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Your question inspired me to use the Google. I’m not an expert, so I won’t offer an answer, but it was an intriguing rabbit hole!

Neptune is the smallest Jovian planet in our Solar System, and Earth is the largest rocky planet. There’s a category of exoplanets called sub-Neptunes / super-Earths that are between them in size. If one of them orbited something like Jupiter or a brown dwarf, then maybe that could happen. But it might be more of a double-planet at that point, if the larger one doesn’t quite dominate it’s orbit.

As for whether they could form like that, I’m guessing no, Jupiter had to suck in a lot of its neighborhood to get so massive, and there wouldn’t be enough left for a sub-Neptune. But perhaps it caught one when migrating out. 🤷

To piggy back on his question ive been curious about Jupiter being all gas. Doesn't it attract a lot of asteroids? And if it absorbed its neighbors it must have a rocky center right? (Obviously im missing something here just wanted to figure out what)

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Even if there's a core of silicon, carbon, nickel, and iron, it's so squished that I don't think you could call it rocks, it's some crazy form of matter that's hard for human brains to comprehend (at least my brain).

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“According to most theories, Jupiter has a dense core of heavy elements that formed during the early solar system. The solid core of ice, rock, and metal grew from a nearby collection of debris, icy material, and other small objects such as the many comets and asteroids that were zipping around four billion years ago.”

Here:

Okay, so here's some data: "A gas dwarf is a gas planet with a rocky core that has accumulated a thick envelope of hydrogen, helium, and other volatiles, having, as a result, a total radius between 1.7 and 3.9 Earth radii (1.7–3.9 R Earth); The term "super-Earth" is also used by astronomers to refer to planets bigger than Earth-like planets (from 0.8 to 1.2 Earth-radius), but smaller than mini-Neptunes (from 2 to 4 Earth-radii).

So going from this rather easily found data, I'm going out on a pretty thick limb here, but I have to say no.

Could there be a binary planetary system, which contained a mini-Neptune, and a super-earth? Probably not lol but it seems more likely than a super-earth with a mini-Neptune as a moon.

That being said, universe is so vast, and most things we've seen with JWT has made us rethink a lot of the astrophysical standard concepts.

Total copout, but maybe?

Apparently they already have found one that’s even odder, a gaseous moon orbiting a gaseous planet.

I know you said terrestrial, my sleeping medication is kicking I’m sorry, I’m signing off now! :) 🖖LLAP🖖

I heard metallic hydrogen was a possibility.

knowing the universe, i wouldn’t be suprised if there were a few gas-terrestrial binaries orbiting a barycenter dotted around our own milky way

Oh damn

Well uranus has an earth sized rocky core so an earth sized planet can handle a gasgiants gas. Venus has a decent amount of gas too while being slightly smaller. And finally the only moon in our solar system with a legit atmosphere is Titian with a methane haze orbiting Saturn. I dont think size is the defining issue but rather the conditions. Rocky planets take longer to form so it’s likely to be not enough gas by the time large rocky bodies form to start collecting gas. Its just unlikely for a planet or moon to collect a large amount of gas without collecting the most in its neighborhood without being destroyed outright, yeeted into deep space, or assimilated into whatever dominant gas giant is in the area. Id imagine the only reason our ice giants have rocky cores is because they formed further out and slower than jupiter and saturn so they had more time to collect rocky material and various ices.

It is theoretically possible for a large terrestrial planet, such as a super-Earth, to have a gas moon. In our solar system, the gas giants Jupiter and Saturn have a number of moons that are made up of gas or other lightweight materials, such as ice or rock. These moons are thought to have formed in the same way that planets do, by accreting material in the early solar system.

However, it is important to note that the conditions necessary for the formation and stability of a gas moon around a terrestrial planet would be quite different from those necessary for the formation and stability of a gas moon around a gas giant. The gravitational forces and other physical conditions present in the orbit of a terrestrial planet would be much different from those present in the orbit of a gas giant, which could affect the ability of a gas moon to form and remain stable.

Overall, it is possible for a large terrestrial planet to have a gas moon, but more research would be needed to determine the specific conditions under which this might occur and how such a moon would behave.

TOI-849b is a rocky planet 40 earth masses in size (https://www.nationalgeographic.com/science/article/bizarre-planet-largest-known-rocky-world-40-times-as-massive-as-earth)

Kepler 138d is a mini Neptune gas giant 2.1 times heavier than the earth meaning TOI-849b is 19 times larger than it.

Charon and Pluto have a 2:1 mass ratio meaning a 19:1 ratio can definitely be stable and is not really a double planet system.

Also how this can be formed TOI-849b is believed to be the core of a massive gas giant which somehow lost its gaseous layers (there are inconclusive theries on how), so maybe it could have had the moon from when it was larger or maybe the moon was a Rogue planet that was captured in orbit.

The likelihood of this configuration is very low but I would say it is possible and the universe is huge so maybe it could happen somewhere.

The core of Jupiter is likely rocky. I’ve seen out there claims it could be a giant diamond, but that’s unlikely.

The inner core of Jupiter is likely rock around the diameter of Earth. The outer core is liquid metallic hydrogen: not quite dense enough to be a complete plasma (electrons stripped from the atoms), but dense enough to act as a metal in the chemistry sense of the word (electrons can flow freely). This is why Jupiter has such a strong magnetic field, as magnetic fields require liquid metal that moves (Jupiter rotates in around 10 hours).

In fact, if you use an old TV with bunny ears to pick up the broadcasts, and you tune it to a station without anything so you see the snow, that snow is composed of / caused by three things: the Sun’s magnetic field, Jupiter’s magnetic field, and the Cosmic Microwave Background (CMB).

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As is mine. Hurray for Lunesta

KSP 2 devs looking for ideas for some new content.

They might throw a binary gas-terrestrial system somewhere in the outer edges of the kerbal galaxy

That inner core would be liquid rock, no? Must be insanely hot in there.

I mean, the Earth’s inner core is solid due to the high pressure. My understanding is that gas giants’ cores are also solid due to the even higher pressure.

Hello u/The-Sturmtiger-Boi, your submission "Is it possible for a large terrestrial planet, like a super earth, to have a gas moon?" has been removed from r/space because:

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