Planet debate gets greater

[n2doc]

Posted: Friday, September 19, 2008 7:12 PM by Alan Boyle

A. Feild / STScI / NASA / ESA
An artist's conception shows the dwarf planet Haumea
and its two moons, Hi'iaka and Namaka.
So just how many planets are there in our solar system anyway? Eight? Nine? Thirteen? Or thousands? Far from settling the question, the "Great Planet Debate" has revealed just how complex and interesting the question is.

The planethood question got more interesting this week with the naming of yet another dwarf planet, Haumea. It's traditional to name planets after mythological deities - and Haumea, the Hawaiian goddess of childbirth and fertility, follows that formula.

The football-shaped world was found by Caltech astronomer Michael Brown just after Christmas 2004 (which prompted its initial, unofficial nickname: "Santa"). Haumea's discovery was shrouded in a scientific controversy that Brown recaps in his Weblog. At the time, controversy surrounded its planetary status as well, because it added to a growing class of objects in the same general class as Pluto. Astronomers surmised that hundreds of Pluto-scale objects may lurk on the icy rim of the solar system's disk, known as the Kuiper Belt.

The controversy came to a head in 2005 when Brown's team found the object now known as Eris - a world like Pluto, only bigger and farther out. All this led the International Astronomical Union to agonize over where to draw the line on planethood. In 2006, the IAU came up with a definition aimed at putting the solar system's eight biggest planets in one class, and Pluto in a different class with Eris and other dwarf planets or "plutoids."

more:
http://cosmiclog.msnbc.msn.com/archive/2008/09/19/1426108.aspx