I was watching a Star Trek: Voyager episode called thirty days, which features a great spherical ocean in space, and it got me thinking.
We have gas planets which are nearly entirely gas (I’m sure there is some solid near the centre - either from comets or from compression), and planets that are made of rock.
Are there any liquid planets?
I know that water is very scarce, but could there be a water planet out there somewhere in the Galaxy? Or is there some reason why this could never happen?
If Jupiter had wandered closer to the sun, Europa would be a water world.
Water is not uniformly distributed throughout the galaxy, so planets forming in water rich regions, such as the Orion nebula may accrete more water than the earth did.
Actually water is composed of the two most common chemically reactive elements in the universe. The outer planets in our solar system probably contain more water than the solid mass of all the inner planets. The trick would be to contrive a situation where water, but not large amounts of free hydrogen and helium, could condense. Another consideration is that ultraviolet radiation from the sun tends to break down chemical compounds at the top of an atmosphere, letting the lighter hydrogen escape into space.
Just having the planet form close enough to the star, but not too close - like Earth, and having it roughly Earth mass will do that, I’d think. And having oxygen producing life evolve ( for an ozone layer ). After all, we have Earth as proof that such conditions allow liquid water without a thick blanket of hydrogen and helium.
I don’t know enough about water to explore the question fully, but I wonder whether even water, notoriously incompressible as it is, could withstand the pressure of thousands of miles of water above it and stay in a liquid form.
At a high enough pressure, water becomes one of four solid forms; a water planet the size and internal temperature of the Earth would certainly have a core of ice X.
IANA physicist, but ISTM that ya gotta have a dense core for anything big enough to call a “planet” - or even a “plutoid” - iron, or at least rock, to form in the gravitational field of a mass that will become a star. Yeah, yeah, suns are - for all practical purposes - at least 99% hydrogen, and in the early universe there wasn’t anything else, but …
No human has ever observed the process of star formation. And we do know that some relatively young stars have anomalously high levels of other elements in them (which makes them look different and behave strangely). Wanna bet that at least some of them didn’t coalesce around a core of denser elements? Or maybe they had some planets that got too close to Papa and fell in. I dunno, but it’s an interesting thing to speculate about.
Huh? At the moment atoms coalesced from the fiery maelstrom of the big bang, the universe was 75% hydrogen and 25% helium and almost nothing else. It still is, although trace amounts of heavy elements have formed in supernovas since then. Nevertheless, stars and then galaxies were able to form. Hydrogen, light as it is, has mass. Put a big cloud of it in space with no other objects around and eventually, areas of slightly higher density will from and begin to pull in more gas from the force of gravity alone. You don’t need a solid anything to get this process going; only mass–any mass. First generation stars were ALL hydrogen and helium; only later generation stars like our own Sun contain any heavy elements.
And I’m not sure what you mean by humans never observing the process of star formation. True, we don’t live nearly long enough to observe the process from start to finish of any given star, but we can look around the observable universe and see the process occurring at every stage of the process. Not only that, but we’ve seen it for nearly the entire range of stellar masses.
Although controversial, the “Snowball Earth” hypothesis posits the Earth itself completely covered by ice. The continents weren’t submerged, but covered by glaciers. Still, it’s a water surface (albeit frozen) from pole to pole.
Jupiter is made of liquid. ‘Gas giant’ is a misnomer. There’s an atmosphere, but the hydrogen forms a sea. Deeper down it becomes “metallic” liquid hydrogen and eventually in the center it’s just solid. Mostly it’s liquid however.
Come to think of it the Earth is liquid too.
Covered in water, yes, but not made of water. It’s a big hunk of rock with a thin covering of (probably) liquid water and a light crunchy topping of ice.
Mmm, just like momma used to make.
I certainly don’t dispute your statement about the still minuscule quantities - by comparison with the whole - of heavier elements to the total matter content of the universe (as opposed to its entire content, of which all matter seems to be an unimpressively small percentage). All this despite 13+ billion years of supernovas and novas spewing out significant percentages of their lifetime heavier element production in their death throes.
