<p><a href="https://en.wikipedia.org/wiki/Earnshaw%27s_theorem" rel="nofollow noreferrer">Earnshaw's Theorem</a> tells us that it is impossible for a stationary mass to float in a stable gravitational equilibrium, so there is no configuration of exoplanets or moons that could levitate land islands above a planet.</p>
<p>Levitating islands have been discussed in several Worldbuilding Stack Exchange questions:</p>
<ul>
<li><a href="https://worldbuilding.stackexchange.com/q/33513/98864">Can airborne floating/flying islands be scientifically possible?</a></li>
<li><a href="https://worldbuilding.stackexchange.com/q/155959/98864">Can a planets magnetic field be strong enough to make floating continents?</a></li>
<li><a href="https://worldbuilding.stackexchange.com/q/143152/98864">Can the Meissner effect explain very large floating structures?</a></li>
</ul>
<p>The <a href="https://james-camerons-avatar.fandom.com/wiki/Unobtanium" rel="nofollow noreferrer">&quot;official&quot; explanation</a> for the floating islands in <a href="https://en.wikipedia.org/wiki/Avatar_(2009_film)" rel="nofollow noreferrer">Avatar</a> is that are largely composed <a href="https://en.wikipedia.org/wiki/Unobtainium#Science_fiction" rel="nofollow noreferrer">unobtainium</a>, a fictional room-temperature superconductor which levitates due to <a href="https://en.wikipedia.org/wiki/Flux_pinning" rel="nofollow noreferrer">flux-pinning</a> in Pandora's magnetic field.
This explanation is implausible but not impossible.
A <a href="https://www.ted.com/talks/boaz_almog_the_levitating_superconductor?language=en" rel="nofollow noreferrer">well-known video</a> reports a lift-to-weight ratio of 70,000 for a superconducting disk in a strong magnetic field gradient, so only a small fraction of unobtainium in the islands might be enough to levitate them in lesser magnetic fields. There are lots of very challenging issues about how the islands could have be initially formed with the flux pinned, and how stable the pinned flux is over geological time, but the idea is perhaps less ridiculous than I initially thought.</p>

CC BY-SA 4.0
2023-08-01T21:29:46.483Z
2023-08-01T21:29:46.483Z
David Bailey
<p>According to relativity gravity is a change in the geometry of space caused by mass. There are other theories of gravity in which gravity is a force.   And in some of those theories, it might be possible to produce negative gravity.  So possibly sky islands could be lifted up by anti gravity generators.</p>
<p>Otherwise artificial floating islands would be limited to something like fuller's cloud nine concept. <a href="https://science.howstuffworks.com/engineering/architecture/flying-cities-buckminster-fuller.htm" rel="nofollow noreferrer">https://science.howstuffworks.com/engineering/architecture/flying-cities-buckminster-fuller.htm</a></p>

CC BY-SA 4.0
2023-07-30T16:42:59.583Z
2023-07-30T16:42:59.583Z
M. A. Golding
<p>Sky Islands are a <a href="https://tvtropes.org/pmwiki/pmwiki.php/Main/WorldInTheSky" rel="nofollow noreferrer">popular sci-fi trope</a>. Think the Avatar films, the Legend of Zelda Nintendo switch games and so on.</p>
<p>Is there any configuration of exoplanets or moons that could sustain a large body of land visibly near a planet? Given some exoplanets could have the same density as styrofoam, and others are believed to be in complex gravitational systems with binary stars and other planets, moons etc. Is there any configuration that could work?</p>

CC BY-SA 4.0
2023-07-29T08:39:04.333Z
It would seem very unlikely.  I guess you don't mean "moons" because The Moon is "a large body of land visibly near" the Earth.  I guess you mean sky islands in the atmosphere, or at least within a few thousand metres of the surface, and not moving rapidly relative to the surface.  Without unobtainium, or zonai magic, that's not really possible.
James K
CC BY-SA 4.0
2023-07-29T10:03:15.480Z
It's a nice idea for science fiction, but the laws of physics apply universally & sky islands still need to obey the laws of gravity & thus would not exist.
Fred
CC BY-SA 4.0
2023-07-29T10:12:13.400Z
@JamesK: You might want to add [upsidisium](https://en.wikipedia.org/wiki/Upsidaisium) to that list. I can recall watching the Rocky and Bullwinkle [cartoon](https://www.youtube.com/watch?v=jUeTMC4QoXk) some decades ago.
Fred
CC BY-SA 4.0
2023-07-29T11:07:01.970Z
Planet made out of polystyrene, high winds, polystyrene fragments elevated as wing shapes in the airstream, something something?
tomh
CC BY-SA 4.0
2023-07-30T16:42:14.110Z
According to relativity gravity is a change in the geometry of space caused by mass. There are other theories of gravity in which gravity is a force.   And in some of those theories, it might be possible to produce negative gravity.  So possibly sky islands could be lifted up by anti gravity generators.   Otherwise floating islands would be limited to something like fuller's cloud nine concept. https://science.howstuffworks.com/engineering/architecture/flying-cities-buckminster-fuller.htm
M. A. Golding
CC BY-SA 4.0
2023-08-01T06:44:35.793Z
Of course the XKCD guy reads this and made a comic from this discussion https://xkcd.com/2809/
James K
CC BY-SA 4.0
2023-08-01T11:05:46.520Z
I mean if it's good enough for XKCD, this question deserves more upvotes!
tomh
<exoplanet>
Could sky islands exist on exoplanets or moons?
tomh
# Could sky islands exist on exoplanets or moons?

