Number of Planets in Solar System

[neill]

Hi all,

Here's a poll for you - how many planets do you think there are in the solar system?

[Administrator]

As has been mentioned before on the forum, it's just semantics. If we take the original greek meaning of 'wandering stars' then we have to admit that there are more than 9.

The IAU is basically arguing over language, which shouldn't really be its concern. They need to give up on the term 'planet' altogether as it confusing matters, and is utterly meaningless to astronomy.

There are stars, which are objects that fuse matter in their cores and there are gaseous objects that do not fuse matter in their cores. There are also 'rocky' bodies, some of which are round and contain large amounts of silicon, carbon and iron. etc.

So what does the IAU describe as a 'planet'? well.

(i) is in orbit around a star or stellar remnants;
(ii) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape;
(iii) is not massive enough to initiate thermonuclear fusion of deuterium in its core; and,
(iv) has cleared the neighbourhood around its orbit.

Does anyone else think that the term is now overloaded?

Why does the neighbourhood have to be cleared? What exactly does 'cleared' mean? Why does a planet have to be in orbit? What do you call an object which is not in an orbit and has been ejected in some way from its stellar system? A free planet? "Nearly round" what kind of scientific terminology is that?