• Question: Why has so much matter accumulated on the Gas Giants - why didn't it get pulled in further towards the Sun?

    Asked by doppler to Adam, Sheila, Suzie on 24 Mar 2011 in Categories: .
    • Photo: Adam Tuff

      Adam Tuff answered on 23 Mar 2011:

      Matter is always drawn to the object that exerts the greatest gravitational pull. When the solar system formed, the planets formed seperately in what was probably an accretion disk – irregularities in the disk would have formed the planets at the time – the matter was not drawn towards the sun during formation as the protoplanets would have had a greater gravitational force on local matter. Why the outer planets are gaseous is a bit of a mystery, because we’re now starting to see gas giants very close to their parent stars.

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 24 Mar 2011:

      Near the gas giants there is a bigger gravitational pull from the planet then there is from the Sun, so just like if we went nearby in a spaceship we’d be pulled into the planet by gravity, any matter lurking nearby will do as well!

    • Photo: Sheila Kanani

      Sheila Kanani answered on 24 Mar 2011:

      It was all to do with how the solar system was formed.
      The gas giants are massive, but they are not very dense; Saturn would float in the bath if you could find a bath large enough!
      This is why they have not been pulled further towards the Sun.

Comments

  • Photo: doppler

    doppler commented on :

    Thank you! But why did so much matter in the accretion disc get so far away from the Sun anyway – or was the matter in the accretion disc formed from matter the Sun pulled towards itself, rather than coming from the Sun when it started to form? Also, why was the accretion disc in a single plane?

    • Photo: Suzie

      Suzie commented on :

      I’m not sure about the specific case of our sun, but usually planets start to form after a supernovae when the star has blown off all of its outer layers and formed a planetary nebula. It’s then surrounded by a massive cloud of dust and stuff that have blown off the star, which can then use the forces of gravity to form into planets.

    • Photo: Sheila

      Sheila commented on :

      The accreation disc was a single plane due to the gravitational pull.
      The gas was at the outer most bit of the accretion disc because it was less affected by the gravity of the forming Sun so ‘blew’ outwards and this is the gas that made the gas giants.
      They are large because they are far away from the Sun’s gravity.
      They are surrounded by moons because they are large and have their own strong gravity.

      • Photo: doppler

        doppler commented on :

        Wow, thank you! So the reason the gas planets are further from the Sun is just that the matter the terrestrial planets are made up from was heavier, so had a greater gravitational attraction pulling it towards the Sun?