24 August 2006

Denver Post No Daily Planet

The print edition of the Denver Post this morning utterly screwed up their story on the status of Pluto and various other minor planets, something that Daily Planet would never have done. It said Charon was discovered in 1800s (that was Ceres). It said all three new proposed planets were plutons (again, something that doesn't apply to Ceres). For background see my earlier post on the subject.

Their updated story this morning has no such obvious errors. Now, according to the Denver Post, the call is for Pluto, Ceres and Xena to get dwarf planet status, and for Charon to remain classified as a moon of Pluto (implicitly treating the biggest object in a system as the primary, and everything else as a satellite). This will leave eight full fledged planets.

Pluto, Ceres and Xena are ruled out from the new rule, under which an object is a planet if it is:
"a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit." Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.
Ceres doesn't qualify under that definition because there are other objects in the asteroid belt. Xena doesn't qualify under that definition because there are lots of objects in its vicinity in the Kuniper Belt.

The final report direct from the IAU is found here. The official resolution states (formatting added):
IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation 'planets'. The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.

The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A "planet"1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

IAU Resolution: Pluto

The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
So, Pluto gets knocked down a notch, Ceres and Xena get promotions, and Charon gets knocked down a little by association with Pluto from satellite of a planet to satellite of a dwarf planet. As a consolation prize, Pluto and Xena and its friends will get a new name, but the IAU decided that the name "plutons" was not worthy. This is probably due to objections from geologists who already had dibs on that word.

When the dust settles in a few decades, there will be eight planets, several dozen dwarf planets, and lots of "small solar system bodies." Does that last name suck or what? Even the acronym, SSSBs sucks. Previous generations came up with names like asteroids and comets, and all we can come up with is SSSBs? Gah! The downsides of a lack of liberal arts education amongst astronmers is definitely making itself known.

UPDATE: What will be the political impact of this decision? Perhaps new ads like this one:
Bush loses City - NOLA
Bush loses Country - Iraq
Bush loses whole Planet! - Pluto
The term "dwarf planets" isn't that bad and while the prior term "minor planets" would have been better from the get go, it would cause confusion now since the same term would have two different definitions, a pre-2006 one and a post-2006 one.

The floor is open for anyone who would like to propose a replacement name for dwarf planets further out than Neptune most of the time, other than the previously proposed "plutons," and a better name for SSSBs.

1 comment:

Anonymous said...

I don't see anything wrong with Dwarf Planets, since the term is like Dwarf Stars. Unless it's not sufficiently politically correct, in which case they should be Little People Planets, or LiPPs.

But I agree, those SSSBs gotta go, and more than just the name. I think they should be called mustbedestroids, or MSBs, since they are PFTHP (pronounced like a raspberry), Potential Future Threats to Home Planet.