A Case of the Plutoids

Do you remember the momentous events of summer 2006? You mean you've forgotten already? It was at the International Astronomical Union's General Assembly in Prague. How could you have forgotten that? Despite all the hugely interesting astronomy and astrophysics that was being presented at the General Assembly, the main topic of interest for some surrounded the definition of the term 'planet'. This was discussed at great length on my blog at the time and I'm now totally apathetic.

One outstanding matter from that General Assembly was the need for a decision on the name for the class of dwarf planets beyond the orbit of Neptune. The term Pluton was initially suggested but rejected once the geologists pointed out that the term was already used for a type of rock. The wording of the final resolution had settled on "plutonian object" but that was also rejected in the final vote and the IAU told to go off and think of a better name. Now, two years later, they have settled on Plutoids. Don't panic, I'm sure there will be a cream for it.

A plutoid is an object orbiting the Sun at a distance (semi-major axis) greater than that of Neptune, whose self-gravity is strong enough for it to be in hydrostatic equilibrium, and has cleared the neighbourhood around it's orbit. For practical purposes, an object's absolute magnitude will be used to work out if it is to be classed as a plutoid. I worry that that will cause problems for the future.

If you are the type of person who really likes to have well defined boxes for your solar system objects, you may like to know that the two currently known plutoids are Pluto and Eris.

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Posted in astro blog by Stuart on Wednesday 11th Jun 2008 (16:56 BST) | Permalink
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