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."

Cowboy neal option

[LiquidCoooled (634315)]

How long until we can get Cowboy Neal reclassified as a pluton?

In other news...

[Chapter80 (926879)]

In other news, Ceres is being renamed Mickey, Charon is being renamed Daffy, and Disney/Pixar has a new movie coming out with the clever name of "2003 UB313".

Corporate sponsorship is running rampant... how did they get naming rights to the 9th planet in the first place?

Interesting solution

[andrewman327 (635952)]

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.

Re:Interesting solution

[andrewman327 (635952)]

The three bullet points in the parent are quoted from TFA [space.com]. The cite was cut off, apologies.

I hope there isn't life on 2003UB313 (which is very highly unlikely) because then we would have to talk about the 2003UB313ians and that would just be annoying.

Re:Interesting solution

[houghi (78078)]

I for one will already welcome our 2003UB313ian overlords.

Re:Interesting solution

[Citizen of Earth (569446)]

because then we would have to talk about the 2003UB313ians and that would just be annoying.

I think they'd be called "Warrior Princesses".

In another news...

[Cyberax (705495)]

Pluton politely asks media corporation not to use His name as a generic noun.

Sheesh

[wanerious (712877)]

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.

Re:Sheesh

[plasmana (984377)]

We need a planetary definition so we can communicate efficiently. Why else do we need words. Try talking about your environment without classifications of natural objects:

I bought my direct ancestral animated entities an animated entity with four appendages used for walking, one appendage for knocking down lamps, a soft covering that is white with black spots, which speaks in guttural exclamations which are just nonsensical to animated entities like myself.

Instead of:

I bought my kids a dog

As our observations of our environment reveals new information. We must periodically change our definitions to attempt to make our abstractions best reflect reality.

Yikes.

[Rob T Firefly (844560)]

Somewhere, Space Fonzie is jumping over an Astro-Shark.

I like this defintion

[9x320 (987156)]

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

[anshil (302405)]

"Why is the idea of over 50 planets so abhorent?"

Think of the complexity of the new astrology that would be needed to cater for 50 planets that then influence our fortunes, I would like my destiny be determined by just 9 planets...

Re:I like this defintion

[elrous0 (869638)]

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 g

Re:I like this defintion

[9x320 (987156)]

There are already 88 constellations with arbitrary, zigzagging boundaries between them used by the International Astronomical Union for classifying stars. Considering that two methods of naming stars uses the genitive Latin form of that constellation's name, the Latin genitive form must be memorized as well.

The best method of memorization for me was to construct a table with the constellation name in one column and the Latin genitive form in the other. Considering this, if there were 53 planets, for the pur

Why this is a wrong criteria

[YA_Python_dev (885173)]

Sorry to reply to myself, but I have found a good example: 2003 EL61 [wikipedia.org] has a much bigger mass than both Charon [wikipedia.org] and Ceres [wikipedia.org] but its shape is clearly not round: 1960×1520×1000 km!

The problem with 'plutons'

[Stavr0 (35032)]

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.

I don't care what they are named....

[lbmouse (473316)]

....what do they smell like?

Fry: Did you build the Smellescope?
Farnsworth: No, I remembered that I'd built one last year. Go ahead, try it. You'll find that every heavenly body has its own particular scent. Here, I'll point it at Jupiter.
[Fry sniffs.]
Fry: Smells like strawberries.
Farnsworth: Exactly! And now Saturn.
[Fry sniffs.]
Fry: Pine needles. Oh, man, this is great! Hey, as long as you don't make me smell Uranus.
[Fry laughs.]
Leela: I don't get it.
Farnsworth: I'm sorry, Fry, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all.
Fry: Oh. What's it called now?
Farnsworth: Urectum. Here, let me locate it for you.

Ah, memories...

[pjt48108 (321212)]

When they discovered that Uranus had rings, like Saturn, I was so excited that I ran out the front door and announced it VERY loudly to my little brother, at the far end of the driveway, by saying something along these lines: "Hey, they discovered that Uranus has rings!"

