet, and stable enough to hold something in orbit around it.
Gravity makes things tricky.
Gravity from the nearby planet pulls strongly on both the moon and any smaller object trying to orbit it. The closer a moon is to its planet, the harder it is for a submoon to survive without being pulled away. This means most moons in our Solar System are too close to their planets for a smaller body to stay in place for very long. The planet’s gravity simply overpowers the moon’s own pull.
The size of the moon matters.
Only large moons could possibly have enough gravity to keep a submoon in orbit. Moons like Jupiter’s Ganymede or Saturn’s Titan are good examples because they’re almost as big as small planets. Even then, their parent planets’ gravity would make things unstable. So far, no submoon has ever been observed around any of them.
Computer models show it could happen briefly.
Simulations suggest that a submoon could orbit for a short time before being pulled away. It might last thousands or even millions of years, depending on distance and size, but it wouldn’t be permanent. Eventually, it would either crash into the larger moon, escape into space, or get captured by the planet itself.
Earth’s Moon doesn’t qualify.
Some people wonder if Earth’s Moon could have a tiny moon of its own, but it’s too close to Earth for that to work. Our planet’s gravity would pull the smaller object out of orbit within a short time. That’s why the Moon only hosts temporary visitors like passing asteroids that get caught for a few months before drifting away again.
The rules of orbit make it difficult.
For something to orbit steadily, it must move at the right speed and distance. If it’s too slow, it falls inward; if it’s too fast, it escapes into space. A submoon would need perfect balance to avoid both. Since moons orbit in a planet’s strong gravitational field, that balance is nearly impossible to achieve for long periods.
Tides can tear smaller objects apart.
Just as the Moon pulls Earth’s oceans to create tides, planets pull on their moons. These tidal forces stretch and squeeze objects in orbit. A small submoon would feel those forces even more intensely. As time goes on, those pulls could rip the smaller body apart or slowly drag it closer until it crashes into the larger moon’s surface.
Some exoplanets might make it possible.
In distant solar systems, things might work differently. If a large moon orbited far enough from its planet and had the right mass, it could possibly hold onto a small submoon for a while. So far, no one has spotted one, but telescopes are improving fast. It’s possible we’ll find one someday in another star system.
The idea still fascinates scientists.
Even though no confirmed submoon has been found, astronomers keep studying how they might exist. It helps us understand how gravity, orbits, and stability work across the universe. So, while a moon having its own moon isn’t happening in our Solar System right now, the science behind it continues to spark curiosity. It’s a reminder that space still holds plenty of mysteries waiting to be solved.