Interplanet Janet needs to get busy...

If you know who Interplanet Janet is, you're probably old!  In any case, that particular episode of Schoolhouse Rock is soon to become superceded by events.  On 24 August, the International Astronomy Union (IAU) will vote on a new definition of planet, and poor Janet will have a few more places to visit.

The new definition for planet that is proposed is as follows:

1. A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet.

2.  We distinguish between the eight classical planets discovered before 1900, which move in nearly circular orbits close to the ecliptic plane, and other planetary objects in orbit around the Sun. All of these other objects are smaller than Mercury. We recognize that Ceres is a planet by the above scientific definition. For historical reasons, one may choose to distinguish Ceres from the classical planets by referring to it as a “dwarf planet.”

3.  We recognize Pluto to be a planet by the above scientific definition, as are one or more recently discovered large Trans-Neptunian Objects. In contrast to the classical planets, these objects typically have highly inclined orbits with large eccentricities and orbital periods in excess of 200 years. We designate this category of planetary objects, of which Pluto is the prototype, as a new class that we call “plutons”.

4. All non-planet objects orbiting the Sun shall be referred to collectively as “Small Solar System Bodies”.

This definition for planet adds a few to the usual list that most of us grew up with.  For example, the largest asteroid (a misnomer, since asteroids are really planetoids, not little bits of star, but I digress), Ceres, becomes a planet under this definition.  Ceres had been considered a planet in the deep, historic past, and it looks like it has recovered its title.

Pluto becomes a planet, as does Charon and the object that some people want to call Xena.  These ice balls are the "plutons" noted in the quote.  The definition allows for a lot more plutons as our ability to observe the deepest depths of our solar system improves.

Notably excluded are the large moons, many of which are substantially larger than some of the planets under this definition.   There will be much arguing over the status of some moons I am sure.

So, the list of planets becomes (in the usual order from the Sun outward):

Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, 2003 UB313

Dover, DE (FP)
In a surprise move, lawers at Cheatem and Bilkem have filed a class action lawsuit on behalf of the Moon, Titan, Ganymede, Callisto, Io, Europa, Triton, Rhea, Iapetus, Dione, Tethys, Tritania, Oberon, Umbriel and Ariel at the International Court in The Hague.

“Our clients are being denied their rightful billing as planets,” said lead counsel Richard Visage, “and unfair billing is being distributed to smaller, insignificant objects in the outer rim.” It is believed that the plaintiffs are seeking status and punitive damages from the IAU.

When interviewed for comment, Mercury had this to say, “I don’t know what they’re on about. I’ve been a planet for a long time and it’s not all it’s cracked up to be. They named me after a naked man with wings on his feet… how do you live that down? Pass the sun screen please.”  Uranus added, "Feh.  Listen to Mercury... like he has it bad in the name department."

Ceres, traditionally quiet on the whole planet issue was more direct “4.5 billion years I floated out here, minding my own business. This lot, these ‘moons’ *HAD* to go float around Jupiter and Saturn or that icky Earth. Oh they were so cool back then. Now they’re ticked because they can’t be planets. They can kiss my asteroids. Patience paid off and I’m a planet now, so those bunch of moon rocks can go [expletive]. I made the big leagues and they’re just jealous. Here’s a moon for ‘em” [photo redacted]

Most of the plaintiffs were unreachable, but Io was adamant, “I got stuck here in the early days. I’ve been erupting crap for billions of years trying to blow this popsicle stand. Look, if that fat yellow blob in the middle didn’t hog up all the mass when we were young, I might be orbiting a star in my own right. I’m bigger and sexier than Pluto and Quaor. People look at me all the time, nobody sees those other two. Now if you’ll excuse me, I have to have an eruption.”

Lawyers for the IAU have not had time to review the court filing and had no comment at this time.

(P.S. Thanks to Ronn over at Bad Astronomy for reminding me about Uranus.  I'd forgotten about it when I originally posted the lawyer thing!)