What makes a planet? Pluto insights....

[Dr Mordrid]

Had a conversation today with astrophotographer John Chumack of Galactic Images (his company; published in Astronomy, Sky & Telescope, Time, Newsweek, National Geographic etc.) concerning the demotion of Pluto to a "minor planet". John has a very interesting take on that decision by the IAU.

First the criteria used by the IAU. A planet;

(1) is in orbit around the Sun.

(2) has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape.

(3) has cleared the neighborhood around its orbit.

Obviously Pluto qualifies as a planet under criteia 1 and 2.

According to the IAU the rub is criteria 3. They say that Pluto (2,306 km) has not "cleared its neighborhood". Presumably this is because the center of mass of Pluto and its moons, Charon (1,212 km), Hydra (45-60 km)& Nix (45 km), lay outside Plutos surface and a few small bodies from the Kuiper belt are near its orbit.

John makes two arguements against the IAU decision;

1. it's inconsistant. Using the "cleared the neighborhood" criteria Neptune should also not be a planet. This because Neptune has not "cleared" Pluto, Charon, Hydra or Nix from parts of its own orbit; all 4 bodies cross Neptunes orbit twice per cycle due to the Pluto systems eccentric orbit around the sun. Yes; Plutos orbit is more inclined, but still....

2. it was a political decision, as in anti-American. Pluto is the only planet discovered by an American and because of the overseas political environment this was a way to "get back" at the US by an overly PC IAU voting membership. He didn't say so, but I got the impression he heard this directly.

My 2 cents is that Venus, Earth and Mars also come very close to violating the "cleared the neighborhood" criteria, perhaps more so than Pluto, because the Apollo, Amor, Aten and other near Earth/other inner planet asteroids spend a lot of time in their orbits, quite often impacting.

John's information is that the number of American astronomers at the next IAU meeting will be far more than impressive

[az]

2. it was a political decision, as in anti-American.

HAHA! Hahahahaha! Ha! Right. Don't take yourselves too seriously.

John's information is that the number of American astronomers at the next IAU meeting will be far more than impressive

Everything is a war for you, and you even enjoy it, hmm?

[Jon P. Inghram]

Saying that classifying Pluto as a minor planet is "America bashing" is really a stretch. I really don't see the problem, it's not like they went and took it's name away and retcon'ed it out of existence, and as plus it also upgrades Ceres to the same level.

[Dr Mordrid]

II think you underestimate the degree of A/bashing that goes on in such circles. Guess you have to be there

[Brian Ellis]

HAHA! Hahahahaha! Ha! Right. Don't take yourselves too seriously.

Everything is a war for you, and you even enjoy it, hmm?

I agree with you 100%. When I read the OP, I nearly fell off my seat laughing. Does it matter two hoots who discovered any astronomical body and what nationality he/she is/was?

Perhaps the Hale-Bopp comet will be redesignated as not being a comet? And I suppose the 200,000 odd near-earth objects (asteroids etc.) discovered by the Lincoln Laboratory, MIT and NASA in the Linear project just simply don't exist, because Americans discovered them?

No international body would be as petty as Dr M suggests. They would be laughed out of existence for such conspiracy theories.

[Dr Mordrid]

No international body would be as petty as Dr M suggests. They would be laughed out of existence for such conspiracy theories.

Not petty? Pfffttt...

If an organization is made up of human beings it will take part in petty behavior. Period. Examples run from the UN, who has defined the standard for petty behavior, to every other organization that has set policies.

In case you hadn't noticed the IAU and its decision are already a source of ridicule and their credibility is in doubt over this issue, especially among astronomers themselves.

To show how screwed up this decision was; Owen Gingerich, chair of the IAU's planet definition committee, was denied his vote. The anti-Pluto crowd waited until he and 90% of the members attending had left Prague before calling another vote. Gingerich, an American, had helped author the IAU's original 12 planet definition.

Hmmmm....the American chair leaves and they stage a palace revolt. How petty

Of the total IAU membership, about 10,000, only 4% was able to vote.

This decision was not made with anything close to a consensus, much less a quorum, of the IAU membership at Prague. It's also the reason why Gingerich and many, many other astronomers are pushing for E-voting on such major matters of policy.

If the IAU's decision making process had not been perverted by petty behavior on the part of a minority why would such a move be necessary?

[Technoid]

II think you underestimate the degree of A/bashing that goes on in such circles. Guess you have to be there

As most of the aledged "A/bashing" it only exist in your mind, it's really hard to "be there"

[Greebe]

Pluto does not meet criteria #2, it's orbital path is more eliptical than circular.

This was another one of the arguements the IAU brought against it.

Of the total IAU membership, about 10,000, only 4% was able to vote.

True, not only was there nothing close to a consensus, but the vote took place on the very last day after most members had departed.

