Why do Gas Giants exist?



If they don’t have a solid core, where do they create their gravity to hold all the gasses into a planet shape? I’ve never understood this.

In: Physics

Gas has mass and thus generates its own gravity. Which is enough to make gas clouds collapse into spherical planets, (or stars if there is enough gas).

They still have mass (and much more of it than for example Earth).m. Mass of liquid, gas or solid is still mass and will have gravity. Gas giants are probably the first plantes to form.

They are thought to have a small solid core, just that the vast majority of the planet is gas, just like the Sun when you get that much gas into a small area/volume the gravity crushes the atoms and molecules together making the core of a gas giant denser and may even transform hydrogen from a gas to a metal. https://youtu.be/b-gCfHXNIVc

Funnily enough, we don’t actually know if gas giants have solid cores or not! However, more planet formation theories do use some sort of rocky core (protoplanet). Once that core reaches a certain mass, it starts to accrete enough gas that the gas mass helps it accrete more gas–a process called runaway accretion. This can pump up a small core from ~10 times the mass of Earth to Jupiter size or larger!

There are also theories of direct fragmentation, where gas can collapse in on itself and form a planet directly without a core required. This pathway is more akin to stellar formation and requires very massive protoplanetary disks.

Things don’t need to be “solid” in order to have mass, and mass is what generates gravity.

Further, the gas giants actually *do* have solid cores (sort of; it kind of depends on what you mean by “solid”) in that their cores are really really strange forms of hydrogen.