[meteorite-list] 'Plutons' Push Planet Total Up To 12

[Ron Baalke]

http://news.scotsman.com/scitech.cfm?id=1194292006

'Plutons' push planet total up to 12
JOHN VON RADOWITZ
The Scotsman
August 15, 2006

A NEW kind of planet, the "pluton", could soon be taking its place in the 
Solar System. 

Astronomers have agreed on a draft proposal for redefining what 
constitutes a planet. 

If approved at a meeting underway in the Czech capital, Prague, school 
science text books will have to be re-written. 

The new definition would mean there are 12, not nine planets, and more 
could be added to the list in the future. 

They include eight "classic" planets - Mercury, Venus, Earth, Mars, 
Jupiter, Saturn, Uranus and Neptune - Ceres, currently considered an 
asteroid, and three "plutons," one of which is Pluto. 

The other plutons are Charon, currently described as a moon of Pluto, 
and the newly-discovered object 2003 UB313, which has not been named 
officially, but is nicknamed Xena. 

Ceres is the largest object in the asteroid belt between Mars and 
Jupiter, and like a planet is spherical in shape. 

A resolution to accept the new planet definition will be voted on by 
members of the International Astronomical Union (IAU) next Thursday, 
24 August. If passed, the days of simply learning the names of the 
nine planets will be over for the world's schoolchildren. In future, 
many more planets could join the Sun's family as other plutons are 
discovered. 

A dozen "candidate planets" are already on the IAUs "watchlist". They 
include Varuna, Quaor and Sedna, all Pluto-like objects residing 
within a region on the fringe of the Solar System known as the 
"Kuiper Belt". 

Plutons differ from classical planets in that they have orbits round 
the Sun that take longer than 200 years to complete, and their orbits 
are highly-tilted and non-circular. 

All these characteristics suggest that they have an origin different 
from that of classical planets. 

The IAU has taken two years working out the differences between planets 
and smaller Solar System bodies such as comets and asteroids. 

IAU president Professor Ron Ekers said: "Modern science provides much 
more knowledge than the simple fact that objects orbiting the Sun 
appear to move with respect to the background of fixed stars. 

"For example, recent new discoveries have been made of objects in the 
outer regions of our Solar System that have sizes comparable to and 
larger than Pluto. 

"These discoveries have rightfully called into question whether or not 
they should be considered as new 'planets'." 

According to the new draft definition, two conditions must be satisfied 
for an object to be called a "planet". 

First, the object must be in orbit around a star, while not itself 
being a star. Second, and most importantly, it must be massive enough 
for its own gravity to pull it into a nearly spherical shape. 

The IAU, responsible for the naming of planets and moons since 1919, 
set up a Planet Definition Committee (PDC) to consider the problem. 
Committee member Professor Richard Binzel said: "Our goal was to find a 
scientific basis for a new definition of planet, and we chose gravity 
as the determining factor. 

"Nature decides whether or not an object is a planet."

Mnemonic needed

IF ASTRONOMERS decide to change the number of planets in our solar 
system then piles of science textbooks will have to be rewritten. 

Generations of children have learned the names of the planets using 
mnemonics, listing the celestial bodies in their order from the Sun. 

"My Very Eager Mother Just Sent Us Nine Pies" is one popular aide 
memoir, helping students to remember Mercury, Venus, Earth, Mars, 
Jupiter, Saturn, Uranus, Neptune and Pluto. 

Other useful phrases include "Make Very Easy Mash - Just Squash Up 
New Potatoes" and "My Very Easy Method Just Showed Us Nine Planets".