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Guide to Non-Planets with Moons

Updated on August 20, 2013

Non-Planets with Moons

If it is not a planet, how can it have a moon? And there are two planets, Mercury and Venus, that do not have moons. So why bother to have a lens about this?

Well someone forgot to tell The Creator of the Universe that this is impossible because several worlds that are not one of the eight planets have moons.

The image is of Comet Hartley. I always thought that they were always round and spherical even when they out-gassed from heating by the Sun and left a tail in the solar wind. Obviously not.

Comet Tempel 1

Comets do not have moons -- that we know of. I threw this in just to raise the possibility.

near Earth object (136617) 1994 CC

near Earth object (153591) 2001 SN263 has two small moons but, that said, the moons are millions of tons. One is about one kilometer in diameter and the other is less than half a kilometer.

near Earth object (136617) 1994 CC also has two small moons but smaller by two orders of magnitude. They are about 50 meters (not kilometers, meters) in diameter and so they would be oddly shaped boulders. But the object these moons orbit may be spherical!

(136617) 1994 CC

go to the NASA link below and play the animation when you get there

'ELENIN' is THREE Objects (Maybe More)

Asteroid Discovery From 1980 - 2010

This is background information and not about moons.

This is a view of the solar system showing the locations of all the asteroids starting in 1980, as asteroids are discovered they are added to the map and highlighted white so you can pick out the new ones.

The final colour of an asteroids indicates how closely it comes to the inner solar system.

Earth Crossers are Red

Earth Approachers (Perihelion less than 1.3AU) are Yellow

All Others are Green

Could a Moon Have Moons?

Answer: No.

But since we humans share a characteristic with God of liking to do the impossible, stay tuned to the next module.

NASA Plans to Park Asteroid Around Moon

Remember what they just said about moons can't have moons? Scratch that. If the human race starts dragging troublesome asteroids away from collision courses with Earth and putting them into parking orbit around the moon so that mining companies can help themselves to free minerals, then the Moon will have moons.

Why passively watch as Wormwood or Nibiru smashes into the Earth and kills everyone when you can cash in and make trillions of dollars by mining it instead? By the way, NASA did not think of this first but I'm sure that they will take credit for the idea.

Can moons have moons?

Answer: Yes.


This is the biggest moon orbiting something other than a planet (Pluto was demoted) and it really orbits a center of gravity in space rather than Pluto.

Charon In Pluto's Sky

New Horizons - Charon Flyby

45 Eugenia

Photo Credit: Courtesy of Southwest Research Institute and National Science Foundation

Main Belt asteroid 45 Eugenia has two moons: Petit-Prince and S/2004 (45) 1.

You are mostly looking at square pixels because even with a probe passing through the Main Asteroid Belt and snapping a few pictures on the way to the outer Solar System, asteroids are so small that probes cannot image much better than telescopes on Earth or telescopes orbiting Earth. Size matters when the object is really small and hard to see.

45 Eugenia

There is a movie but no shattering conclusion or hero saving the day. Popcorn optional.

87 Sylvia

87 Sylvia has two moons: Romulus and Remus.

[Hey, isn't this the plot of Star Trek: Nemesis ?]

Just think, this moon is so tiny that it will probably never be colonized. But if it were,we would have Romulans right in our Solar System. Frankly, I would rather Vulcans or Q or Species 8472 than having as neighbors Romulans or Klingons or any culture obsessed with war and (like humans and science fiction fans) looking for villains. The Vulcans are uninterested in the stupidity of war. Any individual in the Q Continuum can make entire civilizations disappear with the snap of their fingers but refrain from doing so because the other Q would take away their god-like powers for abusing the less advanced (their version of Non-interference and Prime Directive). Species 8472 are good kissers according to Commander Chakotay. They don't put technology into their bodies like the Borg (that alone wins them points with me). But they use advanced technology. They just do not worship technology like us humans.


This is the moon of asteroid 243 Ida. Dactyl is "remarkably spherical" considering that the asteroid it orbits is not. In fact, only the four largest asteroids are recognized as dwarf minor planetoids. But all told, there are more than 1000 spherical bodies in the Solar System.


Vanth orbits Orcus and the fact that its color (red) differs greatly from Orcus (grey) complicates the effort to pin down its exact diameter. It is potentially the second largest minor moon after Charon.

