<p>Just add the prefix "exo-". At least exocomet and exomoon seem to be <a href="https://en.wikipedia.org/wiki/Exocomet" rel="nofollow">established</a>.</p>

CC BY-SA 3.0
2015-03-07T04:24:54.530Z
2015-03-07T04:24:54.530Z
LocalFluff
<p>I have to disagree with the accepted answer. The terms <em>Planets</em>, <em>moons</em>, <em>asteroids</em>, <em>planetesimals</em> are generic and are not implied to mean objects in the Solar system. So, these terms are completely correct when dealing with the generic objects.</p>

<p>When specifically emphasizing the fact that a certain objects is not in the Solar system, then you may want to add 'exo' for disambiguation, but this should be reserved for this purpose only.</p>

<p>A planet is a planet no matter where. Same with a house, which is a house no matter whether it's in your home town or elsewhere on the Earth.</p>

<hr>

<p>Note in edit: My answer is based on the practice among professional astronomers and not on what some dictionaries say. I reckon the latter are somewhat behind the times, when all planets, asteroids etc. known were those in orbiting the Sun. Wikipedia is a great resource, but <em>anybody</em> can change its contents and, not surprisingly, some of its pages are quite biased.</p>

CC BY-SA 4.0
2020-03-11T03:19:16.797Z
there's no longer an accepted answer
uhoh
CC BY-SA 3.0
2015-03-09T21:33:10.973Z
Wikipeia says, "asteroids are minor planets, especially those of the inner Solar System" and that "a minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor originally classified as a comet." According to this, asteroids need to orbit around the Sun.
Kelmikra
CC BY-SA 3.0
2015-03-09T23:26:57.243Z
@Kyth'Py1k: Perhaps that's just because all known asteroids are within the Solar System (unless I've missed some recent discovery). I have little doubt that if we discovered an asteroid-like (or planet-like) object orbiting, say, Alpha Centauri A, we'd call it an asteroid (or planet), Wikipedia notwithstanding.
Keith Thompson
CC BY-SA 3.0
2015-03-09T23:33:00.940Z
@KeithThompson Dictionary.com also [says](http://dictionary.reference.com/browse/asteroid) they must orbit around the sun, and Merriam Webster [says](http://www.merriam-webster.com/dictionary/asteroid) they need to be between Mars and Jupiter. Still, you could be correct.
Kelmikra
CC BY-SA 3.0
2015-03-10T10:23:35.737Z
@Kyth'Py1k it is often non-scientists who write the dictionaries and they cannot be expected to keep up with the pace of scientific discovery. The prefix exo is only used so the reader/listener can be under no doubt that you are talking about an object orbiting another star. [And as an aside, prefixing any statement with "Wikipedia says..." is a sure way to rile a scientist. Wikipedia is just a bunch of people, some knowledgeable, some not.]
ProfRob
CC BY-SA 3.0
2015-03-11T05:26:29.650Z
@Kyth'Py1k *"...nor originally classified as a comet"* Damn it! That excludes Ceres. The IAU should've hired a lawyer, someone who tries to apply math to language, before they tried to make their definitions of a *"direct orbit"* to no good place. An exo-thing is just a bump or discoloration in the light curve of a star, or at most it is a dot. Something we can't reach in a lifetime. But a non-exo planet/comet is something nearby at which we can throw things. Huge difference. "Exo" basically means out of this world. And we've seen stuff orbiting Saturn which kind of fulfills that criterium.
LocalFluff
CC BY-SA 4.0
2015-03-09T16:17:31.727Z
2020-03-14T17:04:10.867Z
2020-03-14T17:04:10.867Z
Walter
<p>Asteroids and comets only seem to refer to masses within the solar system, and it seems unclear whether planetesimal does. </p>

CC BY-SA 3.0
2015-03-08T09:45:03.543Z
With regard to planetesimals themselves, that is the right word. Google scholar found a paltry four articles that use either exoplanetesimal or exo-planetesimal. Compare that to the tens of thousands it found that just use planetesimal.
David Hammen
CC BY-SA 3.0
2015-03-08T13:41:17.610Z
@DavidHammen The problem with planetesimal is that it's ambiguous. Though it's sometimes defined as a small objects "whose internal strength is dominated by self-gravity and whose orbital dynamics is not significantly affected by gas drag," [other times](http://en.wikipedia.org/wiki/Planetesimal#Definition_of_planetesimal) its definition requires it's in the solar system and other times the name is only "applied to small bodies during the process of planet formation."
Kelmikra
<terminology>
What is the term for astronomical objects outside the solar system that are smaller than dwarf planets?
Kelmikra
# What is the term for astronomical objects outside the solar system that are smaller than dwarf planets?

