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PLANETS

What’s the difference between a gas giant and an ice giant?

At their hearts, gas giant and ice giant planets are not so different. Really, a gas giant is just an ice giant with a lot more gas! The way we think that giant planets form is that an initial ball of ice and rock – a protoplanet – forms within the solar nebula, the disc of gas – mostly hydrogen and helium – and solids around a young sun. Once the protoplanet reaches about ten-times the mass of the Earth, it starts to have enough gravity to accrete solar nebula gas down on top of it. This accretion makes the protoplanet more massive, with an even better ability to grab even more gas. This gas accretion process can almost reach a runaway, with more and more gas piling on top.

The initial protoplanet is therefore the ‘seed’ for planetary formation, and that part becomes the planet’s core. Uranus