Orcus was originally designated 2004 DW before it was given a name and Orcus is sometimes called "the anti-Pluto" because it stays on the opposite side of the sun from Pluto.

the moons of Haumea

The very name conjures images of Pacific beaches and palm trees in the breeze -- that would be swiftly destroyed by exposure to the actual climate there. This is because the terraformers have a real challenge here.

Haumea is a cubewano. That means that it is a classical Kuiper belt object. It has two moons. Hi'iaka (Haumea I) is 310 kilometers in diameter. Namaka (Haumea II) is 170 kilometers in diameter.

Cubewano is a term that astronomers came up with to screw with your head . . . okay, maybe I am confusing the word with that word bwana in the Tarzan movies. Or something. There are no hot tropical jungles out in the cold wastes of the outer outer Solar System. But it would be a hoot if somehow there were.

Consider this: Stationed right up in the Sun's face, Mercury's sunward side is blazing hot and yet Venus further away is hotter -- even on its night side !!! And there are places on Mercury that are among the coldest places in the Solar System because they never see sunlight. Then consider, Jupiter's moon Io which way out there has no business being hot and yet it is. Further out are cold moons like Enceladus (around Saturn) and Triton (around Neptune) which should be still and devoid of all activity but have ice volcanoes. Even comets wait until they get closer to the Sun than Saturn before they start outgassing and trailing tails of vapor and dust. So apparently these cold moons don't know that they are not supposed to have any activity. That's God for you, Always cramming the universe full of surprises. Like an oval-shaped world with two moons (Haumea).

Yes, Bwana.

Eris and Dysnomia

Eris is a Scattered Disc Object and the ninth most massive body known to orbit the Sun directly. It orbits beyond Neptune and beyond Pluto. This is the rascal that cost Pluto its status as a planet. After discovering that Eris was the first of many such dwarf planets, the choice was either to declare 1000 planets and force children to learn some mnemonic to remember all of them or to drop one and only have to learn eight planets. It was a no-brainer to demote Pluto. But the discovery of Eris precipitated this crisis in the definition of a planet.

Dysnomia orbits Eris. Its diameter is estimated to be between 350 and 490 kilometers.



One of Saturn's moons is known to have small companions at its L4 and L5 Lagrangian points. These companions are called Trojan moons, as their orbits are analogous to the Trojan asteroids of Jupiter. The Trojan moons are Telesto and Calypso, which are the leading and following companions of Tethys.

These companions however are moons of Saturn and _NOT_ of Tethys. So Telesto and Calypso are not moons of a moon.


Astronomers have not found moons of moons yet. The tidal effects of the primary tends to make such systems unstable. However, there is (another) Saturnine moon known to have small companions at its L4 and L5 Lagrangian points. These are called Trojan moons because their orbits are like the Trojan asteroids of Jupiter.

The Trojan moons here are Helene and Polysdueces, the leading and following companions of Dione.


Too bad that this is a false color image of Dione. It looks really cool. The purpose of the ultraviolet, green filter and infra-red photography is to show up Dione's geology.


Rhea's Rings

Saturn has more confirmed moons than Jupiter. The total number of moons both confirmed and unconfirmed is sixty-two. If you count the round chunks of rocks and ice in Saturn's rings, then the total number of moonlets is in the trillions. Applying this logic to Rhea, one of the moons of Saturn, we are confronted with an interesting problem of census or inventory. Rhea seems to have a ring.

However, if we apply common sense and look for the largest spherical object orbiting Rhea, then we might find the Solar System's first natural moon of a moon. It would also be the only known moon of a moon in the known universe. Therefore, even as a hypothetical, it is a fascinating question. [And a headache for astronomers whose duty is to define what is a planet and what is a moon.] The search is on.

Amazon Spotlight Personal Review

This hard cover book starts with Mars and works outward with concise information about all the Solar System's moons.

Solar System Moons: Discovery and Mythology
Solar System Moons: Discovery and Mythology

Mercury and Venus do not have moons and Earth only has one and creatures on Earth have been staring at it for millions of years. It is reasonable that some of us want a change of view. So this book comes along to fill the gap with knowledge about other moons in other skies.


Amazon Spotlight Personal Review

This paperback uses the first half of the book to talk about Luna, Earth's moon.

Moons of the Solar System: An Illustrated Encyclopedia
Moons of the Solar System: An Illustrated Encyclopedia

However, I recommend this book anyway because it is well illustrated and has several good appendices.


Astronomy questions from kids, Part 2

Question #6 --

Can a moon have a moon?



Alberto ECJ.  This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
Alberto ECJ. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

Can a moon have a moon?

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Wear your 3-D glasses.



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