Astronomy Blog

Planet definition outcome

The IAU have live streaming from the General Assembly about the last draft resolution for the definition of planets. Jocelyn Bell Burnell was chairing the debate (which she does well). It has now finished and the results are finally in although there were votes on having revotes and I think everyone was getting a bit tired. Here are the basic results.

• Pluto is now a dwarf planet and the traditional eight are just plain planets (the term "classical" was voted down).



• Ceres is a dwarf planet.



• 2003 UB313 is probably a dwarf planet.



• A new class of objects has been created of which the first example is Pluto. These objects lay beyond the orbit of Neptune but are dwarf planets. Presumably this includes 2003 UB313.



• Charon is just a moon because it is not the "dominant" body in its neighbourhood.
  

However, Resolution 6b was voted against (as was a recount) so the classification for the objects of which Pluto is the first example has no name. The results is that a committee must now be set up to give it a name.

So we have 8 planets. We have several dwarf planets (Pluto, Ceres, 2003 UB313 and perhaps also 2005 FY9 and 2003 EL61). There is a new class of objects - as yet un-named - which include all the dwarf planets that are beyond Neptune ie. all but Ceres. Is that clear now?