<p>Buoyancy, following <a href="https://en.wikipedia.org/wiki/Buoyancy#Archimedes&#39;_principle" rel="nofollow noreferrer">Archimedes' law</a>, depends on the volume the body and the density of displaced material. The force is 
$$ F_{buoy} = \rho_{gas} \cdot V_{body}\cdot g$$
which has to act against the bodies' own weight $F_{weight} = -m_{body} \cdot g$.<br>
Here $\rho$ is density, $V$ is Volume, $g$ the local gravity.</p>

<p>If you're referring to <a href="https://www.youtube.com/watch?v=HoCAxS4vqwQ" rel="nofollow noreferrer">this</a> video, then the aerogel that was created in the 1980's is essentially a high-tech balloon.</p>

<p>There are a few points that need discussion here.</p>

<p><strong>1. Balloons the size of continents don't occur naturally anywhere.</strong><br>
I think we can take this as given.</p>

<p><strong>2. The filling gas</strong><br>
acts to decrease $F_{weight}$ and its pressure must be enough to hold up the body volume. Else the body will collapse and the buoyancy decreases to zero.  </p>

<p>A floating continent would need some appropriate filling gas in large quantities, that has lower density than the gas giant atmosphere.<br>
Impossible is a strong word, but this seems very impossible to me. Also for the continent then be able to uphold its structure under its own weight would be very difficult.</p>

<p><strong>3. Particles either float or experience drag.</strong><br>
If they float, they're coupled to the gas flows. Once they would grow larger, they start experiencing gas drag. When this happens, they loose their momentum and are dragged down into the depths of the planet.<br>
They then will contribute to the structure of the deep planet, but are lost to any continent-building process.</p>

<p>So even if your floating continents seem impossible, I think is not a stupid question at all. I might just throw this on our students and test their understanding of buoyancy!</p>

CC BY-SA 3.0
2018-04-14T17:04:43.107Z
2018-04-14T17:04:43.107Z
AtmosphericPrisonEscape
<p>This may be a very stupid question, as I know little about astrophysics, but if solids like Aerogel can float in gasses like sodium hexafluoride, could there be pressures high enough on gas giants to compress a gas to the point where solid particles such as dust collide and create floating landmasses?</p>

CC BY-SA 3.0
2018-04-14T15:19:27.203Z
Air balloons... you don't need very dense gas for that, it is possible even in air.
peterh
CC BY-SA 3.0
2018-04-14T15:21:09.237Z
I mean natural formations.
William Grannis
CC BY-SA 3.0
2018-04-14T15:27:06.840Z
Could you add a source/link to the floating aerogel? There's a misconception here, but I can't resolve it, until I don't know why this one floats.
AtmosphericPrisonEscape
CC BY-SA 3.0
2018-04-14T15:36:19.983Z
The link to the video doesn't seem to work.  Google floating aerogel.  It should be the first video.
William Grannis
CC BY-SA 3.0
2018-04-15T19:22:54.963Z
Uhm, okay! Aerogels are very sophisticated materials, their creation by natural processes is very unlikely. Furthermore, dense gases are also very rare things in a Universe from 99% H and He.
peterh
CC BY-SA 3.0
2018-04-16T15:39:54.230Z
Lots of solids float in $NaF_6$ .  It's used for "showoff" videos with, e.g., little toys floating in apparently empty fishtanks.
Carl Witthoft
<gas-giants>
Floating Masses in Gas Giants
William Grannis
# Floating Masses in Gas Giants

(Asked by: username_0 on 2018-04-14)

This may be a very stupid question, as I know little about astrophysics, but if solids like Aerogel can float in gasses like sodium hexafluoride, could there be pressures high enough on gas giants to compress a gas to the point where solid particles such as dust collide and create floating landmasses?

**Tags:** gas-giants

> **Comments:**
> **username_1**: Air balloons... you don't need very dense gas for that, it is possible even in air.  
> **username_0**: I mean natural formations.  
> **username_2**: Could you add a source/link to the floating aerogel? There's a misconception here, but I can't resolve it, until I don't know why this one floats.  
> **username_0**: The link to the video doesn't seem to work.  Google floating aerogel.  It should be the first video.  
> **username_1**: Uhm, okay! Aerogels are very sophisticated materials, their creation by natural processes is very unlikely. Furthermore, dense gases are also very rare things in a Universe from 99% H and He.  
> **username_3**: Lots of solids float in $NaF_6$ .  It's used for "showoff" videos with, e.g., little toys floating in apparently empty fishtanks.  

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## 1 answers

### Answer by username_2 on 2018-04-14. Score: 3 | Accepted answer

Buoyancy, following [Archimedes' law](https://en.wikipedia.org/wiki/Buoyancy#Archimedes'_principle), depends on the volume the body and the density of displaced material. The force is
$$ F\_{buoy} = \rho\_{gas} \cdot V\_{body}\cdot g$$
which has to act against the bodies' own weight $F\_{weight} = -m\_{body} \cdot g$.  
Here $\rho$ is density, $V$ is Volume, $g$ the local gravity.

If you're referring to [this](https://www.youtube.com/watch?v=HoCAxS4vqwQ) video, then the aerogel that was created in the 1980's is essentially a high-tech balloon.

There are a few points that need discussion here.

**1. Balloons the size of continents don't occur naturally anywhere.**  
I think we can take this as given.

**2. The filling gas**  
acts to decrease $F\_{weight}$ and its pressure must be enough to hold up the body volume. Else the body will collapse and the buoyancy decreases to zero.

A floating continent would need some appropriate filling gas in large quantities, that has lower density than the gas giant atmosphere.  
Impossible is a strong word, but this seems very impossible to me. Also for the continent then be able to uphold its structure under its own weight would be very difficult.

**3. Particles either float or experience drag.**  
If they float, they're coupled to the gas flows. Once they would grow larger, they start experiencing gas drag. When this happens, they loose their momentum and are dragged down into the depths of the planet.  
They then will contribute to the structure of the deep planet, but are lost to any continent-building process.

So even if your floating continents seem impossible, I think is not a stupid question at all. I might just throw this on our students and test their understanding of buoyancy!


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