The IAU definition is absurd given the current search for exoplanets, because we will be able to detect planemos orbiting other stars long before we have any hope of being able to tell whether they've cleared their orbits. It would be much more practical - that is, useful for actually communicating empirical information - to define a planet as a planemo, Luna, Ceres and Eris included.

> The IAU definition is absurd given the current search for exoplanets, because we will be able to detect planemos orbiting other stars long before we have any hope of being able to tell whether they've cleared their orbits.

The IAU definition of “planet” explicitly applies only to the solar system, and the only definition even attempted for exoplanets IIRC is to try to define a dividing line between them and brown dwarfs, effectively “exoplanets” are extrasolar planemos.

> It would be much more practical - that is, useful for actually communicating empirical information - to define a planet as a planemo, Luna, Ceres and Eris included.

I don't see how that follows, since having cleared an orbit is addition empirical information, and information that we are able to develop on solar system objects, if not extrasolar ones, in reasonable time. As is, e.g., whether or not an object is a natural satellite of something orbitting the sun or does so itself.

> effectively “exoplanets” are extrasolar planemos

Right, which I think proves my point - surely we'd like planet and exoplanet to mean equivalent things.

> I don't see how that follows, since having cleared an orbit is addition empirical information, and information that we are able to develop on solar system objects, if not extrasolar ones, in reasonable time.

Well, I'd argue that Pluto (and Ceres before it) shows that it may take us an unreasonably long time. And the current definition awkwardly mixes two things that are really separate concerns: the characteristics of the object itself and what it's orbiting.

> It would be much more practical - that is, useful for actually communicating empirical information - to define a planet as a planemo, Luna, Ceres and Eris included.

I remember actual excitement among the layperson upon the announcement of discovering a 10th planet.

Now with "dwarf planets" no one cares.

Which is interesting since that would mean that "the nine planets" is a totally valid, understood concept, just like "the seven seas" - which is actually since a more interesting concept since that's a much more vague term since arguably the actual number of "seas" is anywhere between 1 (since basically all the worlds water is interconnected, bar a few endorheic basins) and "many", if you start counting large inland bodies like the great lakes that see substantial ship traffic.

My 2 year old daughter sings a song at nursery, that goes “there are 8 planets in the solar systems”.

Tempus fugit!

Every time Pluto is discussed as a planet, I remember that, according to IAU, Earth is not a planet. A planet is a celestial body, earth isn't.

Well, then actually on July 20th, 1969, the earth did become a planet, for at least some humans, and thus, by virtue of our capacity for taking the perspective of others, we may now all refer to it as such.

I sincerely hope to remember this when I'm drunk and need it.