It was a classic example of realizing, only too late, that something might have been phrased much differently, or, perhaps, privately...

Re:I don't care what they are named....

[Andy_R (114137)]

This joke appeared on he UK tv show "Spitting Image" in the late 1980s, around the time the astronomical community was actually trying to get us to pronounce it 'ooranus' as opposed you 'your-anus'.

A newscaster (Sir Alistair Campbell if memory serves me correctly) was shown announcing the name change to "boo-mo-lay', followed after a second or so by a picture of the planet, captioned "Bumhole".

I laughed a lot... but in my defence I was about 13 years old at the time.

The actual definition

[Daetrin (576516)]

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."

Planetary Categories

[Rob Carr (780861)]

New Scientist has the complete set of proposed categories [newscientistspace.com] for planets:

• Planet: A round thing orbiting a star. More precisely, according to the draft definition: "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."
• Pluton: A planet orbiting beyond Neptune, taking more than 200 Earth years to circle the Sun. So far, it would include Pluto; Pluto's former moon, Charon; and "Xena" (2003 UB313).
• Satellite: Anything orbiting a planet, as long as the mutual centre of gravity does not fall outside the planet. Includes several bodies much larger than many planets, such as Jupiter's moon Ganymede (diameter: 5262 kilometres).
• Small solar system body: Anything orbiting the Sun that's not a planet or a satellite. Most asteroids and comets would be SSSBs. Currently called minor planets.

Unofficial categories of planet:

• Dwarf planet: A planet smaller than Mercury (diameter: 4879 kilometres), which is the smallest uncontested planet. Would include the former asteroid Ceres; Pluto; Charon; and Xena.
• Giant planet: Jupiter, Saturn, Uranus, Neptune.
• Classical planet: The four giant planets plus the familiar four rocky, terrestrial planets: Mercury, Venus, Earth, Mars.

The good side

[4D6963 (933028)]

Let's see the good side of things, maybe Ceres with its new status will gain some more interest, *maybe* even enough for it to have the honour to be probed by us. Would surprise me a bit tho.

Edit : seems that there's already a probe destinated to Ceres (among others) nammed Dawn [space.com]

Edit #2 : yeah I know, you can't actually edit your posts

Mike Brown's take on this

[call -151 (230520)]

Mike Brown, leader of teams that have discovered 2003UB313 and 11 other objects that meet the proposed definition of planet, has the following on his webpage [caltech.edu] now:

The IAU proposal officially recognizes only 12 planets; where does the number 53 come from?

By the proposed IAU definition, anything large enough to be pulled by its own gravity into the shape of a sphere and which is in orbit around a star is a planet. The proposal officially recognizes 12 planets (the nine previously recognized plus Ceres and Pluto's moon Charon plus 2003 UB313) creates a complex committee procedure for an object to become officially recognized. This part of the proposal is perhaps the weakest. In no other area of astronomy is there a definition for a class of objects and then a committee that has to decide if an object fits the definition. There are simply definitions. If an object fits the definition it is part of the class. If the IAU proposal is accepted then scientifically all of the spherical objects out there are indeed classified as planets, regardless of how long it takes for a committee to officiailly declare them to be so.

A relatively simple analysis show that there are currently 53 known objects in the solar system which are likely round. Another few hundred will likely be discovered in the relatively near future. Regardless of what the official count is from the IAU proposal these object all fit the scientific definition of the word planet and if the scientific definition is to have any credibility they should all generally be considered planets.

What should the public think about 53 planets?

Most people, when first confronted with a proposal to make 44 new planets in the solar system, seem to react by looking blankly for a second, then shaking their heads and muttering something about astronomers being crazy. Astronomers are not actually crazy, at least most of them. Astronomers have needed a good scientific definition of the word "planet" for many years now and this one works well for scientists. It doesn't, however, work terribly well for the rest of the world. The solution is the one that should have happened long ago: a divorce of the scientific term "planet" for the cultural term "planet." No one expects school children to name the 53 planets (most, in fact, don't even have names). If I were a school teacher I would teach 8, or 9, or perhaps 10 planets and then say "scientists consider many more things to be planets too" and use that opportunity to talk about how much more there is in the solar system. But at the end of the day I would talk about 8 or 9 or 10. Not 53.

