Our Moon May Not Be Able To Have Its Own Mini-Moon, But A Meteorite Recently Exploded On The Lunar Surface
When you realize that planets like Saturn have 60 moons, and Jupiter has 63, you have to wonder whether moons can have their own moons. Saturn’s satelite Titan is larger than the planet Mercury, so it’s not hard to imagine another rock circling it. Fraser Cain, publisher of Universe Today, one of my favorite space publications, tackled this question, and has dashed my hopes of discovering an infinite series of moons. It turns out that a moon can’t have a moon—unless some specific stuff is going on, which we’ll talk about later. At least the reasons this can’t happen are interesting, and that makes everything okay.
Apparently, “moon” has no explicit definition. If you look it up, you’ll find references to Earth’s Moon, but no official definition about what moons are in general. I thought science had this stuff nailed down. Moons do have some consistent attributes, though: they’re whole, sold objects that orbit around a bigger body, probably a planet, probably orbiting a star. Whatever the moon orbits is orbiting something else, etc. Technically, the Moon does have a moon, or at least something distinct orbiting it: NASA’s Lunar Reconnaissance Orbiter, which has been circling and photographing our Moon since 2009. But its lifespan is limited, and sheds light on why no moons in our Solar System can have their own satellites.