• Question: how come there are dwarf planets?

    Asked by to Joe, Juan, Kate, Rory, Rosie on 20 Mar 2014. This question was also asked by .
    • Photo: Rosie Coates

      Rosie Coates answered on 20 Mar 2014:


      well @jimbobs, I guess the short answer to that question is that they’re just not big enough to be planets…

      For the longer explanation of why there are dwarf planets we first have to think about how planets are formed.

      Way back when our galaxy was formed about 13 billion years ago from a big cloud of swirling dust this dust started collecting in smaller swirling clouds. Asteroids in these swirling clouds started crashing into each other to make bigger asteroids and eventually some of these became big enough to be called planets. Now the definition of a planet is something that orbits a star, has enough gravity to pull itself into a spherical shape and has cleared the neighborhood of its orbit.

      Poor old Pluto is possibly the most notorious example of a dwarf planet. Pluto had the status of planet for all of 76 years before the Kuiper belt was discovered. The Kuiper belt is a an area of our galaxy, on the same orbit around the sun as Pluto, that contains spherical bodies of masses the same and even larger than Pluto.

      After the discovery of the Kuiper belt scientists unfortunately had to demote poor old Pluto as it just wasn’t big enough to clear its neighborhood. What do I mean by “clear its neighborhood”? Well basically I mean that it just didn’t have enough gravity to either sling the other bodies, or dwarf planets of the Kuiper belt, out of its orbit or absorb them (read some more about this here: /caesiumm14-zone/2014/03/17/is-it-true-that-jupiter-is-protecting-us-from-asteroids-as-it-is-a-lot-bigger-than-earth/)

      So to sum up there are dwarf planets because when the galaxy formed the dwarf planets just didn’t experience enough collisions to give them enough mass to dominate their orbits.

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