Should we revoke Pluto's status as a planet?

[wilfulton]

Some controversy has arisen, and it will no doubt not get any better with the discovery of another "planetoid" that is larger than Pluto. Should Pluto's official "planet" status be revoked?

The underlying premise is that when discovered, Pluto was the ninth planet. Early measurements suggested that it was, in fact, about the same size of Mercury, although perhaps less massive. As telescope images improved, however, we discovered that not only was Pluto much smaller than we thought, but also that it has a moon, which is a good portion of its own mass. In addition, a number of other objects have more recently been discovered around the orbit of Pluto that were almost as big, and now we have discovered one that is even bigger.

Historical precendent holds that Ceres was once listed as a planet, before it was discovered to simply be the largest asteroid in the asteroid belt, one of many, and was in the past, demoted. Should

I vote that Pluto should keep its status, if only out of tradition's sake.

And I add that no matter which side of the fence you sit on, we live in a truly amazing universe!

[Alyeska]

Mercury and Pluto are different types of bodies in space. Mercury is definately a rocky developed planet with a stable orbit while Pluto is mostly made up of an ice rock combination and does not have a stable orbit. Unless we are going to list a 10th and 11th planet now, I think Pluto should loose its planetary status.

[Quadlok]

I say that any object in the solar sysytem massive enough to maintain a spherical shape and not orbiting a body other than the Sun should be considered a planet. Partially because I want to make the astrologists heads explode when there are three hundred planets to keep track of.

[RedImperator]

Pluto gets into the planet club on a legacy admission. I'ts obviously just a large Kupier Belt object, but it's been called a planet for decades now; it's too late to throw it out. Astronomers aren't under any obligation to do so, of course, but the as far as the public is concerned, the Solar System has nine planets.

[Solauren]

I think we need to really define what a planet is.

I mean, are we going to put a minimum size on it? Or a size/compisition requirement combination.

i.e: If all ice, must be at least 5000 kilometers across, otherwise it's a Cometiod?

[Enforcer Talen]

Id say cancel it. We've done it in the past.

[InnocentBystander]

Honestly, Pluto has been a planet for so long now, even if it's status were to be revoked, I'd still name it as one of them when asked.

[tharkûn]

I like the term "honorary planet".

[FSTargetDrone]

Establish a defintion for a planet. For example:

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

These statements are a compromise between definitions based purely on the deuterium-burning mass or on the formation mechanism, and as such do not fully satisfy anyone on the WGESP. However, the WGESP agrees that these statements constitute the basis for a reasonable working definition of a "planet" at this time. We can expect this definition to evolve as our knowledge improves.

If Pluto does not conform to this or some other internationally-recognized definiton, then remove it from the list of planets. Just because it's been called a planet for a long time shouldn't matter much if we want to be precise.

Definitions and names are important, especially in scientific areas...Is Australia a continent, or is it really just a big island? Sure, there are some Australians who call it the "world's biggest island" but what is it, by definition?

If we must keep Pluto on a list for some sentimental reason, call it a "planetoid" or whatever.

[Erik von Nein]

If it's defined out of it's position (like that of PSTagetDrone's) it should lose it's status.

[Darth Fanboy]

Does it's weird orbit that actually puts it closer to the Sun than Neptune at times have any bearing? Or am I wrong on that?

[LMSx]

Keep it, for inertia if for no other reason.

And I second Quadlok's plan.

[Asst. Asst. Lt. Cmdr. Smi]

Does it's weird orbit that actually puts it closer to the Sun than Neptune at times have any bearing? Or am I wrong on that?

I think during it's 200-something-year cycle around the sun, there's a 20-year period where Pluto's elliptical orbit makes it closer to the sun than Neptune.

[Lord Zentei]

I like the term "honorary planet".

Yup. Not an actual planet, per se, but it gets into the clubhouse.

[Gil Hamilton]

It's an "honorary planet" as far as I care, at the risk of offending the other Kuiper Belt Objects who aren't in the club. At the very least, it sounds better to say that you are sending a mission "to the furthest planet in the system" than "a Kuiper Belt Object" when you are trying to secure funding, even if the mission objectives are entirely identical, simply because calling it a planet makes it sound much more interesting. It's all in the way you sell it.

[Crossroads Inc.]

I like the term "honorary planet".

That works for me! Really it's all about the Orbits... Theres several obgects far bigger then PLuto that are 'Moons' instead of planets because the orbiting Saturn and Jupiter.

[HyperionX]

I suspect we will soon find a number of other Kuiper belt objects nearly as large or larger than Pluto. It'll soon be clear that Pluto is nothing but a lucky accident that a larger than average KBO was in the right place at the right time to be found. It's not a planet but rather a giant comet.

My opinion is that we define it as if some alien race came for a visit to our solar system and only what they would consider to be planets only we should consider as planets too.