Culture and science have always meant something different when they use the word planet, and with this new scientific definition so clearly far removed from what the rest of the world things a planet is there will no longer be any need to confuse the scientific word with the cultural one.

How am I going to vote on the IAU resolution?

This one is easy to answer. I am not an IAU member, I took no part in drafting the resolution, and I get no vote. If I were to vote, however, I would have to decide that while the definition itself is viable the extra non-scientific beauracratic barrage attached to the resolution would doom it for me.

Obscure classic rock joke

[BrynM (217883)]

The sun shines
And Pluto orbits
The spray flies as the comet glides
And planets orbit, orbits they're hiding
The IAU smile
And Pluto orbits
The system packs as the commity tracks
And planets orbit, orbits they're hiding

Behind an Astronomers front
Astronomers front - it's a pluton

(to the tune of Eminence Front by The Who - don't ask me why this song jumped into my head while reading the article)

To quote a local morning radio show

[cvd6262 (180823)]

This was covered on the local version of KBBL [wikipedia.org], and the commentary was spot on:

"These guys are in serious need of a girlfriend."

How about this one?

[tillerman35 (763054)]

Orbjects: noun. contraction of ORBiting oBJECTS (with the repeated B collapsed to a single character). Any object in a solar system that orbits. Focus of such orbit must be another object or center of gravity derived from two or more objects.

Further classification:
Little Orbjects: Wee orbjects that require only a passing flock of waterfowl to achieve escape velocity. Can only contain volcanos, sheep, roses, and possibly a child, tippler, king, or accountant.
Big Orbjects: Orbjects that would require an actual propulsion system including significant amount of reaction mass to achieve escape velocity.
Huge Orbjects: Orbjects whose mass is so great that a human being could not survive its gravitational pull. Or better stated, orbjects that you might have sex with, but wouldn't introduce to your friends.

Slight modification

[phlegmofdiscontent (459470)]

The term "dwarf planet" is actually starting to grow on me. It still keeps Pluto as a planet, for those who absolutely need it to be a planet, but really it IS a demotion to a status equal to the larger asteroids & KBOs. The way I see it, the Solar System has 8 Major Planets (4 terrestrial, 4 gas giants), at least 50 Dwarf Planets (Pluto, Ceres, 2003 UB313, etc) that are round due to self-gravitation, and the non-round objects can still be called Minor Planets. It just adds an intermediate classification between "planet" and "asteroid/minor planet".

Re:One issue

[goober (120298)]

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

Charon differs from Luna because Pluto and Charon jointly orbit around a point outside either of their bodies, whereas Luna orbits a point inside the Earth. Pluto and Charon are therefore (currently) technically a twin planet system.

Rocheworld

[Rob Carr (780861)]

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

Re:Rocheworld

[Agripa (139780)]

In short, it does not but only because Rocheworld is an extreme case.

They use the term sphere in the definition but that is the ideal where the planet is not influenced by outside gravitational force. Even the moon distorts the earth into a non spherical shape although it is cyclic since the earth is not tidally locked to the moon. The Rocheworld was tidally locked and the shape followed (please excuse me if I get the term wrong) an equalpotential curve of the graviational force which imo is what they rea

Re:One issue

[geobeck (924637)]

But according to an article by Isaac Asimov (Just Mooning Around from Of Time and Space and Other Things), the Sun pulls the Moon twice as strongly as the Earth does, and the Moon's orbit, drawn to scale, is always concave toward the Sun, making a very convincing argument that the Earth and the Moon are a double planet system, even though their center of revolution is a thousand miles beneath the Earth's surface.

If Charon is to be classified as a minor planet, the Moon should be too.

Re:One issue

[mysticgoat (582871)]

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?

N

Re:One issue

[WCMI92 (592436)]

The center of gravity between the Earth and Moon is inside Earth, true, but it's not at Earth's center... The moon is exceptionally large compared to the Earth, and affects Earth far more than if it were orbiting a gas giant.

