I am wondering if liquid water in a ratio similar to earth's land/water ratio has anything to do with planet size. Is it possible, for instance, that a planet as big as Jupiter could have a land/water ratio similar to earth? How big/small could a planet be and still have a liguid water ocean?

Hi Al

Good Question, but I'm not certain precisely what you want to know?

Do you mean:
- ever had [and kept for millions of years] standing water, even if it was always covered with water-ice [possibly Ceres]
- ever had [and kept for millions of years] deep water with a liquid surface [e.g. probably Mars]
- has deep water with an icy surface [e.g. Europa]
- has deep water with a liquid surface [e.g. Earth]
- something else?

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These are all small 'worlds'. My thinking is that they will hold water for a short while but it will have to stay frozen or it will sublime away quickly because the size doesn't produce enough gravity to hold onto it or an atmosphere very long.

I was wondering if there was an upper limit to the size of a planet that could hold onto a liquid water ocean. I think it would not be possible for a very large planet to have a liquid water ocean. I think gravity and the heat generated by such a large body would preclude its ability to keep water in a liquid form. I am not sure why I think this. Think again about Jupiter. It's too big to have a liquid water ocean down there under the clouds, right? If it has water it is in a gas form. How big could an earth like planet be with regard to land mass/water ocean ratio? Is the size of earth part of the reason why it has and has held onto its huge oceans?

I am thinking it is not possible to ever find a Saturn/Jupiter sized or larger planet circling some sun that has an earth-like atmosphere and an earth like land/water ratio. (we couldn't live on it anyway) And I am thinking it must be the mass itself that prevents it from being anything other than a 'gas' giant. Isn't there some physics that helps understand how a planet's size determines what it can be made of?

Oh well, enough craziness from me. If I keep typing eventually the ideas behind my question may become clear even to me..., maybe.... :-)

This is an interesting question. Hopefully there's a real planetologist on the forum here [it isn't me]. I remember a Scientific American article about two years ago that talked about planet size as a function of metalicity of the proto-stellar cloud. One of the conclusions was that higher metal [later generation] stars would have heavier rocky planets. I could imagine a situation in which a rocky planet of five or ten Earth masses gets hit late in development by a body big enough for the collision to evaporate away a lot of the molecular hydrogen in the atmosphere. This might leave a more exposed core. If it were further away from the star, there may be a balance that could result in liquid oceans.

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