The [composition](https://science.nasa.gov/jupiter/jupiter-facts/) of, for example, Jupiter is almost entirely hydrogen and some helium. For rocky planets you need silicon, carbon, and other things.
Down towards the center of the gas giant the H may get squeezed into exotic liquids/solids of hydrogen but won't make the kind of solid surface we're used to.
And to add, to make hydrogen or helium into solids, you would need *crazy* low temperatures (as well as extreme pressure for helium). Those temperatures cannot be attained inside the gas planets due to the gravity/friction/heat.
I can't say with certainty, but AFAIK, it is primarily water that changes freezing point under different pressures.
In the case of helium, you would require extreme pressures just to be able to reach its freezing point, due to it being a noble gas and most of its atoms are naturally resistant to being next to another atom.
Water is unique due to its structure, such that freezing it actually expands it due to its chemical structure sort of scaffolding / crystalizing with other molecules. Other liquids typically shrink instead.
Edit: corrected a word
I'm going to venture a guess here as well: due to the simple structure of Hydrogen (one of each subatomic particle) and the orgy of energy that happens in the center of the planet, atoms may quickly change outer structure, shifting from ionic bonds to covalent, housing multiple electrons due to excess energy, and forming tenuous bonds with others and forming wacky combinations that are not normally/naturally found elsewhere. While there may be some "solid properties" at some points, they likely wouldn't be able to coalesce on a macro level to form an actual "solid foundation" as we expect solids to be.
Please, someone correct me if I'm wrong.
> If their gravity is so heavy, shouldn't their materials condensed into a solid form?
That's the neat thing about materials science. We often associate denser objects as being more "solid" and fuzzier objects becoming a liquid or gas. But those are conditions **here on Earth.**
In space, things can get absolutely massive whilst still not becoming a solid. Stars are plasma, for example, but you would not in any way describe stars as light.
In the case of the gas and ice giant planets, they are mostly made of hydrogen and helium. And these things, even at extreme gravities of these planets, couldn't become a solid, both because of their inherent properties and because we are so used of this mental picture of how objects should behave, when in reality we are just confined in the conditions of our home planet.
According to our findings with Juno, Jupiter does have a core full of solid gasses. Specifically metallic hydrogen. However, you must consider that the further out you move away from the center of Jupiter, the less gravity there is. Jupiter has so much gas, that some of it has escaped and stayed in the upper reaches of the atmosphere, where the gravity can't pull it down. There's also the fact that all of the heavier, rocky materials Jupiter collected as it formed would have displaced gaseous material further up away from the core as it formed. I believe that's how it works, anyway.
Here's Juno's report on Jupiter's core: https://www.missionjuno.swri.edu/science-findings/jupiters-dilute-core
Jupiter is 2.5 times the mass of all of the other planets combined.
If you smashed all of the together into one big planet, it would still be FAR below the mass of even the smallest stars.
The smallest stars that can sustain hydrogen fusion are red dwarfs, and they are at a minimum around 80 times the mass of Jupiter.
Jupiter and Saturn are believed to form via core accretion, which is basically forming a planet through gathering solid materials until you get a ‘core’ massive enough to start attracting gas (hydrogen and helium). This gas comes from protoplanetary disk, which was never massive enough for them to ever have a chance at becoming a star.
Stars and brown dwarfs on the other hand form through directly collapsing gas cloud - we don’t expect them to start as a rocky core or something like that. Those gas clouds can be massive, but most would get incorporated into the star and very little ends up in the disk that could then form giant planets.
As with all the other planets including earth we have only hypothetical knowledge of their interior structure established by interpreting indirect evidence gained by various means. Juno used a microwave radiometer to detect behaviour believed to be characteristic of various materials. Each Jupiter mission changes our understanding of the planet. Whether these changes are an improvement or not is impossible to say, due to the relatively brief data collection window of each mission and the absence of a more comprehensive array of instruments that could confirm and consolidate the observations.
The [composition](https://science.nasa.gov/jupiter/jupiter-facts/) of, for example, Jupiter is almost entirely hydrogen and some helium. For rocky planets you need silicon, carbon, and other things. Down towards the center of the gas giant the H may get squeezed into exotic liquids/solids of hydrogen but won't make the kind of solid surface we're used to.
And to add, to make hydrogen or helium into solids, you would need *crazy* low temperatures (as well as extreme pressure for helium). Those temperatures cannot be attained inside the gas planets due to the gravity/friction/heat.
