Water giant?

[Daecon]

Is it possible to have a planet made out of water, like Jupiter and Saturn are made of gas?

 

I don't mean like Earth which is just covered by water, but one that is completely liquid, or a gas planet with a liquid core?

[insane_alien]

it's possible, but highly unlikely and the core would likely be solid due to the pressure, wouldn't be normal ice but one of the high pressure variants.

[DrP]

Aren't some of the gas giants moons made of ice?

[insane_alien]

you mean europa, its mostly water, the inside is kept liquid by tidal forces from jupiter, the OP was reffering to a planet the size of jupiter but made of water.

[ydoaPs]

it's possible, but highly unlikely and the core would likely be solid due to the pressure, wouldn't be normal ice but one of the high pressure variants.

 

Jupiter has a solid core?

[Klaynos]

Jupiter has a solid core?

 

Probably, quite possibly rock, and it probably has a liquid outer core... it's a difficult thing to state with much certainty though... But the pressure is so high that it's really rather likely.

[insane_alien]

i'd be very surpised if it didn't it won't be very big in relation to the rest of the planet but probably about the size of earth.

[antimatter]

Don't they all need to have slightly solid cores?

Otherwise Jupiter would be...a gas cloud instead of gas giant

[ydoaPs]

Don't they all need to have slightly solid cores?

Otherwise Jupiter would be...a gas cloud instead of gas giant

 

Why? Can you explain?

[insane_alien]

there is no requirement for a solid core, the sun does not have a solid core.

 

all that is required is that there is enough gravity present to keep the thing together. as gravitational attraction is independent of phase, this just requires you have a certain amount of stuff in roughly the same place.

[Daecon]

it's possible, but highly unlikely and the core would likely be solid due to the pressure, wouldn't be normal ice but one of the high pressure variants.

 

Would this ice have a high temperature due to the pressure?

[granpa]

water is abundant in the universe. i would assume that uranus and neptune are largely made of water. any larger than that though and it will begin to retain hydrogen and helium and become a gas giant.

[DrP]

Jupiter has a solid core?

 

The Schumacher-Levy -9 comet (if that's what it was called?) hit jupiter so hard that it made the core 'ring' apparently!

[insane_alien]

Would this ice have a high temperature due to the pressure?

 

yes, it would definitely have a high temperature from energy left over from its formation. but the extraordinarily high pressures would be sufficient to keep it solid. it would likely be a couple thousand kelvin, perhaps in the tens of thousands, depending on how old the planet is.

[Yukmay]

insane_alien said:

yes, it would definitely have a high temperature from energy left over from its formation. but the extraordinarily high pressures would be sufficient to keep it solid. it would likely be a couple thousand kelvin, perhaps in the tens of thousands, depending on how old the planet is.

 

Since we're talking about water ice here, wouldn't it be past the critical point at that temperature? In other words, no matter how much pressure is exerted on it the phase will always be a mixture of gas and liquid.

 

http://en.wikipedia.org/wiki/Image:Water_phase_diagram.svg

 

On another note, I think it's very unlikely to find a planet that is entirely water. Doesn't the current model for the accretion of the planets deal with cometary/asteroid impacts? In order to have a fully water planet with no rocky core not even a comet (dirty iceball) could have ever impacted it.

 

Yuk.

[insane_alien]

that phase diagram does not go above 10 bar(about 100m below the surface seeing as we are talking about water)

 

and the critical point deals with the liquid and gaseous phases only, above the critical point the gas phase and liquid phase have no clear transition, there is a supercritical fluid. solids phase can exist above this point but only under extremes of pressure.

[ydoaPs]

(about 100m below the surface seeing as we are talking about water)

If we're talking about Earth.

[insane_alien]

well, a local gravitational field of 10m/s^2 at T and P where density of water = 1000kg/m^2 if you want to be accurate.

[Yukmay]

insane_alien,

 

You're right. After a little more prying I was able to find an academic site with a high pressure phase diagram for water. I guess this does mean that a planet made entirely from water would have a solid core.

[Dark matter]

isn't Jupiter not entirely made out of gas, and has a central core?

[insane_alien]

it is mostly gas but some thousands of kilometers down, the hydrogen it is comprised of liquefies due to the massive pressure and eventually becomes metallic hydrogen, not to mention ices of all the other components. it is also probable that there is a mars-earth sized rocky core in the middle of it all.

 

but the large majority is gaseous.

[antimatter]

All planets have a central core...

[insane_alien]

all planets observed so far...

 

it is possible that a planet could exist as a roughly homogenous ball of gas.

 

infact, during the first generation of star formation, there would have been many not-quite stars that would be like gas giants with temperatures hot enough so they remained gaseous. sub brown dwarf but still bigger than jupiter.