IAU Redefines the Solar System: 12 Planets, Countless Possibilities

[BobG]

The International Astronomical Union is about to decide the Solar System has 12 planets. The new planets:

Xena would become the most distant planet.

Charon would become a planet. Since Pluto and Charon both orbit a point in space outside of both, Pluto and Charon become a double planet system.

Ceres, the first and largest asteroid discovered, becomes the solar system's smallest planet. Actually, when Ceres was first discovered, it was classified as a planet and was later downgraded to asteroid status.

http://news.yahoo.com/s/space/20060816/sc_space/nineplanetsbecome12withcontroversialnewdefinition

Don't expect the number to remain at 12 very long. The number of planets in the solar system will jump to anywhere from 24 to 53 fairly quickly, with the number eventually rising into the hundreds or thousands.

The new definition is pretty simple: "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." (Charon isn't a satellite of Pluto since the two orbit a point in space outside of both objects).

 

[Danger]

I had enough trouble trying to remember the ones that we already have. :grumpy:
It would have been a lot easier if they'd just downgraded Pluto.

 

[Astronuc]

Well that makes an even dozen. So that should be easier right?

Draft resolution on the matter.
http://www.space.com/scienceastronomy/060816_planet_resolution.html

 

[Gokul43201]

Ceres, the first and largest asteroid discovered, becomes the solar system's smallest planet.

Does it then lose the "1" prefix?

I'm not sure whether Ceres will feel like she's being upgraded or downgraded.

 

[Rach3]

http://www.space.com/scienceastronomy/060816_planet_resolution.html

(3) We recognize Pluto to be a planet by the above scientific definition, as are one or more recently discovered large Trans-Neptunian Objects. In contrast to the classical planets, these objects typically have highly inclined orbits with large eccentricities and orbital periods in excess of 200 years. We designate this category of planetary objects, of which Pluto is the prototype, as a new class that we call "plutons".

"plutons". :rofl:

 

[Rach3]

Xena would become the most distant planet.

Not Xena yet, right now it's 2003 UB313.

 

[JasonRox]

Sounds like Astronomers are desparate for attention.

 

[Chi Meson]

Sounds like Astronomers are desparate for attention.

A good point. Seems to be a long season between comets.

 

[Astronuc]

I seem to remember a term "planetoids", which was probably 35+ years ago. I was wondering what happened to the usage.

I found this on Wikipedia - http://en.wikipedia.org/wiki/Minor_planet

Of course, the singificance of recent events means that Ceres and some other objects may have their designations changed.

 

[scott1]

There's already a thread about this:
https://www.physicsforums.com/showthread.php?t=129085

 

[scott1]

Not Xena yet, right now it's 2003 UB313.

I kind of like calling just 2003 UB ₃₁₃. Kind sounds cool and it's differn't then naming after a roman god.

 

[SpaceTiger]

I don't really care how they classify them, I'm just happy to see them finally putting together a self-consistent scheme. It should have been done long ago, IMO.

 

[DaveC426913]

Cuz you got to hate those roman goods.

 

[DaveC426913]

Oh MAN this is going to mess up all those Astrologers...

 

[Quaoar]

Oh MAN this is going to mess up all those Astrologers...

They seemed to adapt quite nicely to Pluto's addition...and that was less than 80 years ago...

 

[Line]

Xena, is that the Keiper object that's out in The Ort Cloud? I don't think Ceres should be a planet. Is it round?

 

[Gokul43201]

I don't think Ceres should be a planet. Is it round?

Very well rounded - an excellent candidate!

 

[Phobos]

"plutons"...now is that pronounced "plu-tons" (as it looks) or "plu-tones" (to better match "Pluto")?

"Downgrading" Pluto may be easier (I'll never memorize the eventual dozens/hundreds/whatever of planets), but adding planets may be more exciting/positive for the general public ("this just in...new planet discovered!") and may better promote science education. Heck, even astronomers may find it more fun even if they know its just semantics. But like SpaceTiger said, it's good to have some tighter definitions (even considering http://www.badastronomy.com/bablog/2006/08/15/congratulations-its-a-planet/")

 

[Quaoar]

"plutons"...now is that pronounced "plu-tons" (as it looks) or "plu-tones" (to better match "Pluto")?

