# Is there a word for an object orbiting a brown dwarf?

In my answer to this question someone posed somewhere:

If an Earth-massed moon orbits a planet that has 74-83 times Jupiter’s mass, would the Earth massed moon still be a moon, or a planet?

I wrote:

A planetary mass object is an object with a mass large enough to be gravitationally rounded and less than about 13 times the mass of Jupiter or about 4,131.4 times the mass of Earth.

A planet is an object orbiting a star and having a mass in the range of a planetary mass object - large enough to be gravitationally rounded and less than about 13 times the mass of Jupiter or about 4,131.4 times the mass of Earth.

An object which orbits around a planet is called a natural satellite or a moon.

A brown dwarf is an object with a mass of at least about 13 times the mass of Jupiter or about 4,131.4 times the mass of Earth and less than about 75 times the mass of Jupiter or about 23,835 times the mass of Earth.

A star is an object with a mass at least about 75 times the mass of Jupiter or about 23,835 times the mass of Earth, and less than a few hundred times the mass of the Sun.

An object which orbits around a star and has a mass large enough to be gravitationally rounded and less than about 13 times the mass of Jupiter or about 4,131.4 times the mass of Earth is a planet.

An object which has a mass of 74–83 times Jupiter’s mass is not a planet. By definition it is near the dividing mass between brown dwarfs and low mass stars. So since by definition the Earth-massed object in the question is not orbiting a planet but either a brown dwarf or a star, it must not be classified as a moon orbiting a planet but must be classified as an object orbiting a brown dwarf or a star.

The word for a planetary mass object orbiting a star is planet.

And so far as I know there is no word for an object orbiting a brown dwarf, which is illogical as long as brown dwarfs are considered to be objects different from planets and from stars.

There should be a word for objects orbiting brown dwarfs. Like planoon or moonet or ooabd (object orbiting a brown dwarf) or nsoabd (natural satellite of a brown dwarf) or something.

So is there an astronomical word for objects that orbit brown dwarfs?

• Does it matter? Commented Feb 20 at 17:03
• Brown dwarfs are technically closer to stars than planets. So a qualifying object orbiting one would still be a considered planet. Commented Feb 20 at 18:06
• Something is off with your link above. The browser doesn't recognize it as a link to a different webpage. Commented Feb 21 at 7:35
• You copied the text of your link into the URL field instead of the actual URL you meant to link to. Commented Feb 21 at 7:55
• The only Google result for that specific "question" is a Reddit post which had its content [removed], and there's no trace of any comment resembling OP's answer. No trace of such a question in Astronomy.SE for sure, unless it's been deleted. I've edited the question to remove the link. OP may of course edit again to provide the actual link, or leave it like that. Commented Feb 21 at 12:46

In the question IAU 2018 Exoplanet definition the IAU's definition of an exoplanet is given which includes objects around brown dwarfs.

So the answer to your question is that a planetary-mass object orbiting a brown dwarf is called a planet.

That being said, all the exoplanet catalogs include objects with masses above 13 Jupiter masses. In other words low-mass brown dwarfs are counted as planets by the exoplanet catalogs if they orbit a star. So if they are counted as planets then they would presumably be orbited by moons. So the satellites of brown dwarfs that orbit stars could be called either moons or planets depending on whether you go by the exoplanet catalogs or by the IAU definition.

• "The IAU defines that a planet in the Solar System must orbit around the Sun, has enough mass to assume hydrostatic equilibrium, and has "cleared its neighborhood". There is currently no accepted definition for exoplanets." en.wikipedia.org/wiki/List_of_planet_types Commented Feb 23 at 1:41
• @Mazura thanks for pointing out a wikipedia article that needed to be updated.
– sno
Commented Feb 23 at 11:36
• @sno My favorite reply is "It must be correct, I wrote it only yesterday!" Commented Feb 23 at 18:48
• There are some high uncertainties in masses of exoplanets. I would like to think that this is the reason for some exoplanets being catalogued at greater than 13 Jupiter masses. Otherwise all brown dwarfs in binaries would be called planets. The problem is also, I think, that brown dwarfs are sort of stars that become planets. We humans love to categorize and name things and sometimes it comes back to bite us Commented Mar 3 at 15:03
• @JackR.Woods Well the NASA exoplanet archive includes objects with minimum masses up to 30 Jupiter masses and the Encyclopaedia of exoplanetary systems is up to 60 Jupiter masses and that's minimum masses, so there's more going on than just high uncertainties.
– sno
Commented Mar 3 at 21:38

You could always call them satellites.

A satellite is an object in space that orbits or circles around a larger entity.

To avoid confusion with artificial satellites, the term natural satellite is also preferable.

References:

• You could back up your answer with this article from JPL: Planetary Satellites of the Solar System. Commented Feb 23 at 11:51
• @AndrewMorton I had actually added a NASA K4 article as reference, but then I thought it was generally understood. I guess everyone knows it but don't use the same terminology ever. Commented Feb 23 at 12:03
• @BlacklightMG Yeah, what is considered "appropriate" terminology is often subjective and sometimes controversial within the realm of astronomy, especially when there is no clearly defined meaning. Though I'd say that considering such objects "natural satellites" is a fair assessment. Commented Feb 26 at 19:47