water..... or rather planet of

[eupraxia]

I know this will probably sound silly to the egg heads out there, but i watched Voyger a while ago and saw a planet intierly composed of water. Is that possible or do planet have to be composed of land and water. I know that there are planets of just land (or) rock because Mercury is one, but just water?? Does some where like Pluto which is all ice (as far as my limited knoweldge goes) Count.

Thanks for your time

[MrPahoehoe]

Well its your question, so your rules about if something counts. But a planet of pure liquid water would be extremely unlikely I would imagine. Even the sea isn't pure water after all.

You do get gas planets, e.g. Jupiter/Saturn, but unless I am mistaken they have a solid core and are made up of lots of different elements. So it seems that you could have a planet that was made up for the most part by fluids, but would likely need a solid core or something denser for the water to gravitationally accrete around.

But to have liquid water you would need to be much closer to the star and conditions are much 'rougher' around there. Most new planets of a similar distance from their star as Earth is from the sun, I believe, are subjected to intense gravitational force when the star is born which rips the remaining nebular material out of the close orbit (I think to start with these closer planets don't have atmospheres?).

To be honest, most of that is speculation, but it seems unlikely, although it would be phenomenally cool. Anyway, didn't the one on Voyager have a spacestation thingy in the centre or at least nearby maintaining it?

Thanks, that was a really great question. And it would be good to hear from anyone who isn't sort of guessing like me ;-)

[gary baldy]

I'm guessing aswell ( i saw that episode of Voyager aswell!) but our other friend is probably right about having to have a solid core. I also agree that the conditions would have to be exactly right to keep some sort of equalibrium and would have to be just the right distance from a sun etc. Saying that the earth is perfectly placed in the cosmos so there is nothing to say there is such a planet out there somewhere. I love these Cosmic type questions (even though i have no real idea what i'm talking about!)

[jake-the-peg]

Firstly you have to consider the likelyhood of water.

There is quite a bit of debate on this but the evidence is quite strong for liquid water having once existed on the surface of mars. This obviously suggests that liquid water may not be all that uncommon on planets around other stars .

As for no land masses, my geology's not the best but I would suspect that if a planet had an active core and tecktonic plate movement then you'd be almost guaranteed to get some land pushed up above a liquid surface.

But in a universe where there are as many galaxies as grains of sand on a beach and each one has a similar number of stars - it's pretty likely that somewhere there'll be a planet that at least had no land mass at some stage of it's evolution

[CT]

As a better solar system equivalent, look up Europa. The icy moon of Jupiter. It has been theorised that it may have a liquid ocean under the ice. It is tidally squeezed by Jupiter while in its orbit. This leads to heating in the core, potentially enough for a liquid ocean under the surface. The inner Galilean moon Io, is tidally stressed more (it's closer), this results in volcanic activity. So, potential for liquid water is reasonably high. IMO if you were to find a planet like this, it probably wouldn't be 100% water.