Planets and Plutons - IAU Draft Definition

This is great fun - its generating a lot of comment on the Minor Planet (sorry, small solar system body) forum

Here's some more quotes:

re our Moon becoming a planet: For it to be a double planet, the center of gravity has to be in free space. The C of G of the Earth-Moon system is about 1000km inside the Earth.

Perhaps the Charon-Pluto centre of gravity is in free space hence Charon becoming a Planet (as part of a binary planetary system...)

Also, note that IAU have changed the voting rules:

"Keep in mind, though, that this is not official IAU policy until it is voted on by the IAU GA. Yesterday, there was a successful vote to change the rules of voting on scientific matters that will apply to this vote on the definition of planet. Previously, the vote was done by country, with each country having one vote done by the country representative. Now, the vote will be by IAU individual members, so all IAU individual members who are present at the GA next week will get a vote on the resolution defining planet."

Just like I don't like the term cubewanos or however you spell it!

Spelled correctly and you're right, a bit of an ugly name. It comes from the discovery designation of QB1 - similar objects found subsequently are called QB1o's.

As for the moon debate, presumably other moons in the solar system have a planet-moon c of g not in free space. e.g the Gallileans etc...

Oh yes, there is already of class object called 'Plutino'. With 'Pluton' in the mix, things may get confusing... As it happens...

From Wikipedia:
In geology, an intrusion is a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Bodies of magma that solidify underground before they reach the surface of the earth are called pluton

re our Moon becoming a planet: For it to be a double planet, the center of gravity has to be in free space. The C of G of the Earth-Moon system is about 1000km inside the Earth.

Perhaps I need a quick review of leaving cert physics but...

Since the moon's orbit is slowing down its getting further away. Since its getting further away the center of gravity of the system is going outwards. So will we have a scenario in a few million years whereby the moon suddenly switches from satellite to planet?

In fact since the earth is not a sphere we could have a period where the Moon would be a satellite when the cog passed through a mountain range, but a planet when the goc was over open sea

getting silly now...

I was more concerned with Oberon - what will happen when that passes very close to Uranus?

I'll get me coat...

How could Charon become a planet. It is orbiting already around a planet.
If a satelite becomes a planet...what happens then ... we end up with a whole lot of planets and no moons anymore ? That feels absurd... call me conventional but that is what I feel about it.

The IAU draft definition says an object is a planet if it is in hydrostatic equilibrium.

The Earth isn't quite at hydrostatic equilibrium as its oblateness is still in recovery from the loss of the more extensive ice caps of the last ice age. This is an observation from laser tracking of satellites and the observed rate of change is what would be expected in the circumstances.

No it says (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.

So you need enough mass to form to a hydrostatic equlibrium shape, which the Earth has. You don't need to be in perfect hydrostatic equilibrium.

You're just nitpicking about whats a minor surface anomily. But I think you're having fun nitpicking today