[GrandMasterTerwynn]

I would say that one should consider an object a planet if it has the following characteristics (this is an idea that I pulled from my ass, but eh):

A) It is large enough to be round, yet not so large that it has taken up deuterium burning in its core. Some might suggest that it should be large enough to hold a permanent atmosphere. This would, however, eliminate Mercury, except that if Mercury were to have formed at the orbit of Mars, then it would easily hold onto an atmosphere of comparable thickness (its escape velocity is almost 90% that of Mars.)

B) It should orbit in the ecliptic plane of its solar system. In our case, the ecliptic is defined by the plane in which Earth orbits. Generically, it should be the plane in which the system's major planets orbit, or the plane defined by the primary star's equator. (In which case, the generic ecliptic should really be defined by Jupiter's orbit.) Some might say a planet's orbit should have a low eccentricity, but a fair number of the giant planets we've discovered have high orbital eccentricities.

C) It should not be in a region infested with dozens/hundreds/thousands of similar small bodies.

This system of classification would remove Pluto, since its orbital plane deviates substantially from the ecliptic, and it is indistinguishable from other Kuiper Belt objects. (When Ceres was discovered, it too was originally hailed to be a planet, being fairly large and in a circular orbit. The problem came when many other objects of similar size were discovered in the same general region. This lead to Ceres' demotion to that of just the first asteroid.)

Essentially, Pluto should be demoted from Planet #9 to where it properly belongs, as Kuiper Belt Object #1, and I'm fairly sure this will eventually happen, as we discover more, and more KBOs of similar size.

[Jalinth]

Essentially, Pluto should be demoted from Planet #9 to where it properly belongs, as Kuiper Belt Object #1, and I'm fairly sure this will eventually happen, as we discover more, and more KBOs of similar size.

I'd expect that the Solar System will continue to have 9 planets - astronomers might change their charts, but the public will keep using the 9 planet number for a very long time.

In any other solar system, Pluto would get relegated to an interesting KBO position - nothing more. But this is Terra after all. We can't be logical about our home.

[Noble Ire]

In any other solar system, Pluto would get relegated to an interesting KBO position - nothing more. But this is Terra after all. We can't be logical about our home.

For a species who calls its homeworld a synomym for dirt and terms its solar system's star and planet's only moon... as the Sun and Moon, having an honorary planet isnt too much of a strech.

I'm in favor of it.

[Surlethe]

I would say that one should consider an object a planet if it has the following characteristics (this is an idea that I pulled from my ass, but eh):

A) It is large enough to be round, yet not so large that it has taken up deuterium burning in its core. Some might suggest that it should be large enough to hold a permanent atmosphere. This would, however, eliminate Mercury, except that if Mercury were to have formed at the orbit of Mars, then it would easily hold onto an atmosphere of comparable thickness (its escape velocity is almost 90% that of Mars.)
<snip>

I like your initial criterion to define a planet: mass large enough for gravity to keep it together (rather than E&M), not big enough to fuse, and orbiting the system primary.

But, I say we reclassify the original 8 as "superplanets", let Pluto in as a club member, and define everything else as normal planets beyond asteroids and comets.

[Grandmaster Jogurt]

But, I say we reclassify the original 8 as "superplanets", let Pluto in as a club member, and define everything else as normal planets beyond asteroids and comets.

There's already a classification system similar to your idea of "superplanets and planets". The Major Planets are the Big 9, and the Minor Planets are the asteroids.

That being said, I think that Pluto and Ceres should share the same status as Major Planets or not. They both fit the first two of GMT's requirements, and were thought to fit the third for a time. Or maybe they can both by "honorary Major Planets".

[Surlethe]

But, I say we reclassify the original 8 as "superplanets", let Pluto in as a club member, and define everything else as normal planets beyond asteroids and comets.

There's already a classification system similar to your idea of "superplanets and planets". The Major Planets are the Big 9, and the Minor Planets are the asteroids.

I thought "minor planets" could be referred as "planetoids"; are those separate from "minor planets"?

[SoX]

My main arguements for Pluto to be rovked as a planet are, in no particular order, as follows:

1) Orbital inclination to the ecliptic is 17.14 degrees compared to the next highest, Mercury's of 7 degrees. This just make it look like a captured body, entered at a strange angle, probably not formed from the protoplanetary disk as this would have been pretty much in the same plane.

2) Why is Pluto not a gas giant, presuming all other 8 planets accreted during the formation of the solar system from the protoplanetary disk, why did Pluto not gather gas as Jupiter, Uranus and Neptune did?

3) Its mean distance from the sun is 39.5 AU, the Kuiper Belt extends from around 35AU to 50 AU then tapers off. Pluto is surrounded hudnreds, if not thousands, of similar objects.

They're pretty much the same as GrandMasterTerywnn's arguements.
Pluto was just not formed when all the other planets were, and not in the same way. It doesn't fit with the terrestrial planets, and it doesnt fit with the gas giants. It does, however, fit with the Kuiper Belt.

[SoX]

oh yeah, and my lecturer said we only gave Pluto planetary status as a favour to the Americans, since it was the only planet they'd discovered .... I think he had summat against American Astronomers....