"Downgrading" Pluto may be easier (I'll never memorize the eventual dozens/hundreds/whatever of planets), but adding planets may be more exciting/positive for the general public ("this just in...new planet discovered!") and may better promote science education. Heck, even astronomers may find it more fun even if they know its just semantics. But like SpaceTiger said, it's good to have some tighter definitions (even considering http://www.badastronomy.com/bablog/2006/08/15/congratulations-its-a-planet/")

I've done the math for when the Earth-moon barycenter will be outside of the planet, and I get substantially different results...

Distance to barycenter: M_Moon / (M_Earth + M_moon) * new_distance

Set this equal to the Earth's radius, we have:
.0122 * new_distance = 6378km =>
new_distance = 524000km

distance_traveled = new_distance - current_distance = 524000km - 385000km = 139000km.

Time to travel distance = (139000km) / (4 cm/yr) = 3.48 BILLION years.

This guy simply divided the distance of the barycenter from the surface by the rate of travel, which is NOT correct.

 

[Phobos]

I've done the math for when the Earth-moon barycenter will be outside of the planet, and I get substantially different results...

Good catch, Guillochon. He corrected himself too in a later post...
http://www.badastronomy.com/bablog/2006/08/18/i-made-a-massive-mistake/

 

[Astronuc]

To be or not to be . . . a planet? That is the question.

Pluto's Planetary Status Teeters -- Again
http://www.npr.org/templates/story/story.php?storyId=5691890

All Things Considered, August 22, 2006 · In a stunning reversal of fortune, it now seems likely that Pluto will lose its title of planet. Astronomers have been debating for years whether Pluto should count as a planet.

On the one hand, the say, it always has. On the other hand, it's much smaller than Earth, smaller even than Earth's moon.

Scientists meeting in Prague with the International Astronomical Union were presented with a new definition of the word "planet" last week. That definition would have included Pluto as a planet. But the proposal met with fierce protests. Opponents argued that there are hundreds of objects like Pluto out beyond Neptune.

Critics say they will back a definition that would consider designating a sort of dwarf object -- but not a planet.

 

[Quaoar]

From what I've been reading, I wouldn't be surprised that we come out of this meeting with no planet definition at all:

"The vote is a "yes" or "no" proposition, so it is possible that the meeting will end with no planet definition." [http://www.space.com/scienceastronomy/060823_planet_vote.html" ]

It's a shame, too...I liked the proposal first proposal quite a bit (the one that would have added Charon/Ceres/Xena).

 

[Gelsamel Epsilon]

I say we downgrade pluto, this adding of Xena Ceres and Charon are rediculous, and aparently there are 20+ other candidates. So we're going to have 30 planets now? I especially think Charon and Ceres were mistakes in adding because uptil now Charon was classified as a moon but because of it's unusual orbit around pluto it is now a planet. And Ceres is a freakin' asteroid.

 

[Quaoar]

I say we downgrade pluto, this adding of Xena Ceres and Charon are rediculous, and aparently there are 20+ other candidates. So we're going to have 30 planets now? I especially think Charon and Ceres were mistakes in adding because uptil now Charon was classified as a moon but because of it's unusual orbit around pluto it is now a planet. And Ceres is a freakin' asteroid.

I never understood the aversion to more than ~10 planets in the solar system. So what?

Ceres might be a little TOO small...I think they should wait until they can get a better look and truly determine if its in hydrostatic equilibrium. If it is, I have no problem with it becoming a planet.

The barycenter definition seems to be the only concrete way to distinguish a double planet from a planet-moon system. I think all the other methods are very arbitrary.

I think the problem is that people have it in their heads that all planets must be larger than all moons, and I really don't believe that this should be the case.

 

[RandallB]

I never understood the aversion to more than ~10 planets in the solar system. So what?

