Pluto is now going to be decided, Planet or not !

[Sonia]

Pluto has been considered a planet since its discovery, but this position has come under threat with the discovery of 2003 UB313 (aka Xena), an object larger than Pluto orbiting out further in the Solar System. The International Astronomical Union will be meeting in August to decide on the fate of Pluto. By September, we could have 8 or 10 planets in the Solar System, but there won’t be 9 any more

At its conference this August, the International Astronomical Union (IAU) will make a decision that could see Pluto lose its status as a planet.

For the first time, the organisation will be officially defining the word “planet”, and it is causing much debate in the world of astronomy.

There is only one thing that everyone seems to agree on: there are no longer nine planets in the Solar System.

The debate has been brought to a head by the discovery of a potential 10th planet, temporarily named 2003 UB313 in January 2005. This new candidate planet is bigger than Pluto.

The question now facing the IAU is whether to make this new discovery a planet.

Pluto is an unusual planet as it is made predominantly of ice and is smaller even than the Earth’s Moon.

There is a group of astronomers that are arguing for an eight-planet Solar System, with neither Pluto or 2003 UB313 making the grade as a planet; but a number of astronomers are arguing for a more specific definition of a planet.

One of these; Kuiper Belt researcher Dr Marc Buie, of the Lowell Observatory in Arizona, has come up with a clear planetary definition he would like to see the IAU adopt.

I believe the definition of planet should be as simple as possible, so I’ve come up with two criteria,” he said.

“One is that it can’t be big enough to burn its own matter - that’s what a star does. On the small end, I think the boundary between a planet and not a planet should be, is the gravity of the object stronger than the strength of the material of the object? That’s a fancy way of saying is it round?”

This definition could lead to our Solar System having as many as 20 planets, including Pluto, 2003 UB313, and many objects that were previously classified as moons or asteroids.

One possible resolution to the debate is for new categories of planet to be introduced. Mercury, Venus, the Earth and Mars would be “rocky planets”. The gas-giants Jupiter, Saturn, Uranus and Neptune would be a second category.

Whatever the outcome of this debate there is only one thing that we can be certain of; by September 2006 there will no longer be just nine planets in our Solar System.

[toetoe]

Interesting stuff Sonia, to me, Pluto will always be a planet. :)

[Robert_T]

these sort of debates seem to arise in all branches of science at one point or other. we start with limited knowledge which appears to show big step differences between different "categories" or "types" of objects. as knowledge grows the voids between these types become uncomfortably full and the differences increasingly arbitrary. we could redefine and reclassify, The point is the terminology IS arbitrary in that it is simply imposed by ourselves as observers, the various rocky and gaseous things out there are blissfully unaware of our differentiation of them as planets, asteroids etc. people like to categorise, its in our nature, but if we want that categorisation to be more meaningful (that is useful for predicting how such objects came to be, interact with other objects etc) then the best categorisation is based on "behaviour" e.g. the way objects move and where, their makeup etc (I like the must be round bit as it covers formation), rather than rigid quantifiable criteria such as greater than 3000km diam...

anyway, just some thoughts

[slice of heaven]

Planets come and planets go.:)
This debate has been thrashed around for ages, the discovery of UB313 last year finally pushed it to a head where there were grounds enough to warrant a review of the term planet.
4 asteroids were originally classified as planets, then reduced to minor planet status later on. Ceres still qualifies as a planet by the current definition.:screwy::shrug: The number of planets has varied from 5 to 11 through the ages as our understanding of the solar system has changed. Things change.
The IAU stated they would assess it with regards to cultural, historical and scientific viewpoints.
Hopefully common sense prevails.

[Soldant]

I suppose they could label it a minor planet, but the fact remains that in the eyes of the public, it is Planet Pluto. Science can define it as whatever it likes, but that doesn't stop people from still regarding it a planet.

If they're going to base it on cultural and historical viewpoints, as well as scientific, then they're probably going to take a back seat because there's more to support it being called a Planet culturally and historically than scientifically (where it doesn't really stand a chance).

I don't like the idea of us having 20 planets. Imagine trying to get kids to rattle off the names of 20 planets. Besides, what are we going to call all the other planets?

[jjjnettie]

I think that we will have 8 Planets. Then maybe the others called KB1 Pluto, KB2 Xena etc for the Kuiper Belt objects.

[Argonavis]

Agreed. There are really only 8 planets. All the rest are minor planets, asteriods, planetismals, KBO's or TNO's.

Sorry Clyde T, but as consolation there will still be a special Chapter in every introductory Astronomy textbook noting your achievements.

It is now a matter to decide what a moon is, rather than have every pebble and rock found orbiting Jupiter and Saturn to get its own special name.