There are gas giants and there are rocky and icy planets and moons. I am curious if there could be such a beast as a planet made up entirely of liquid like water or ammonia. Think of a seemingly bottomless ocean. What would be the physics behind such a planet.
I can’t see how it could ever be possible. If a substance is liquid at surface temperatures it will have a significant vapour pressure and as a result form an atmosphere of some sort. Even a planet of pure mercury would have a thin mercury vapour atmosphere even if it never obtained any gases through bombardment of comets or radioactive decay.
There may be some odd liquids you could design that would have no appreciable vapour phase but I doubt they’d be stable under the conditions of a planetary core.
Iapetus, a moon of Saturn, appears to be composed almost entirely of water ice. Its density of 1.1 g/cc[sup]3[/sup] appears to support this analysis. If it was closer to the Sun, it could easily be liquid. So, I have no doubt tehre could be such a thing, though we currently know of none.
Wouldn’t moving it close enough to the sun to liquiefy the water result in massive evaporation and the immediate formation of a water vapour atmosphere? And of course such an atmospehre would then start getting bombarded with solar radiation and broken down into hydrogen and oxygen. Within a few thousand million years at most you’d have an appreciable water vapour and oxygen atmopshere if the planet was Earth mass.
I think you’re being too literal. Of course there’d be a significant water vapor atmosphere, but so what? Most of the mass of the planet will still be liquid.
In that case aren’t most of the ‘gas’ giants liquid planets? I was under the impression that most of their mass existed as a liquid core.
Stanley Schmidt’s novel The Web Between the Worlds features an artificial liquid satelite. The liquid content is effectivey sealed in a big plastic bag, so it stays contained and can’t evaporate or otherwise be lost.
In the ansence of gravity, things an get really big inside. It’s a huge aquarium without the usual size limits. Interesting idea.
eg “Although Jupiter may have a solid core 10-20 times as massive as Earth, some scientists think that the planet’s tremendous pressure and temperature conditions give it a liquid or slushy core at temperatures of 54,000 degrees Fahrenheit (30,000 C).”
http://stardate.org/resources/ssguide/outer_planets.html
If all we need is a planet where most of the mass exists as liquid then it seems like Jupiter may well qualify. I assumed that inkubo was asking about a planet with no atmosphere to speak of, just an infinitely deep layer of liquid material.
No argument from me.
Which brings us to the supplemtray questions:
What is the minimum mass for a body to retain water vapour at 1oC so that it can be both liquid and not gradually leak itself away into space? How about for Hg vapour? How hot would a body this massive get in the core? Would this temperature cause the planet to boil and explode, or would the pressure be enough contain the heated liquid as liquid?
Would Iapetus actually be viable if it were close enough to the sun to liquefy, or would it gradually flare away into space like a massive and extremely long-lived comet as the atmosphere gained escape velocity and got blown away by the solar winds?
Ditto Earth.
Come again? The Earth has mostly water on the surface, but most of its mass is Iron, oxygen and silicon.
Especially considering that Earth and Mercury are the densest of the planets with a specific gravity of 5.5.
A liquid planet? You would need enough gravity and surface tension to avoid the liquid from spinning off into space while rotating. Saturn is considerably less dense than water so let’s assume that this is feasible.
The next question is the core. How much pressure can a liquid hold until it soldifies? The next question is how much atmospheric pressure is needed to prevent the liquid from boiling off into space? I believe that these are both related to the planets temperature. The hotter the planet, the more pressure before the core solidifies but likewise the more atmospheric pressure needed, hence more gravity needed, hence more mass, hence more pressure on the core. Not to say that it’s impossible to have an equilibrium, but it would be really difficult and highly dependent on its orbit.
And I would bet most of that iron, oxygen, and silicon is in the mantle and outer core, which are liquid.
The mantle is not liquid.
A feature of a planet in Iain M Bank’s The Algebraist (link contains plot spoiler and nothing about the actual planet, but I felt I should link anyway :smack: )
Inceidentally, Enceladus is an ice moon losing half a ton of material a second, and this would amount to 5% of its mass over the lifetime of the solar system according to this. Presumably if it was much larger it would be able to hold on to its mass better, but I have no idea if the extra surface area would counteract this.
I suppose a sufficiently large water planet would also be able to support a thick protective ice crust to protect it while maintaining a large internal water volume.
Given that boiling point increases with pressure, I fail to see how increasing the core temperature through pressure would case a planet to boil or explode - I would have thought it more likely that currents would cause it to circulate up to cooler regions immediately, which might produce a way of keeping the the planet liquid in cold regions. However given that several of the outer planets are believed to have cores of metallic hydrogen, it might be that the water would solidify under pressure instead - clearly convection does not seem to be having much effect there.
Anyone with a degree in fluid thermodynamics in the house?
Another example from science fiction – the soviet story “Infra Draconis” describes what is essentially a water-filled moon with a rocky crust, located outside the solar system but much nearer than the stars. I don’t recall where the energy to keep this warm and liquid came from, or how it was supposed to have formed in the first place. I think the author was tryin to come up with a unique environment for life that didn’t depend on a sun. It’s in one of the two Asimov-edited volumes of Soviet Science Fiction.
Just to be clear here, there is no such mass. No matter what the parameters of your planet, it will lose atmosphere to space. The real question, is what do you need to make this take a few billion years.
I believe that I came across as too dogmatic and inflexible with my original post. I have nothing against a liquid planet having an atmosphere made up of water vapor, methane, nitrogen. Plus I’m certain it would have a core whether it was icy or rocky or a superfluid. My thoughts were that the planet was formed primarily of a liquid.
Iapetus, for imagination’s sake, replaces the moon one day because of magic or aliens or some Big Dumb Object. Other than a change in Earth’s tides and probably the convection currents within the mantle, would Iapetus turn into an oceanic moon or a slushy moon? Would Iapetus eventually disappear and become a vapor ring around the Earth eventually eroded by the sun’s emissions?
This is presupposing that Iapetus can remain in a stable orbit with Earth with little or no outside, artificial influence.