# Could a moon have a moon of its own? **URL:** \ **Category:** Factual Questions\ **Created:** [April 30, 2022, 12:16pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716 "2022-04-30T12:16:21Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Peter\_Morris](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/peter_morris/32/359_2.png) [@Peter\_Morris](https://boards.straightdope.com/u/Peter_Morris)\ **Post date:** [April 30, 2022, 12:16pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/1 "2022-04-30T12:16:21Z")
I think there are no examples in our own Solar System. But suppose we imagine a Jupiter-like gas giant orbiting a faraway star. This has several moons, including an Earth-like ball. Could there be a Luna-like rock orbiting? Is there any reason why it couldn’t happen? Maybe the gravity of the main planet would prevent a stable orbit forming, or something. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [April 30, 2022, 12:28pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/2 "2022-04-30T12:28:31Z")
Others more orbitally mechanically inclined will soon chime in, but I believe the answer is yes, but the choice of orbits that work for this is somewhat limited so would be more rare. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [April 30, 2022, 12:49pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/3 "2022-04-30T12:49:53Z")
[Paper](https://arxiv.org/pdf/1810.03304.pdf) says Titan, Iapetus, Callisto, Earth’s Moon, and Kepler-1625b-I could do it, in theory. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [April 30, 2022, 1:32pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/4 "2022-04-30T13:32:38Z")
Not exactly what you were probably thinking of, but: Pluto’s (not a planet anymore, I know) moon Charon orbits Pluto in such a way that their joint centre of gravity is outside Pluto. In other words, the two planets orbit each other as a double planet system, and Pluto is just as much a moon of Charon as Charon is Pluto’s. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 30, 2022, 1:45pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/5 "2022-04-30T13:45:18Z")
Can a thread have a thread of its own? > [@Is lt possible for the Earth to have a second Luna sized moon?](https://boards.straightdope.com/t/is-lt-possible-for-the-earth-to-have-a-second-luna-sized-moon/953830): > > …or would such a system be too unstable to last? Covers a little of the “multiple moons” physics. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [April 30, 2022, 1:49pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/6 "2022-04-30T13:49:43Z")
> [@Peter\_Morris](#): > > Is there any reason why it couldn’t happen? Our moon orbits the Earth which orbits the sun. So obviously you can have a three body system with that configuration. A fourth body would complicate the problem, but theoretically our Solar System could be orbiting a large black hole so we may already be in a 4 body configuration. ---
**Author:** ![EnolaStraight](https://avatars.discourse-cdn.com/v4/letter/e/41988e/32.png) [@EnolaStraight](https://boards.straightdope.com/u/EnolaStraight)\ **Post date:** [April 30, 2022, 1:53pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/7 "2022-04-30T13:53:35Z")
I asked this very question on the old boards about 20 years ago. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [April 30, 2022, 5:44pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/8 "2022-04-30T17:44:04Z")
Nothing theoretical about it. The entire galaxy is orbiting a central black hole. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 30, 2022, 6:16pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/9 "2022-04-30T18:16:47Z")
> [@beowulff](#): > > The entire galaxy is orbiting a central black hole. Not really. We are going around it, but it is not its gravity that holds us in orbit. If you removed the central black hole of the Milky Way, very little would change. Anyway, to the OP, a very qualified yes. You _can_ have a setup where a very large planet orbits a star, and a large moon orbits that planet, and a small object orbits that moon. It’s all about [Hill spheres](https://en.wikipedia.org/wiki/Hill_sphere). But, it would be very unlikely to develop on its own, and it would be very unstable and unlikely to last long, cosmologically speaking. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [April 30, 2022, 8:42pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/10 "2022-04-30T20:42:59Z")
Do we have satellites orbiting our own moon? If so is it difficult for them maintain an orbit? Like more difficult than the ones we have orbiting the earth. ---
**Author:** ![k9bfriender](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/k9bfriender/32/3283_2.png) [@k9bfriender](https://boards.straightdope.com/u/k9bfriender)\ **Post date:** [April 30, 2022, 8:55pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/11 "2022-04-30T20:55:48Z")
> [@Si\_Amigo](#): > > Do we have satellites orbiting our own moon? Yes, a few. > [@Si\_Amigo](#): > > If so is it difficult for them maintain an orbit? A little. Most require some level of station keeping. There really are no “permanent” orbits. > [@Si\_Amigo](#): > > Like more difficult than the ones we have orbiting the earth. A satellite in Earth’s geostationary orbit will orbit for millions of years easy. I don’t think that you could find an orbit around the moon that would persist for hundreds, much less thousands of years. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [April 30, 2022, 9:15pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/12 "2022-04-30T21:15:58Z")
> [@Si\_Amigo](#): > > Do we have satellites orbiting our own moon? If so is it difficult for them maintain an orbit? Yes we do and yes it is. But difficult because of [mascons](https://en.wikipedia.org/wiki/Mass_concentration_(astronomy)). ---
**Author:** ![DrDeth](https://avatars.discourse-cdn.com/v4/letter/d/b487fb/32.png) [@DrDeth](https://boards.straightdope.com/u/DrDeth)\ **Post date:** [April 30, 2022, 10:11pm UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/13 "2022-04-30T22:11:27Z")
You have to define “moon”. I have little doubt that some baseball sized rocks are orbiting various major moons in our solar system. But I think the OP is talking about a moon that would be visible from the surface, This would be difficult to have stable over a long term I think. ---
**Author:** ![Revtim](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/revtim/32/1042_2.png) [@Revtim](https://boards.straightdope.com/u/Revtim)\ **Post date:** [May 1, 2022, 3:20am UTC](https://boards.straightdope.com/t/could-a-moon-have-a-moon-of-its-own/963716/14 "2022-05-01T03:20:25Z")
I happened to recently read that the term for such a thing is a “moonmoon”. > **[Definition of moonmoon | New Word Suggestion | Collins Dictionary](https://www.collinsdictionary.com/us/submission/20495/moonmoon)** > > Definition of moonmoon | New Word Suggestion | Collins Dictionary