How Many Moons Does Mercury Have?

by Fraser Cain on March 13, 2012

Does Mercury have a moon?

Since the Earth has a moon, and Saturn has more than 60, here’s a good question: does Mercury have moons? Unfortunately, the answer is no, Mercury has no moons.

But if moons are so common in the Solar System, and even Pluto, which is smaller than Mercury has moons, why doesn’t Mercury have moons?

The Earth got its moon when a Mars-sized object crashed into our planet, and the debris collected into the Moon. It’s possible that a similar impact happened to Mercury early on in its history. But the moon would have either drifted away or crashed back down onto the surface, because it’s not there anymore.

Mars got its two moons, Phobos and Deimos by capturing asteroids. This is more likely for Mars because it’s near the asteroid belt. There aren’t as many asteroids near Mercury as there are near Mars.

Finally, Pluto probably captured its moons smallest moons, Nix and Hydra, when they strayed to close. These moons are icy bodies that would behave like comets if they got too close to the Sun. They wouldn’t last long in the inner Solar System.

And so, the answer to the question: does Mercury have any moons… is no.

For a time in the early 1970s, astronomers thought the Mercury might have a moon. Instruments on board NASA’s Mariner 10 spacecraft detected large amounts of ultraviolet radiation that astronomers said, “had no right to be there”. And then the next day, that radiation disappeared. Some astronomers thought that this was radiation was coming from a moon. It was later discovered to be a more distant star.

We’ve written several articles for Universe Today about Mercury. Here’s an article about the gravity on Mercury, and here are some facts on Mercury.

If you’d like more info on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We’ve also recorded an episode of Astronomy Cast all about Mercury. Listen here, Episode 49: Mercury.


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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