(Asked by: username_0 on 2015-03-07)

Asteroids and comets only seem to refer to masses within the solar system, and it seems unclear whether planetesimal does.

**Tags:** terminology

> **Comments:**
> **username_1**: With regard to planetesimals themselves, that is the right word. Google scholar found a paltry four articles that use either exoplanetesimal or exo-planetesimal. Compare that to the tens of thousands it found that just use planetesimal.  
> **username_0**: @username_1 The problem with planetesimal is that it's ambiguous. Though it's sometimes defined as a small objects "whose internal strength is dominated by self-gravity and whose orbital dynamics is not significantly affected by gas drag," [other times](http://en.wikipedia.org/wiki/Planetesimal#Definition_of_planetesimal) its definition requires it's in the solar system and other times the name is only "applied to small bodies during the process of planet formation."  

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## 2 answers

### Answer by username_2 on 2015-03-07. Score: 4

Just add the prefix "exo-". At least exocomet and exomoon seem to be [established](https://en.wikipedia.org/wiki/Exocomet).


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### Answer by username_3 on 2015-03-09. Score: 3

I have to disagree with the accepted answer. The terms *Planets*, *moons*, *asteroids*, *planetesimals* are generic and are not implied to mean objects in the Solar system. So, these terms are completely correct when dealing with the generic objects.

When specifically emphasizing the fact that a certain objects is not in the Solar system, then you may want to add 'exo' for disambiguation, but this should be reserved for this purpose only.

A planet is a planet no matter where. Same with a house, which is a house no matter whether it's in your home town or elsewhere on the Earth.

---

Note in edit: My answer is based on the practice among professional astronomers and not on what some dictionaries say. I reckon the latter are somewhat behind the times, when all planets, asteroids etc. known were those in orbiting the Sun. Wikipedia is a great resource, but *anybody* can change its contents and, not surprisingly, some of its pages are quite biased.

> **Comments:**
> **username_0**: Wikipeia says, "asteroids are minor planets, especially those of the inner Solar System" and that "a minor planet is an astronomical object in direct orbit around the Sun that is neither a planet nor originally classified as a comet." According to this, asteroids need to orbit around the Sun.  
> **username_5**: @Kyth'Py1k: Perhaps that's just because all known asteroids are within the Solar System (unless I've missed some recent discovery). I have little doubt that if we discovered an asteroid-like (or planet-like) object orbiting, say, Alpha Centauri A, we'd call it an asteroid (or planet), Wikipedia notwithstanding.  
> **username_0**: @username_5 Dictionary.com also [says](http://dictionary.reference.com/browse/asteroid) they must orbit around the sun, and Merriam Webster [says](http://www.merriam-webster.com/dictionary/asteroid) they need to be between Mars and Jupiter. Still, you could be correct.  
> **username_6**: @Kyth'Py1k it is often non-scientists who write the dictionaries and they cannot be expected to keep up with the pace of scientific discovery. The prefix exo is only used so the reader/listener can be under no doubt that you are talking about an object orbiting another star. [And as an aside, prefixing any statement with "Wikipedia says..." is a sure way to rile a scientist. Wikipedia is just a bunch of people, some knowledgeable, some not.]  
> **username_2**: @Kyth'Py1k *"...nor originally classified as a comet"* Damn it! That excludes Ceres. The IAU should've hired a lawyer, someone who tries to apply math to language, before they tried to make their definitions of a *"direct orbit"* to no good place. An exo-thing is just a bump or discoloration in the light curve of a star, or at most it is a dot. Something we can't reach in a lifetime. But a non-exo planet/comet is something nearby at which we can throw things. Huge difference. "Exo" basically means out of this world. And we've seen stuff orbiting Saturn which kind of fulfills that criterium.  
> **username_4**: there's no longer an accepted answer  

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