BTW, isn't the Earth gradually losing the moon? I think I remember reading that the Moon moves away from Earth a few inches a year.

That's no moon

[Namarrgon (105036)]

It's a b... I mean, it's actually part of a double-planet system, orbiting around a common point in space (unlike all other moons in our solar system). And Ceres is an asteroid with a name, thank you very much.

In answer to your second question, since August 24, if the vote passes.

Re:That's no moon

[john83 (923470)]

All two body systems orbit a common point. If you cleared all the other gunk out of the solar system, the earth and the sun would orbit a common point. It would just happen to be very, very deep in the sun because of the disparity of mass. I don't see your argument there, unless you're saying that the common point is outside Pluto and that this isn't true of other systems.

Re:That's no moon

[isorox (205688)]

unless you're saying that the common point is outside Pluto and that this isn't true of other systems.

That's exactly what he's saying

Re:That's no moon

[mrxak (727974)]

Look at these animations [wikipedia.org]. Second from the left is Pluto and Charon. That's why they're both planets. The definition being proposed is rather elegant, I think. It leaves it up to gravity to determine what a planet is, and catches special cases like Pluto and Ceres rather nicely too. You have your 8 classical planets in nice orbits, you have your N plutons in crazy orbits, and you have your really small dwarf planets like Ceres that never quite made it.

Re:That's no moon

[Crayon Kid (700279)]

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

Re:That's no moon

[SpryGuy (206254)]

Actually, it's more due to the fact that in its orbit around the earth and around the sun, the moon is NEVER falling AWAY from the Sun. It always falls towards it.

It seems to me that might be a useful definition to consider... and it would make more sense for the Moon to also be classified as a planet, than for Charon (for example) to be classified as a planet while the moon (many times larger) isn't.

Frankly, though, I think the whole thing is a mess. Pluto, Charon, Quoar, Xena, and all the rest, are Kuiper Belt Objects, just like Ceres is an asteroid. In particular, Pluto, Charon, Quoar, Xena, and the others KBOs are all in highly elliptical orbits, outside the plane of the ecliptic. Why can't the definition of a planet include the plane of the ecliptic? We'd have 8 planets, and then a mess of KBOs.

Re:That's no moon

[dastrike (458983)]

While there is no absolutely firm definition of what constitutes a double planet (binary planet), one of the fairly widely accepted criteria is that the barycentre (the common point around which both of the objects orbit around) lies above the surface of both of the objects. This is not the case in the Earth-Moon system, where the barycentre lies roughly 1,700 km beneath the surface of Earth. In the case of Pluto-Charon, the barycentre is clearly above the surface of Pluto, so both Pluto and Charon orbit ar

Re:What the pluton?

[KiloByte (825081)]

The whole difference between a "planet" and a "moon" is a fallacy. It assumes things can orbit only a physical object, and not an immaterial object like a center of mass. The "official" definition fails not only in the obvious Pluton-Charon case, but even for Sun-Jupiter (putting the smaller bodies aside for now). We orbit not the Sun, but the center of mass of the Solar system, which is actually outside the Sun itself.

Thus, with the difference between "planets" and "moons" away, the classification that matters is:
* pieces of rock (Mercury, Venus, Earth, Moon, Mars, Phobos, Deimos, Europa, ...)
* sub-stellar balls of gas (Jupiter, Saturn, Neptune, Uranus)
* pieces of dirty ice

And to make it even harder, there is absolutely no reasonable boundary between "almost big enough to fuse" and "one particle". The difference between a "pebble" and a "boulder" isn't tangible.

Re:What the pluton?

[noahisaac (956470)]

The difference between a "pebble" and a "boulder" isn't tangible.

Having had both land on me at one point or another in my life, I beg to differ.

Re:What the pluton?

[by Anonymous Coward]

* sub-stellar balls of gas (Jupiter, Saturn, Neptune, Uranus)

I thought sub-stellar balls of gas came from Uranus.

