IAU Proposes 3 New Planets

IZ Reloaded writes "Sources tell SPACE.com that the International Astronomical Union is preparing to include three new entries to the current list of planets in our solar system. From the article: The asteroid Ceres, which is round, would be recast as a dwarf planet in the new scheme. Pluto would remain a planet and its moon Charon would be reclassified as a planet. Both would be called "plutons," however, to distinguish them from the eight "classical" planets. A far-out Pluto-sized object known as 2003 UB313 would also be called a pluton."

Comments

One issue

[Kranfer]

As I concurrently submitted this I had to put in my 2 cents... By the article here If you use the new definition proposed... there would be up to 53 known planets in this Star System... Quite a lot of them to remember. Also by the definition since Charon would be a planet... wouldn't the moon need to be its own planet? And the 9580723409875 moons of Staurn/Jupiter etc? I think this will go back to the drawing board eventually.

Re:One issue

[mysticgoat]

Also by the definition since Charon would be a planet... wouldn't the moon need to be its own planet?

The Moon should be considered a planet: Earth - Moon functions as a double planet (barycenter far removed from the center of mass of either one; orbits of either one around the Sun are significantly distorted by the other; impossible to understand the features and history of either without taking into account the tidal influence caused by the other).

And the 9580723409875 moons of Staurn/Jupiter etc?

None of the above logic applies to these other cases. These satellites have no significant effect on their primaries.

I'm pretty sure that once it is generally recognized that the Earth - Moon is a double planet, we'll see some insights into plate tectonics and biological history that are currently out of scope.

Interesting solution

[andrewman327]

This is an interesting approach, though I am not sure why they even bother with the definition of planet anymore. Just consider Plutons as their own thing. I wonder if elementary students will now have to recite all 12 planets.

Here are the three additions:
*The asteroid Ceres, which is round, would be recast as a dwarf planet in the new scheme.
*Pluto would remain a planet and its moon Charon would be reclassified as a planet. Both would be called "plutons," however, to distinguish them from the eight "classical" planets.
*A far-out Pluto-sized object known as 2003 UB313 would also be called a pluton.

Sheesh

[wanerious]

The way I teach it in my classes is that there are 4 inner planets, 4 outer planets, and a (large) set of Kuiper Belt objects, of which Pluto is one of the largest and closest members. Why do we need a planetary definition? Historically, any serious attempt to classify natural objects eventually runs into problems anyway, especially when our first attempt includes objects that obviously belong to a number of sub-classes, each of which contains a continuum of members.

Rocheworld

[Rob Carr]

So how would this definition handle a Rocheworld, like in the book by that name by Robert L. Forward?

I like this defintion

[9x320]

Planet: A celestial object orbiting a star that is massive enough for its own gravity to warp itself into a nearly round, spherical shape. A planet may not be massive enough to initiate thermonuclear fusion. In order for a pair of celestial objects to be considered a double planet, in addition to meeting the forementioned criteria, the barycenter of both objects must be located above their surfaces. Planetary systems orbit a barycenter, or their center of mass. Usually that center of mass is located at the center of the planet, but in the case of Pluto, the gravity of its "moons" pull the barycenter above the surface. As a result, Pluto is perpetually orbiting the center of mass of the planetary system, as illustrated in a chart located in the Wikipedia article. This is why Charon and Pluto are being considered double planets. I think that's the best set of criteria that can be offered. Why is the idea of over 50 planets so abhorent? Why must size and the number of planets be decided arbitrarily? We might as well use Isaac Asimov's mesoplanet suggestion, in which all objects with radii between Ceres and Mercury are mesoplanets, if this is how it is to be decided.

Re:I like this defintion

[elrous0]

Why is the idea of over 50 planets so abhorent?

The short answer is that popular science (of the general public variety) is conservative and very slow to accept change. Something as radical as "Throw out everything you learned about 'the planets' in grade school, you ignorant hayseed!" is going to be met with popular resistance (not to mention resistance from grade school teachers who are all-too-often loathe to learn ANYTHING new). Anything that adds MORE complexity to science for people who can barely grasp even the BASIC principles they've already been given is not going to be greeted with "YEA! What a great opportunity to learn more!" in many places outside of /. and similar forums.

Hell, I live in a country that's still getting used to the idea of "evolution" almost 150 years later.

-Eric

Re:I like this defintion

[radtea]

Planet: A celestial object orbiting a star that is massive enough for its own gravity to warp itself into a nearly round, spherical shape...

The question is, why use the word "planet" for this class of bodies, when the definition is completely unrelated to the classical term?

Historically, a "planet" was a body that had three unrelated properties:

1) It orbits the Sun
2) It is far enough from the Earth to not show a disc and not have any visible moons
3) It is large enough to be visible from the Earth without too much trouble

These are the things that were called planets up until recently. With the invention of the telescope we got a couple of new ones, but apart from Pluto they were so similar to the other gas giants in the outer solar system as to be obviously classifiable in the same way.

But these properties have no interest to the scientific community, which is more interested in planetary formation and current planetary physics than how far things are from Earth. If any planet had had a visible moon or was close enough to show a visible disk for part of the year, for example, we might not have arrived at the concept of "planet" in the first place, but come up with some other sort of classification scheme for celistial bodies.

As such, "planet" is an arbitrary historical term that has as much place in the scientific lexicon as phlogiston or caloric.

The problem with 'plutons'

[Stavr0]

That's already how Pluto is spelled in French. I guess we could refer to small-p plutons for Pluto, Charon and Kuyper objects. And of course 'Pluton', being the eponymous pluton.

The actual definition

[Daetrin]

From the article: "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."

I guess the center of rotation of the Pluto-Charon system is actually above the surface of Pluto, making it a double-planet system? So far so good.

The bit about plutons and dwarf planets is a _lot_ less clear however.

"The IAU proposal suggests (but does not require) that these be called dwarf planets. Pluto could also be considered a dwarf, which the IAU recommends as an informal label.

So to recap: Pluto would be a planet and a pluton and also a dwarf."

So we've gone from the term planet being an indistinct label that we apply to whatever we happen to think deserves it to it being an exact definiton, but added _two_ new indistinct labels that we apply to whatever we happen to think deserves it. To me this doesn't seem like a great deal of improvement.

At least i'm not the only one who thinks this is a bit foobared:

"Boss was bothered by the lack of definitiveness on this and other points.

Boss, along with Stern, was on an IAU committee of astronomers that failed to agree on a definition. After a year, the IAU disbanded that committee and formed the new one, which included the author Dava Sobel in an effort to bring new ideas to the process.

Boss called their proposal "creative" and "detailed" but said it does not hang together as a cohesive argument."

I think whatever definition they finally settle on should be a usefull one once we actually start traveling between solar systems (wishfull thinking.) If we were just coming across the Sol system for the first time we would probably be concerned about the 8 major planets as places for potential habitation, convenient gravity wells and sources of resources. We might care about Pluto and Charon, but i doubt it would be for any practical purpose. We almost certainly wouldn't care about the 20-50 other planets this new definition would add other than as a curiosity.

I'm not sure if there's an easy way to clearly differentiate between the two, but there really ought to be at least two clearly distinct categories, "major planets" and "minor planets" or "planets" and "planetoids" or "dwarf planets."

Re:That's no moon

[Crayon Kid]

I thought Earth+Moon was also considered a "binary planet" thing, due to the rather extraordinary size of the Moon (for a satellite).

Not so sure this will go over well at all

[fade-in]

So, what does the Astrologer's Union think of all of this?