Space Debate:- Reshaping the Final Frontier?

Question

This week sees the International Astronomical Societies gathering to discuss, amongst other things the definition of a Planet.

For Centuries, the definition has stood that it is a Celestial body in
orbit around a star, which is held by that stars Gravity. It also has
to be above a certain size, and a certain mass.

This definition has stood since the time there was 5 Planets (7 was an important number in ancient times, they counted the Sun and moon). Then along Came a dude called William Herschel who found Uranus, and then Neptune and Pluto were discovered. Then in 2005, Xena was added, and now we have planets breeding like Maggots.

This gathering this week could see that whole definition change. Pluto could loose its planetry Status, or it could be joined by Charron, Xena, and a menagerie of others in the Kuiper belt.

So, 2 questions:
What do YOU think makes a planet?
What is your opinion on the outer candidates?

No time limit for your thoughts?

You can substitute Maggots for anything that there could be lots of. Rabbits is a bit overused now, dont we think? ;-)

Just to clarify, though I know there is no scientific definition of a planet (That is the whole point of this meeting in Prague today), I went for the Oxford English definition, to quote:
"(n) A Celestial body moving in an elliptical orbit round a star. from the Greek for 'Wanderer'".

I am so dissappointed, Pluto has lost its full fledged planetry Status, giving us just 8 planets in our system and a selection of "Outer Dwarfes" or whatever they were called in the end.

I wanted Pluto to remain, with Charron as its moon, and Xena and Ceres, but obviously others feel different.

Now, I wonder when the new wall charts will come out.

Answer 1

I think there should be a definition of it being predominantly round in shape and of a certain size, otherwise we'll end up with every rock out there being classed as a planet and not enough space in the text books for the pretty Solar System diagrams! There should also probably be a maximum distance from the Sun.

Answer 2

Actually, you are wrong that there was an accepted definition of a planet for centuries. And even the working definition could never have been a celestial body in orbit around a star because this would make asteroids and comets into planets. And qualifying this with mass does not work because to do that you still have to promote some asteroids and demote Pluto. You also have the issue that some moons are larger than planets, and are also in orbit around the Sun (even though that orbit is modified by the planet that they also orbit).

So we were overdue some clarity.

However, I am not sure we got it. What we have is a fudge in order to preserve Pluto as a planet for senitmental reasons without littering the solar system with hundreds of minor planets in the form of large asteroids.

In reality, for our Solar system I think the distinctions are quite clear. There are four inner planets that are unambiguous - Mercury, Venus, Earth and Mars. There are then four gas giants - Saturn, Jupiter, Uranus and Neptune. Everything else is space rubble.

Answer 3

I mentioned this definition sourced from the Internet before the IAU conference began in my Yahoo 360 blog on 16th August:

Although there is no set scientific definition for planet (from the Greek planetes “wanderers”), as a rule of thumb, a planet: 1) must directly orbit a star or an object that has nuclear fusion; 2) must be small enough that it has not undergone internal nuclear fusion (ie, it is not a star or starlike object); and 3) must be large enough that its self-gravity gives it the general shape of a sphere.

In my opinion this definition should stand and it's very close to the one first put forward by the IAU at the beginning of the conference. That means Pluto, Charon, 2003UB313 will get planet status along with Ceres the asteroid planet. I'm happy with that. It may mean that we end up with thousands of planets. I don't think that's a big deal to worry about. Astronomy is a subject with rapidly changing knowledge and we must be prepared to move along with the times. We might end up with thousands but people for generations to come are always going to remember the first nine. I'm sure of it.

Sadly the IAU voted otherwise.

Answer 4

I'm hoping the Pluton model will emerge triumphant; if Pluto keeps its title as a planet, then the other, larger, plutonic worlds like Sedna and Xena can also be givne the status of planets.

The only real criteria should be that the body must be spheroidal, and that it orbit the Sun directly rather than a larger celestial body, such as the moons of Jupiter or Saturn.

If we sent out a probe to Pluto and found it to be a big, ugly spud and not a round ball as we think it could be, then we could probably drop the label "planet" if we wish; but even to consider the thought now, without further investigation, is an insult to the memory of the late Clyde Tombaugh, the little astronomer who found Pluto in 1930 in the first place.

Answer 5

Maggots don't actually breed ;-)

I think that the current definition should be slightly refined - it should be a celestial body in orbit around a star and not in itself in orbit around another planet (this would be a moon), and it should have a minimum size and mass, probably around the size of our moon. Perhaps there should be a new category of star-orbiting body for the likes of Pluto and Xena, such as planetoid.

Answer 6

I posted this ages ago....

I have a theory that the planets are shaped from chunks of rock and other space debris that get caught in the sun's orbit and are fused and globed by the imense heat. Once formed their mass becomes to heavy to sustain an orbit and makes them slowly spiral away from the sun and into space.
Scientist say there are creaters where oceans could of existed on Mars, so whats to say Mars once orbited the sun where earth now orbits and then in a few billion years, venus will be full of life?