I was under the distinct impression, gained mostly from articles read - quite avidly; I’ve been a SF reader for >50 years now - in SciAm (and some in Analog, to be sure) that in the initial makeup of the universe following the Big Bang, both the quantity and the percentage of helium was “trivial”. Now, (alas, 'tis true) I am getting to be an old lady, and perhaps I am remembering wrong. However, if this is so, I’d appreciate references, links, or whatever to support the percentages you give.
As for observing star formation at every point (in the snippage, which I won’t bother to paste back), I question this. It may be that the new space observatories which will monitor different radiation frequencies than those already in service, and due to come on line in the next decade or so (if all goes well), will give is a more complete picture of the processes. However, all I’ve seen seems to indicate that it’s still quite sketchy. Of course the investigators consider their data as a whole, and interpolate along the curve they perceive, but that’s not a complete - nor necessarily a correct - view. APoD is set as my browser home page; I love looking at images of the heavens - especially of galaxies, gas clouds and planetary nebulae. I read what they have to say, too, and often follow their links.
I most humbly suggest that cosmologists and astronomers have an even less complete view of the process of star formation than physical anthropologists have of human evolution. This may - hopefully will - become much more complete as data from a broader range of radiation frequencies being monitored by telescopes, especially from ones in space, where the atmosphere and other impediments reduce the amount of available data, increase. But I truly don’t see how it is possible to form more than theoretical view of anything for which accurate and complete observational data - start to finish - of a process (any given process) are obtained.
There are two processes that take millions to billions of years to complete. One is the formation of a new solar system - which may happen in a few million years (but I am not persuaded it happens that quickly). The other is the evolution of life, from the first simple prokaryotes to large organisms with complex brains (whether or not sapient, or even merely sentient [i.e., capable of feeling and emotion, as many complex animals are]). On Earth, the evidence suggests that took at least a billion years, even though it sppears to have begun when the planet was barely cooled from its initial coalescence - and that’s assuming that some dinosaurs and early mammals were sentient (which is likely not the case).
Assuming the human race lasts so long, our extremely distant descendants may have the data. We never shall.
Thanks, but that site didn’t really explain it well enough for me to be satisfied. However, the Wikipedia article Big Bang nucleosynthesis did it in a way that removed all doubts. It even brought in the ratio of protons to neutrons to explain just why helium is so abundant.* Fairly obviously, it was written by someone who understands the subject, and can write decently (not always the case, whether the writers are scientists, science writers, or (for that matter) English comp majors - and definitely of Wiki contributors).
<rant>Of course, writing is a skill which requires both talent and training - and too few people, even among the educated, have teachers who are sufficiently skilled themselves, and also dedicated, teaching students who are willing to apply themselves to the difficult task of learning</rant>
*Pity the helium supply on Earth is so limited - and that so much of it is dedicated to the frivolous business of supplying those idiot balloons they sell for kids, celebrations, get well, etc. Not to mention what the metalicized plastic of the balloons is doing to critters who eat them, after the balloons escape or are tossed.
Exactly. I want to know if somewhere out there is a swirling mass of water (with a solid core of compressed water)
Au contraire
I think it’s very possible. You don’t need to go to Orion’s nebula to see water worlds. Just go past Neptune. It’s all ice there. Water’s in fact the second most abundant molecule in the universe, after dihydrogen.
The only trick would be getting all that water into the temperate zone. This is the tough part, since the reason the rocky planets are rocky is that all the non-rock’s boiled off (think a comet’s tail). But if a large object like Eris or an even bigger trans-Neptunian found itself repositioned in an Earth-like orbit around its star, it would turn into one giant ocean. Interestingly, though, that water may be sullied by floating crude oil and plastic.
Bolding mine. You’d be surprised:
So you’re saying that the magazine article I saw deprecating that use was exaggerating? 
They did talk about the important uses of it for science, and complained of wasting it on balloons. Of course, they were even more scathing about the role the lost and deflated metallicized plastic balloons play in the deaths of birds and animals.