I agree with ya Doc, not per se an anti american sentiment, but an anti intelligent boo hoo we're going to do what we want anyway child like behaviour. It's quite interesting to see how people look down on one another, from the bottom rungs all the way to the top of the intellectual ladder. A person with a HS diploma will cut down the person who was a drop out, the person who has a Masters will cut down anyone with less, and at the top you have the true wack jobs looking down at them all. Now put them in a room together and what do you get alot of the time, some of the most ludicris child like bickering/tantrums the likes of which can only be seen on an unsupervised preschool playground.

This is why goverment policy on all levels is so bloody screwed up.

And is the reason I declined Mensa many years ago.

[KvHagedorn]

Whenever I hear of someone being in mensa, I immediately lose some measure of respect for them. It's such an utterly vain thing to seek such empty recognition of your IQ, especially then to flaunt it. I personally don't see it as necessary.. if you can't summarily dress down the type of person who looks down upon you as intellectually inferior, then maybe you are intellectually inferior.

[Jon P. Inghram]

Where do high IQ high school drop-outs fit in?

[Nowhere]

http://forums.murc.ws/showpost.php?p=598271&postcount=9

Apparently your friend missed the thing that by "cleared" IAU meant mostly that it governs its neighbourhood...

[Dr Mordrid]

Pluto does not meet criteria #2, it's orbital path is more eliptical than circular.

This was another one of the arguements the IAU brought against it.

And a disingenuous one. ALL planetary orbits are elliptical, with the sun sitting smack on one of the ellipses foci; AKA Kepler's 1st law of planetary motion. Astronomy 101.

What varies is the eccentricity (flattening) of the ellipse. If the IAU were going to eliminate a planet based on its eccentricity they would have to kick out Mercury as it has the most eccentric orbit of any planet, including Pluto.

[cjolley]

And a disingenuous one. ALL planetary orbits are elliptical, with the sun sitting smack on one of the ellipses foci; AKA Kepler's 1st law of planetary motion.

Astronomy 101.

Speaking of disingenuous.
The only planetary orbit that even comes close to being as eccentric as Pluto's is Mercury.
And It's 25 times as massive.

http://vathena.arc.nasa.gov/curric/space/planets/planorbi.html

This is all just a tempest in a teapot.

http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html

Pluto orbits beyond the orbit of Neptune (usually). It is much smaller than any of the official planets and now classified as a "dwarf planet". Pluto is smaller than seven of the solar system's moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton).

orbit: 5,913,520,000 km (39.5 AU) from the Sun (average)
diameter: 2274 km
mass: 1.27e22 kg

In Roman mythology, Pluto (Greek: Hades) is the god of the underworld. The planet received this name (after many other suggestions) perhaps because it's so far from the Sun that it is in perpetual darkness and perhaps because "PL" are the initials of Percival Lowell.

Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.

After the discovery of Pluto, it was quickly determined that Pluto was too small to account for the discrepancies in the orbits of the other planets. The search for Planet X continued but nothing was found. Nor is it likely that it ever will be: the discrepancies vanish if the mass of Neptune determined from the Voyager 2 encounter with Neptune is used. There is no Planet X. But that doesn't mean there aren't other objects out there, only that there isn't a relatively large and close one like Planet X was assumed to be. In fact, we now know that there are a very large number of small objects in the Kuiper Belt beyond the orbit of Neptune, some roughly the same size as Pluto.

...
There has recently been considerable controversy about the classification of Pluto. It was classified as the ninth planet shortly after its discovery and remained so for 75 years. But on 2006 Aug 24 the IAU decided on a new definition of "planet" which does not include Pluto. Pluto is now classified as a "dwarf planet", a class distict from "planet". While this may be controversial at first (and certainly causes confusion for the name of this website) it is my hope that this ends the essentially empty debate about Pluto's status so that we can get on with the real science of figuring out its physical nature and history.
...

(emphasis mine)

[dbdg]

I'm not really bothered about the distictionion of Pluto either way but I do have a question.

What if we discover some planets (may already have) that are 100 times larger then Jupiter, will we then classify them as Giant planets, if so that seems a little silly as we would end up with three types of planets.

Also what if out of the next 5000 planets we discover, they all have orbits like Pluto and not like Earth, how will that alter things?

[cjolley]

I'm not really bothered about the distictionion of Pluto either way but I do have a question.

What if we discover some planets (may already have) that are 100 times larger then Saturn, will we then classify them as Giant planets, if so that seems a little silly as we would end up with three types of planets.

Also what if out of the next 5000 planets we discover, they all have orbits like Pluto and not like Earth, how will that alter things?

3 types of planets bother you?
How do you feel about dog breeds!?

People classify things. That's just the way our minds work.