• Question: can you have a large planet that is not very dense so although it is large it has a low gravity?

    Asked by Arianna to Maggie, Ry, Scott on 16 Nov 2017.
    • Photo: Ry Cutter

      Ry Cutter answered on 16 Nov 2017:

      There are theories that planets like this can exist, but we haven’t seen any. It’s actually a really good idea! 😀
      .
      But, with most planet formation theories the cores get super compressed into a very heavy crystal. The core then grows proportional to the overall size of the planet, which means as the planet gets bigger it’s core grows. Density is related to volume, which means the bigger the planet gets the density grows to the power of 3 times. This meas the gravity increases faster the bigger the planet gets! This means it can be difficult to have big planets with low gravity.
      Brilliant Question!
      Ryan

    • Photo: Maggie Lieu

      Maggie Lieu answered on 16 Nov 2017:

      Yes of course, Saturn is almost the same size as Jupiter but it is half as dense and so its gravity is much less than Jupiter’s (less than half!). But a planet that is as large as Jupiter but has low gravity like Earth would be really rare because of the way planets form. The planets on the outer solar system (like Jupiter and Saturn) are so big and heavy because as they orbit the sun they have to travel a bigger distance to do 1 orbit than the closer planets like mercury and venus. This means they can gather more material and grow bigger and heavier

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