Creating a Planet of Sky and Clouds: Is it Possible?

[Nostredame]

Sorry if this is in the wrong part of the forum but I am a budding SciFi authro with many ideas. And I just wanted to check if one of my ideas is possible, and if not, how this effect could be best recreated.

I'm sure everyone has seen the Star Wars movies. Well if you remeber Star Wars Episode V (the second released), the characters go to a planet that is seemingly made entirely out of sky.

So my vision is a planet much like this. I envision nothing but sky and clouds, but is a planet made of sky and clouds possible? Or is it possible to have such a small core that is so dense that it produces enough gravity to maintain this atmosphere. And would it be possible to have water (in the form of clouds) on this planet?

 

[mgb_phys]

Planets made out of clouds are the most common type - gas giants Jupiter, Saturn, Uranus, Neptune make up most of the planet mass in our solar system.
These all have a rocky core due to the formation process - and an outor core of layers of liquid gas or metallic hydrogen produced by the huge pressure of all the gas on top.

You don't need a dense core to produce all the gravity - the huge mass gas will create gravity as well.
A small gas gianat isn't possible because it wouldn't have enough mass to hold onto the gas

 

[cadnr]

This is an interesting question. It's not possible to have a planet made entirely of sky because sky is is made of air (mostly gaseous nitrogen, oxygen and carbon dioxide), and so it's very light weight and wouldn't make enough gravity and would drift away into space.

If you had sufficient mass of nitrogen, oxygen and carbon dioxide to make a planet with gravity, the centre of that planet would still have to be either solid or liquid (depending on the temperature and pressure of the core), because the immense weight of gases results in them becoming compressed into liquid then solid as you go lower in altitude. The reason for this, as I'm sure you're aware, is that pressure increases with decreasing altitude.

Now, it would be very very unlikely (if not impossible) that a planet made of entirely air could ever form anyway because planets all form out of interstellar clouds which are made mostly of hydrogen. This is why the gas giants in our solar system are mostly made of hydrogen.

Hope that helps.

 

[cadnr]

To follow up on your other question, in my opinion, the most realistic way to have a "sky planet" would be to have a large terrestrial planet with a completely ocean-covered surface (like the one in attack of the clones). The atmosphere could be so thick that it's insufferably dense at sea level so the main biological activity has to occur at higher altitudes. The great density of the atmosphere at depth would also assist the buoyancy of any creatures that live in the sky (ie, making it easier to fly even if you have only small wings).