I think the problem is that people have it in their heads that all planets must be larger than all moons, and I really don't believe that this should be the case.

I think they would just like to see it based on some meaningful definition of what a planet is – not just how many can we add to the count.
Maybe two general categories;
1)Large rocky inner planets found in near circular orbits around their sun and
2)Much Larger Gas giants also in near circular orbits but usually expected much outside the area of the rocky planets.
Now a solar system should be expected to have rocky asteroids and dirty snowball chunk of ice comets, but should we call large ones of those planets just to satisfy adding a few more names to be honored as discoverers.

Frankly if an American had found one of the first 8 instead of the ninth, I suspect Pluto would have been down graded some time ago.
It shouldn’t stay on (or come off) the list because of politics.
And if it does come off – it is just as easy to say “SO WHAT” if the categorization makes better sense why not.

 

[LURCH]

I'm glad they decided to downgrade Pluto, and leave out Cheron. They and the other Kuiper Belt Objects are quite obviously not the same thing as the classical planets (which is goes to the very heart of the reason for having a word like "planet").

These objects and Cerus and Xena are something very much "other" than objects like Earth or Jupiter or even Mercury, and should not be reffered to as if they were the same thing, just for the sake of accuracy.

 

[Quaoar]

Don't expect this resolution to remain in effect for long, there's already a petition going around to overturn the IAU's decision.

 

[big man]

I thought that Pluto had an atmosphere?
This would distinguish it from the other objects...but then I don't know if the other objects like Ceres have atmospheres themselves.

Sorry if that is a bit of a stupid thought, but I don't know much about this obviously.

 

[Astronuc]

I don't think Mercury has much of an atmosphere.

Solar System Shrinks with Pluto's Demotion
http://www.npr.org/templates/story/story.php?storyId=5703014

Morning Edition, August 24, 2006 · Leading astronomers declare that Pluto is no longer a planet, shrinking the solar system from nine planets to eight.

Pluto was discovered in 1930. It lost its planetary status when the International Astronomical Union approved a definition for planets that Pluto fails to meet.

Pluto will now belong to a new category of "dwarf planets," similar to what long have been termed "minor planets."

Earlier this year NASA launched the New Horizons spacecraft on a 9 1/2 year journey to Pluto. The probe will allow scientists to better understand the distant body.

Interesting week - http://en.wikipedia.org/wiki/2006_redefinition_of_planet


Astrologers Join Debate of Pluto's Planetary Status :rofl: :rofl: :rofl:
http://www.npr.org/templates/story/story.php?storyId=5697880

Bad luck now when Pluto is in . . . :rofl:

 

[Gelsamel Epsilon]

I'm somewhat happy that they downgraded pluto from a planet, but I'm disappointed at how they did it, having to "clear the neighborhood around it's orbit" is the biggest cop-out limitation they put in there just to keep pluto out especially because it isn't the fact that there are heaps of rocks in it's "neighborhood" but because it crosses neptunes orbit! I can't believe how much of a cop-out that is.

What if a planet as large as Jupiter followed plutos orbit but in a way so that neptune was always very far away and they never affected each other in a way to "Clear the neighborhood" they would be called "Dwarf planets" despite their size.

 

[Reshma]

"My Very Educated Mother Just Showed Us Nine Planets", the famous mnemonic to remember the names of the nine planets when we were kids viz. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
I wonder what kind new mnemonic has to be invented with the recent developments in the order of planets .

 

[LURCH]

Yeah, that is kind of a cop-out, isn't it? I mean, by that definition, Neptune should also be downgraded, because it hasn't cleared Pluto out of its orbit.

 

[Quaoar]

It seems to me they picked a definition where they can call anything a planet or a non-planet, depending on how they "feel" about the object. Really, this whole process was a complete waste of time, and the definition they came up with is downright pathetic.

 

[LURCH]

Come to think of it, since there are still thousands of NEO's, we don't live on a planet, do we?

 

[Line]

How could there be 12 when they just announced Pluto isn't a planet?