If Pluto isn't a planet because its orbit overlaps Neptune's why doesn't that rule also disqualify Neptune?

Question

If the orbits of the two planets overlap and it's claimed that Pluto does not satisfy the new definition of a planet because it has not cleared Neptune from its orbit is it not also true that Neptune has not cleared Pluto from its orbit and therefore cannot be a planet. You cannot claim that the difference is that Neptune is already accepted as a planet whereas Pluto's status is the one in question because that is circular thinking and therefore unjustifiable.

Answer 1

No, that is not the reason.

From NASA:

"Here's how it all shakes out. The International Astronomical Union has decided that, to be called a planet, an object must have three traits. It must orbit the sun, be massive enough that its own gravity pulls it into a nearly round shape, and be dominant enough to clear away objects in its neighborhood.

To be admitted to the dwarf planet category, an object must have only two of those traits -- it must orbit the sun and have a nearly round shape. And no, moons don't count as dwarf planets. In addition to Pluto, Ceres and 2003 UB313, the astronomical union has a dozen potential dwarf planets on its watchlist."

So Pluto is one of many (perhaps millions) of "Pluto like object" that inhabit a part of the solar systen called "The Kuiper Belt" and Pluto is not even the largest of those objects, although it was the first to be discover. So Pluto is NOT dominant on his area.

Mike Brown, the discoverer of 2003 UB313, said:

"Pluto and 2003 UB313 are significantly smaller than the other planets. If you were to start to classify things in the solar system from scratch, with no preconceived notions about which things belong in which categories, you would likely come to only one conclusion. The four giant planets -- Jupiter, Saturn, Uranus, Neptune -- belong in one category, the four terrestrial planets -- Mercury, Venus, Earth, Mars -- belong in one category, and everything else belongs in one or maybe more categories. You wouldn't lump the largest asteroid -- Ceres -- in with the planets, you would group it with the other asteroids. Likewise you wouldn't group the largest object in the vast swarm of objects beyond Neptune (the "Kuiper belt") with anything other than the Kuiper belt. The previous nine (or ten) "planets" encompassed the group of giant planets and the group of terrestrial planets and then awkwardly ventured out into the Kuiper belt to take in one or two of the largest of those objects. Using the word in this way makes no scientific sense whatsoever."

and also said:

"I'm of course disappointed that Xena* will not be the tenth planet, but I definitely support the IAU in this difficult and courageous decision, It is scientifically the right thing to do, and is a great step forward in astronomy."

* As he (Brown) would like 2003 UB313 to be called but not its official name yet.

Are you still not convinced?

Then read this:

"What about Pluto crossing Neptune's orbit?

Partly this issue has come up from an incorrect statement in an AP wire story which says that Pluto is autmatically disqualified because it crosses the orbit of Neptune. Untrue. Pluto is disqualified because it is in the Kuiper belt but has not cleared out the Kuiper belt nor accumulated most of the mass in the asteroid belt, nor does it dominante the Kuiper belt. Pluto is part of a vast population and is rightly classified with that population where it belongs.
But surely this means Neptune has not cleared out Pluto and thus is not a planet, right? No. The problem here is simply with the hasty way in which the final definition was drafted, not with the concept, which is quite solid. And the concept is more important than a lawyerly reading of the definition. Neptune has a mass more than 8000 times greater than that of Pluto, and, in fact, totally dominates Pluto's region of the Kuiper belt. Much of the material in the Kuiper belt has indeed been tossed aside or accumulated by Neptune, but a very special region ("the Plutinos") have actually been captured by Neptune instead. We now know that Neptune formed much closer to the sun than where it was today, and, as Neptune moved out, it pushed these Plutinos out with it while forcing them into a peculariar orbit where they orbit the sun precisely twice for every three orbits of Neptune. Pluto is the largest of the Plutinos, and it and the others only exist where they do because of the dominance of Neptune. While a lawyer could make a case that Pluto has not been cleared by Neptune, the concept and intent of the definition is sound, and Neptune's total domination of Pluto's dynamics is actually an excellent demonstration of precisely the concept the definition is meant"

Answer 2

Frankly, I think your question is perfectly valid. The new defining characters for a "planet" have nothing to do with upon what plane a planet orbits the Sun, or whether Pluto is smaller that Neptune, or whether Pluto's orbit is "oddball" or more elliptical, or whatever:

"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."

Pluto is excluded as a planet because its orbit intersects that of Neptune; it has not cleared the neighborhood around its orbit. That's the ONLY reason. And by that very definition, Neptune cannot be a planet, either -- it hasn't cleared its orbit. If it *had* cleared its orbit, Pluto wouldn't be there.

Pretty straightforward, if you ask me. The new rules are dumb. Pluto may not be a planet, but the definition needs reworking. Those poor astronomers must've been tired at the end of that plenary session!

Answer 3

Pluto's orbit is highly irregular. Not only does it cross Neptune's orbit, but it orbits the sun at an angle to the normal orbital plane.

However, as I understand it, the main reason that Pluto was disqualified from planetary status is that it hasn't cleared its orbit of all other large objects the way the other 8 have. This is kind of specious as we have a huge asteroid belt between Mars and Jupiter. And, in fact, Jupiter alone has literally hundreds of large objects in its orbit that it tugs along with it as it circles the sun.

The eggheads in Prague have decided to call Pluto (& dozens of other objects in our solar system) "dwarf planets." I find this term to be bizarre and a bit confusing, seeing as these dwarf planets do not have to be small and they are not planets.

It seems to me that the smaller, denser planets like Earth & Mars have more in common with Pluto than they do with the gas giants like Jupiter & Saturn. Those planets are more like failed solar systems complete with moons that are the size of the Earth.

Anyhow, Pluto's status has nothing to do with Neptune.

Answer 4

Neptune doesn't have to clear Pluto because Pluto is way smaller than it. Pluto can't really say that about Neptune. Although if somebody could post the link to the exact rules as laid out by whatever 'International Status of Planets Comittee', that would be cool.

Answer 5

think about Neptune follow the same pattern as the other planets in orbit. Neptune is also a gas gaint and pluto is not as big as it is.
Pluto is also a part of other large objects in the far out solar system.

Answer 6

Neptune has a normal orbit like earth. It is almost round, on almost the same plane (I think thats what its called) of revloution as the earth. While Pluto for instance has a very tilted orbit. And also its orbit isnt much of a circle shape. Its an oval/egg shape. Plus its a very small planet (smaller than our moon!).

Answer 7

Becuase Neptune is in a typical orbital pattern for planets. One of the new rules is that you have to be in a typical orbital pattern for the solar system....or something like that. Neptune follows the typical pattern as the other planets. Whatever. Dumb rule. Pluto will always be a planet in my book.

Answer 8

If you look at a diagram of their orbits it will become quite obvious which one has the oddball orbit. Pluto does not even orbit on the same plane as the eight planets.

Answer 9

Because Pluto is too small. And because Pluto's orbit is very eccentric and inclined while Neptune's orbit is more like the other planet's orbits, hardly eccentric or inclined at all.

Answer 10

Neptune remains the largest object in it's orbit, that is the deciding factor.