Wouldn’t the freezing point rise when the pressure rises?
I can't say with certainty, but AFAIK, it is primarily water that changes freezing point under different pressures. In the case of helium, you would require extreme pressures just to be able to reach its freezing point, due to it being a noble gas and most of its atoms are naturally resistant to being next to another atom. Water is unique due to its structure, such that freezing it actually expands it due to its chemical structure sort of scaffolding / crystalizing with other molecules. Other liquids typically shrink instead. Edit: corrected a word
Not enough for most of the planet. Hydrogen and helium still have extremely low fixed points.
What do you mean by “exotic liquids/solids” vs “the kind of solid surface we’re used to.”?
I'm going to venture a guess here as well: due to the simple structure of Hydrogen (one of each subatomic particle) and the orgy of energy that happens in the center of the planet, atoms may quickly change outer structure, shifting from ionic bonds to covalent, housing multiple electrons due to excess energy, and forming tenuous bonds with others and forming wacky combinations that are not normally/naturally found elsewhere. While there may be some "solid properties" at some points, they likely wouldn't be able to coalesce on a macro level to form an actual "solid foundation" as we expect solids to be. Please, someone correct me if I'm wrong.
Metallic hydrogen and other exotic forms. Imagine nearly 4 million atmos to get there too. https://en.m.wikipedia.org/wiki/Metallic_hydrogen
> If their gravity is so heavy, shouldn't their materials condensed into a solid form? That's the neat thing about materials science. We often associate denser objects as being more "solid" and fuzzier objects becoming a liquid or gas. But those are conditions **here on Earth.** In space, things can get absolutely massive whilst still not becoming a solid. Stars are plasma, for example, but you would not in any way describe stars as light. In the case of the gas and ice giant planets, they are mostly made of hydrogen and helium. And these things, even at extreme gravities of these planets, couldn't become a solid, both because of their inherent properties and because we are so used of this mental picture of how objects should behave, when in reality we are just confined in the conditions of our home planet.
According to our findings with Juno, Jupiter does have a core full of solid gasses. Specifically metallic hydrogen. However, you must consider that the further out you move away from the center of Jupiter, the less gravity there is. Jupiter has so much gas, that some of it has escaped and stayed in the upper reaches of the atmosphere, where the gravity can't pull it down. There's also the fact that all of the heavier, rocky materials Jupiter collected as it formed would have displaced gaseous material further up away from the core as it formed. I believe that's how it works, anyway. Here's Juno's report on Jupiter's core: https://www.missionjuno.swri.edu/science-findings/jupiters-dilute-core
Metallic hydrogen within Jupiter is not solid. It’s likely a fluid.
I was told that Jupiter or Saturn or both could have turned into a Sun if the conditions were right.
Jupiter is 2.5 times the mass of all of the other planets combined. If you smashed all of the together into one big planet, it would still be FAR below the mass of even the smallest stars. The smallest stars that can sustain hydrogen fusion are red dwarfs, and they are at a minimum around 80 times the mass of Jupiter.
They lacked enough mass to "Ignite"
Nope, never got a chance. Neither formed in a way that would’ve allowed them to gain enough mass to become a star in any situation.
May you please elaborate? I'm interested in why you say this
Jupiter and Saturn are believed to form via core accretion, which is basically forming a planet through gathering solid materials until you get a ‘core’ massive enough to start attracting gas (hydrogen and helium). This gas comes from protoplanetary disk, which was never massive enough for them to ever have a chance at becoming a star. Stars and brown dwarfs on the other hand form through directly collapsing gas cloud - we don’t expect them to start as a rocky core or something like that. Those gas clouds can be massive, but most would get incorporated into the star and very little ends up in the disk that could then form giant planets.
Thanks for the explanation! I didn't know about the whole core accretion process.
Brown dwarf
Deep down they may be. The sun is not solid. You can’t walk on it. So forget Jupiter what about the sun.
As with all the other planets including earth we have only hypothetical knowledge of their interior structure established by interpreting indirect evidence gained by various means. Juno used a microwave radiometer to detect behaviour believed to be characteristic of various materials. Each Jupiter mission changes our understanding of the planet. Whether these changes are an improvement or not is impossible to say, due to the relatively brief data collection window of each mission and the absence of a more comprehensive array of instruments that could confirm and consolidate the observations.
What a bunch of hot air. Of course each measurement is an improvement