Why the Word 'Planet' Will Never Be Defined

eldavojohn writes "What makes a planet a planet? Slashdot covered the great debate about whether or not Pluto qualified and Space.com now has up an article explaining why we'll never have the term 'planet' defined to a point that everyone can agree on. Divisions in the scientific community currently stand over whether or not it has to be in orbit around a star, the dynamics of the body in question and apparently the country you come from plays a part in it too. Some feel the United States is the dominant deciding factor on the definition but the IAU has not turned to democratizing the definition yet." From the article: "In the broadest terms, a planet could be thought of as anything from an 800-kilometer-wide (500-mile-wide) round rock orbiting a dead star to a colossal gas ball floating alone in space."

Background info

[Anonymous Coward]

This [wikipedia.org] article has some good background info. Also see the article on the redefinition [wikipedia.org].

Re:VERY IMPORTANT

[SQLGuru]

The parent post is spam. Please do not click it. It redirects to http://31337.pl/ [31337.pl]

Layne

The real problem

[edwardpickman]

There can't be one definition because there are three classes of planets. Gas giants, rocky planets and icy planets. The big argument is whether to include icy planets but icy planets are closer to earth than gas giants so how do you include one but not the other? The sensible definition to come up with three classes and require them to orbit the sun to exclude moons and to have sufficent gravity for a roughly round shape, the Earth isn't perfectly round. What it would leave us with is four rocky planets, four gas giants and a similar number of icy planets. The Oort cloud gets tougher. Since they still orbit the sun it might be wise to come up with a fourth definition of outer planets for any Oort Cloud objects. One excuse for eliminating Pluto was it's eliptical orbit but most planets have eliptical orbits so that factor gets arbitary. Splitting the definition avoids demoting any planets and allows for new objects including some that may not fit well with the current definition.

Planet Classes

[bill_mcgonigle]

A better way to do it would be to set a minimum atmosphere, size, density for Planet/Dwarf Planet/Asteroid/Gas Giant classification...A nomenclature similar to Chemistry is needed.

Quite right. They're all planets but of different classes. We could list up all the types of planets we know about and assign alphabetic class numbers to them. An Earth-type planet could be, "Class M [wikipedia.org]". I know, wild, original idea...