I Does gravity compress matter in planets?

[Dreksler]

TL;DR Summary

If for example a planet is fully made out of water ice and is 1,000 km in diameter its density will be 1 g/cm3 (I assume), does that mean that a planet fully made out of water ice at 10,000 km in diameter will also have a density of 1 g/cm3 or will it be greater due to (possible) compression because of greater gravity?

Will there be a compression of matter that the planet is made out of due to gravity when we are talking about planets? If so I would like to know what the effect would be in the example given in the summary.

 

[fresh_42]

What have you read about Jupiter?

 

[Dreksler]

What have you read about Jupiter?

Didn't read much about Jupiter recently. The interest in the question started while I was reading up on Super Earths and their composition.

 

[fresh_42]

Jupiter is an example where such a compression takes place. For any other planet, you need to provide far more data.

 

[Dreksler]

Jupiter is an example where such a compression takes place. For any other planet, you need to provide far more data.

I recall something regarding that, possibly that in the back of my mind made me ask the question in the first place. I don't know exactly what more data is relevant to the question. Let's say a fully solid with no gasses planet that is entirely made out of water ice with a diameter of 1,000 km compared to a fully solid water ice planet with no gasses at 20,000km, both will have a density of about 1 g/cm3?

 

[fresh_42]

https://en.wikipedia.org/wiki/Pressure_melting_point

 

[Ibix]

I would imagine the latter would be more dense, but it would depend on how recently it formed (gravitational collapse would cause significant heating). The details would be theoretically calculable by looking at a phase diagram of water and specifying a temperature, but I've no idea if we have reliable information about the physical properties of water under that kind of pressure.

In short, I don't think it's as simple as specifying a radius. At the least you need to do a back of the envelope calculation of the pressure at the center then find a phase diagram valid to that kind of pressure. The former's fairly easy, but the latter may or may not exist.

 

[fresh_42]

The former's fairly easy, but the latter may or may not exist.

See my Wikipedia link in post #6.

 

[russ_watters]

Summary:: If for example a planet is fully made out of water ice and is 1,000 km in diameter its density will be 1 g/cm3 (I assume), does that mean that a planet fully made out of water ice at 10,000 km in diameter will also have a density of 1 g/cm3 or will it be greater due to (possible) compression because of greater gravity?

Look into the density at the bottom of the ocean for a light version of this.

 

[JLowe]

There's also temperature and salinity to consider with the ocean water.