Could you create a non-gas planet the size of Jupiter or larger?
I don’t know what the theoretical upper limit is, but if you want to talk about what we know actually exists, rocky planets of up to 15 Earth masses have been found.
Spelling nitpick: The “there” you want in the title is “there” not “their.”
To answer substantively, Jupiter is not inherently different from Earth in the amount of gold, zinc, praseodymium, etc. it contains. The difference is that Jupiter is massive enough to have retained its hydrogen and helium, which are the two most abundant elements in the Cosmos. There is a point in terms of size at which a “normally formed” planet, whatever theory of planetary formation you adhere to, retains or accretes the light gases and becomes a gas giant.
That size, however, is substantially larger than Earth. I’d suspect, though I don’t have the data available to work with, that a few multiples of Earth’s mass, with equivalent increase in surface gravity, would remain a terrestrial planet.
I suspect strongly the answer is based not solely on mass but also on insolation – the amount of energy derived from the parent star – as well. Additional energy input will incrementally warm up, and thus speed up, the light-gas molecules at atmosphere top to beyond what gravity can hold them at. (See the currently-under-way “escape velocity” discussion.) Put Uranus in Venus’s orbit and let it sit for a billion years or two, and it may suffer quite a bit of ablative atmosphere loss.
Having said that much, though, let me defer to our planetary scientist members (we have one professional and several knowledgeable amateurs in the field.)
This is an interesting question, to which I don’t think we really have a good answer. I think a Jovian-size terrestrial planet is very unlikely, because such a large high element weight mass would also collect enough light gases to form a super-Jovian planet or even a brown dwarf. (We don’t actually know what is in the core of gas giants, other than that there is a substantially lower proportion of iron and other heavy metallic elements than in rocky worlds.) At some point that amount of mass would collapse and start fusing (depending on composition) or become degernerate matter; I don’t know of a well established lower bound on this.
For a long time it was assumed that gas giants only form in the outer system because the solar wind and radiative heating boil off the lighter components of atmosphere, but observations of other systems (as best we can make them) have shown gas giants in tight orbits around stars. How this happens remains to be explained. Aside from those observations, we only have the single data set from which to infer about the mechanics and probability of planet formation, and so most of what we know about planetary formation (even that of the Earth, which we can drill and test directly) is speculative.
Stranger
You’re a guest here. You’re in General Questions. I’m not sure of your meaning here, but GQ is for answering General Questions. Snarkiness belongs in the Pit.
samclem GQ moderator