Definitions

[j_w_d (114171)]

The difference between a "pebble" and a "boulder" isn't tangible.

"Pebble" has a formal scientific definition of small alluvial material from 4 to 64 mm diameter. "Boulders" are more than 256 mm diameter. Assuming the piece is a standard stony material such granite, drop a pebble of granite on your left toe and a boulder of granite on your right. I believe you will quite clearly note tangible, tactile differences. You might also try carrying a boulder in your back pocket and a pebble in a front pocket in your pants, or the other way around, if your are insecure with your girlfriend. Whenever you try sitting I again suspect you will note "tangible" differences.

Re:Solar Center of Mass

[Steve B (42864)]

Shouldn't the Sun have a hell of a tide due to Jupiter?

Tidal effects (the difference between gravitational acceleration at the near and far sides of an object) vary with the inverse cube of distance.

Re:What the pluton?

[jc42 (318812)]

The Earth and the Moon also revolve around a common point, which is inside the Earth.

A perspective I've read on this is that our moon's orbit is everywhere concave with respect to the sun. So it's more accurate to interpret the Earth-Luna pair as not really orbiting each other, but rather sharing a solar orbit. Two bodies that are close together in the same orbit do swap places periodically; there are several known cases of this in the Jupiter and Saturn systems. From a rotating frame of reference, they appear to be orbiting each other. But viewed in a static frame, they appear to be swapping the lead periodically. So the Earth-Luna pair could be more accurately considered a binary planet pair in a common orbit.

It's all rather nitpicky anyway. As numerous astronomers have pointed out here, they mostly don't use such vague terms as "planet". And an orbit isn't really a property of the bodies in an orbit; it's a property of the system.

The "debate" is basically a media event, based on people who take their grade-school science classes too seriously, and think that for some reason that the Solar System must contain exactly nine "planets".

Re:What the pluton?

[Andy Somnifac (971725)]

The "debate" is basically a media event, based on people who take their grade-school science classes too seriously, and think that for some reason that the Solar System must contain exactly nine "planets".

I think that one of the problems in this country (the US) is that we do not take grade school science seriously enough. We need those science classes to engage the kids and hopefully inspire some of them to a career in some scientific field.

Thats no moon...

[The Creator (4611)]

(Nor a space station)

It's not orbiting Pluto, but instead a point between itself and Pluto. If the mass of Pluto was higher, so that their common center of gravity was inside pluto, then Chauron whould indeed be a moon.

Re:Why?

[Adhemar (679794)]

I completely disagree with that the current system is better, but I don't see why your question merits the moderation (-1, Troll).

It's completely unsatisfactory to talk about "planets" when we don't know what is meant by a planet. Simply enumerating the ones in our solar system makes it very clear for our system, as we did so far, gives clarity for our solar system: the nine ones are planets, all others aren't. It doesn't state a reason. If asked why Pluto is a planet, and the very similar 2003 UB313 ("Xena") isn't, all we can say is: "historical reasons" or "convention".

When describing other solar systems, it is very normal to describe celestial bodies which are similar to the planets of our solar system, as "planets". But when is a body sufficiently like a planet of our own, to merit this description?

Really, it was high time we got a workable definition. Anything. Anything is better than an enumeration.

So, the International Astronomical Union (IAU) currently holds a highly-anticipated conference on the definition in Prague. It started last Monday, and a final decision is expected by next Thursday August 24, 2006.

The current proposal is:

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.

It has the added benefit that the minimum size (to exclude most Kuiper belt objects etc.) is not an arbitrary number, but a physical condition. The shape of objects with mass above 5 × 10^20 kg and diameter greater than 800 km would normally be determined by self-gravity. In borderline cases, we now must observe the roundness.

The pluton definition does have an arbitrary figure in its proposed definition: orbits around a star that takes longer than 200 years to complete.

Because

[Silver Sloth (770927)]

Science is always about testing the hypothesis against the data and redefining as required. You might as well say 'why don't we have four elements 'earth, water, air and fire', it's been that way for years.

If you're going to do science then you have to live with knowledge changing.