Planets again

[mmcirvin]

...And now the AP says the IAU has gone in the less expansive direction, distinguishing between dwarf planets and real planets and demoting Pluto. I can't tell exactly from the article but it sounds as if there's a qualifier that excludes objects obviously part of a population of similar bodies in similar orbits.

(The article claims that Pluto is disqualified because its orbit "overlaps" Neptune's, but that can't be right without further detail, or it would disqualify Neptune too! I would think that Pluto is disqualified because it's one of a whole population of similar bodies in similar orbits, some of which are of comparable or even greater size.)

Comments

[james-nicoll.livejournal.com]

The current definition of planet does not seem to be able to distinguish between stars, brown dwarfs and the objects we previously called planets.

[doctroid.livejournal.com]

Hmm, I recall reading a day or so some proposed language along the lines of "... dominates the region around its orbit ..." or something vaguely like that. "Dominates" is the word I remember. With that language you could disqualify Pluto for crossing Neptune's orbit without disqualifying Neptune. But now the phrase seems to be "has cleared the neighborhood around its orbit", and, as you say, if that applies to Pluto, it applies likewise to Neptune.

[muffyjo]

http://www.cnn.com/2006/TECH/space/08/24/pluto.ap/index.html also talks about that.

[doctroid.livejournal.com]

It was unclear how Pluto's demotion might affect the mission of NASA's New Horizons spacecraft, which earlier this year began a 961/27-year journey to the oddball object to unearth more of its secrets.

Quick! Call it back!

Sheesh.

[doctroid.livejournal.com]

The IAU website is slashdotted, but according to Wikipedia, the text of the resolution as approved is as follows:

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

A "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) shape, and (c) has cleared the neighbourhood around its orbit.

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) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of Trans-Neptunian objects. All other objects, except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".

The first sentence isn't in Wikipedia's statement of the final resolution, but is in the final draft, and I suspect is really in the final resolution (or at least in the text accompanying the final resolution.) It explicitly punts on the applicability of the definition to extrasolar objects. Wisely so.

Looking at the full text, I can't see how Pluto's crossing of Neptune's orbit is relevant. Maybe the thinking is that Pluto didn't clean up its region of the solar system because Neptune did (and Neptune's failure to get rid of Pluto is too small an omission to worry about.)

[aderack.livejournal.com]

Whoa, big stuff is afoot.

I Have No Science Here, I Just Want To Say

[infrogmation.livejournal.com]

"TOFKATPP" The Object Formerly Known As The Planet Pluto

[ultraman.livejournal.com]

Why would they choose the name "dwarf planet" for the class of objects which are not planets?

"Dwarf" as a modifier usually doesn't undermine the attribute it modifies, but apparently it does in this case.

Dwarf stars are still stars, right?

BULLSHIT MR HAN MAN!

[timchuma.livejournal.com]

Everyone will just ignore this ruling and keep calling Pluto a planet anyway. The books won't be updated for decades. Does anyone even use astronomy textbooks now?

What about Uranus?

[timchuma.livejournal.com]

Did they wipe that too?

[paracelsvs.livejournal.com]

Why didn't the earlier suggestions just dump the overly complicated and confusing nonsense about barycenters, and just say "NO SATELLITES ALLOWED" like the new one? That would have gotten rid of the Pluton-Charon double planet, which I am sure was way too silly for too many people to allow it to stand.

Won't anybody think of the children?

[mmcirvin.livejournal.com]

...As for the popular reception, I think what the reaction all boils down to is a simple principle: By and large, people want their children to be taught in school the same things they were taught in school. This applies broadly across political lines, and it doesn't really matter what relation those things bear to reality. This is also why there's all the fuss over history education standards that don't focus on a Parade of Great American Heroes, evolution, the Pledge of Allegiance, etc.