Moons which have other moons in orbit haven’t been found in our solar system, and researchers are now trying to look for this phenomena in other solar systems as well. Even though asteroids with moons have been found, scientists at NASA say that it’s very hard for moons to have their own moons.

Seth Shostak from the SETI Institute says that this is unlikely to happen because moons have little chance of dominating the gravitational force of the parent planet.

Webster Cash from the University of Colorado Center for Astrophysics and Space astronomy says that even if it’s possible for moons to have other moons in orbit, this wouldn’t last for long because the gravitational field from the parent planet would eventually destabilize the orbit of the moon’s moon, pulling it out of orbit.

Finding a moon which can handle its own moon would be one of NASA’s biggest achievements.