(Asked by: username_0 on 2023-07-29)

Sky Islands are a [popular sci-fi trope](https://tvtropes.org/pmwiki/pmwiki.php/Main/WorldInTheSky). Think the Avatar films, the Legend of Zelda Nintendo switch games and so on.

Is there any configuration of exoplanets or moons that could sustain a large body of land visibly near a planet? Given some exoplanets could have the same density as styrofoam, and others are believed to be in complex gravitational systems with binary stars and other planets, moons etc. Is there any configuration that could work?

**Tags:** exoplanet

> **Comments:**
> **username_1**: It would seem very unlikely.  I guess you don't mean "moons" because The Moon is "a large body of land visibly near" the Earth.  I guess you mean sky islands in the atmosphere, or at least within a few thousand metres of the surface, and not moving rapidly relative to the surface.  Without unobtainium, or zonai magic, that's not really possible.  
> **username_2**: It's a nice idea for science fiction, but the laws of physics apply universally & sky islands still need to obey the laws of gravity & thus would not exist.  
> **username_2**: @JamesK: You might want to add [upsidisium](https://en.wikipedia.org/wiki/Upsidaisium) to that list. I can recall watching the Rocky and Bullwinkle [cartoon](https://www.youtube.com/watch?v=jUeTMC4QoXk) some decades ago.  
> **username_0**: Planet made out of polystyrene, high winds, polystyrene fragments elevated as wing shapes in the airstream, something something?  
> **username_3**: According to relativity gravity is a change in the geometry of space caused by mass. There are other theories of gravity in which gravity is a force.   And in some of those theories, it might be possible to produce negative gravity.  So possibly sky islands could be lifted up by anti gravity generators.   Otherwise floating islands would be limited to something like fuller's cloud nine concept. https://science.howstuffworks.com/engineering/architecture/flying-cities-buckminster-fuller.htm  
> **username_1**: Of course the XKCD guy reads this and made a comic from this discussion https://xkcd.com/2809/  
> **username_0**: I mean if it's good enough for XKCD, this question deserves more upvotes!  

---

## 2 answers

### Answer by username_4 on 2023-08-01. Score: 3 | Accepted answer

[Earnshaw's Theorem](https://en.wikipedia.org/wiki/Earnshaw%27s_theorem) tells us that it is impossible for a stationary mass to float in a stable gravitational equilibrium, so there is no configuration of exoplanets or moons that could levitate land islands above a planet.

Levitating islands have been discussed in several Worldbuilding Stack Exchange questions:

* [Can airborne floating/flying islands be scientifically possible?](https://worldbuilding.stackexchange.com/q/33513/98864)
* [Can a planets magnetic field be strong enough to make floating continents?](https://worldbuilding.stackexchange.com/q/155959/98864)
* [Can the Meissner effect explain very large floating structures?](https://worldbuilding.stackexchange.com/q/143152/98864)

The ["official" explanation](https://james-camerons-avatar.fandom.com/wiki/Unobtanium) for the floating islands in [Avatar](https://en.wikipedia.org/wiki/Avatar_(2009_film)) is that are largely composed [unobtainium](https://en.wikipedia.org/wiki/Unobtainium#Science_fiction), a fictional room-temperature superconductor which levitates due to [flux-pinning](https://en.wikipedia.org/wiki/Flux_pinning) in Pandora's magnetic field.
This explanation is implausible but not impossible.
A [well-known video](https://www.ted.com/talks/boaz_almog_the_levitating_superconductor?language=en) reports a lift-to-weight ratio of 70,000 for a superconducting disk in a strong magnetic field gradient, so only a small fraction of unobtainium in the islands might be enough to levitate them in lesser magnetic fields. There are lots of very challenging issues about how the islands could have be initially formed with the flux pinned, and how stable the pinned flux is over geological time, but the idea is perhaps less ridiculous than I initially thought.


---

### Answer by username_3 on 2023-07-30. Score: 1

According to relativity gravity is a change in the geometry of space caused by mass. There are other theories of gravity in which gravity is a force. And in some of those theories, it might be possible to produce negative gravity. So possibly sky islands could be lifted up by anti gravity generators.

Otherwise artificial floating islands would be limited to something like fuller's cloud nine concept. <https://science.howstuffworks.com/engineering/architecture/flying-cities-buckminster-fuller.htm>


---

