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The 12 Planets

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Pluto remains a planet, a double planet at that with its moon, Charon getting bumped up to planet status. Two other planets, Ceres (between Mars and Jupiter) and Xena (beyond Pluto/Charon) get added. What do you think about these new planet, how will you remember their names?

Nine no longer: Panel declares 12 planets [The Boston Globe]

Cosmic Debate: What's Up With the Planets? [NASA.gov]

The IAU draft definition of "planet" and "plutons" [IAU]

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According to the Hartford Courant, the 2 criterion for being a planet are: must orbit a star but not be a star; and be big enough to be round (over 500 miles in diameter). The first is odd, I'm no expert, but where do stars orbit other stars? Second, why make the cutoff 500 miles in diameter? Why not up it to 1000 miles? I think an object less than 500m/dia isn't generally round, but I don't see the need for it to be the minimum size that allows for a round object. This would exclude Charon and Ceres which are very small, and it would also exclude the 200 some such other objects in the SOlar Sytem that are under review and could eventually be included.

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It is a rather interesting development and will take a litte getting used to. I guess consistancy means that Ceres needs to be re-classified. It has been speculated for decades there was a 10th planet but this is the first time I have heard they gave a name to it, Xena. At one point I had heard that it would be named Persephone if it were to be discovered.

There are not any good photos of Pluto. The best photos from the hubble telescope appear as nothing but a bright blob. Hopefully the New Horizons probe will arrive there in working order in 2015 and we get a much better look at what is going on.

Some trivality on Pluto. From January 1979 thru February 11 1999 Pluto was the 8th planet as it's very eliptical orbit moved it inside that of Neptune. That won't happen again until the year 2227.

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So is this truly a done deal that there are now 12 planets that will be going into the science textbooks or is it still under debate? I've been following it a little on NPR podcasts and what has shown up on the web but I haven't heard that it was a definitive answer yet.

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According to the Hartford Courant, the 2 criterion for being a planet are: must orbit a star but not be a star; and be big enough to be round (over 500 miles in diameter).

What about the system Oph 1622, in Ophiuchus ? Two exoplanets... without star !

They are 'planemo' twins (PLANEtary Mass Object).

http://en.wikipedia.org/wiki/planemo

("Xena" is 2003 UB313)

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What do you think about these new planet, how will you remember their names?

We had a mnemonic, but we hadn't anticipated Ceres and Charon. Look at the first letters :

Me Voici Toute Mignonne, Je Suis Une Nouvelle Plan

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Ceres is a planet once again!

We of the Coalition for the Signification of Ceres are dutibly pleased!

From hence forth there shall be much rejoicing!

(also known as, drinking a few beers, and looking out the telescope)

Actually shouldn't Sedna also be included then? wouldn't that make the count 13?

Some other potential planets:

Varuna

Quaoar

2003_EL61

Orcus

2005_FY9

we could have up to 18 planets, and counting upward by the time the Kuiper belt is fully understood.

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Ceres is a planet once again!

We of the Coalition for the Signification of Ceres are dutibly pleased!

From hence forth there shall be much rejoicing!

(also known as, drinking a few beers, and looking out the telescope)

Actually shouldn't Sedna also be included then? wouldn't that make the count 13?

Some other potential planets:

Varuna

Quaoar

2003_EL61

Orcus

2005_FY9

we could have up to 18 planets, and counting upward by the time the Kuiper belt is fully understood.

Um, 2003 EL61 look like an egg.

I expect 2005 FY9, Sedna, Orcus, Quaoar, Varuna.

Other candidates (planetoids) : 2002 TX300, 2002 AW197, Ixion (28 978 Ixion) in the kuiper belt and the asteroids : Vesta, Pallas, Hygiea.

http://www.solarviews.com/eng/asteroid.htm

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According to the Hartford Courant, the 2 criterion for being a planet are: must orbit a star but not be a star; and be big enough to be round (over 500 miles in diameter). The first is odd, I'm no expert, but where do stars orbit other stars? Second, why make the cutoff 500 miles in diameter? Why not up it to 1000 miles? I think an object less than 500m/dia isn't generally round, but I don't see the need for it to be the minimum size that allows for a round object. This would exclude Charon and Ceres which are very small, and it would also exclude the 200 some such other objects in the SOlar Sytem that are under review and could eventually be included.

I think they should've added that the object doesn't orbit another object/planet. I mean, I thought the hierarchy was always sun --> planet --> moon. I don't think moons should be planets because they orbit another object besides the star. But that's just me.

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It has been speculated for decades there was a 10th planet but this is the first time I have heard they gave a name to it, Xena.

Xena has not been officially named yet, that's just what the discoverer is calling it. Supposedly it has a satellite that they are calling Gabrielle.

So is this truly a done deal that there are now 12 planets that will be going into the science textbooks or is it still under debate?

The full comission has to vote to approve the comittees recommendation, but it has strong support and is likely to pass. They vote at the end of the month I believe.

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Xena has not been officially named yet, that's just what the discoverer is calling it. Supposedly it has a satellite that they are calling Gabrielle.

Sigh... that's ridiculous. Funny, but ridiculous....

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It's not official yet!

There are stars that orbit other stars.

But I thought also a planet can't orbit another planet, but with Pluto and Charon, some people are already calling them a binary planet. But I think Charon is a moon, Ceres is a daggone asteroid.... I'd accept "Xena" and "Sedna" and some others out there past Pluto.

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It's not official yet!

There are stars that orbit other stars.

But I thought also a planet can't orbit another planet, but with Pluto and Charon, some people are already calling them a binary planet. But I think Charon is a moon, Ceres is a daggone asteroid.... I'd accept "Xena" and "Sedna" and some others out there past Pluto.

Pluto and Charon are "mutual moons". :P The centre of gravity is between them not in Pluto.

Yes the decision should come in a week's time.

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^^^ absolutely correct---Pluto and it's satellites revolve around a center of gravity between Pluto/Charon.

Pluto has three known moons! What an awesome planet, and I do say planet:)

Sedna is surely a planet as well, and Xena too.

I have been enjoying the theories about "Dark Star".....that a burned out dwarf star is part of a binary system with our sun. Supposedly it is soooooooooooooo far away, and so dim it has "eluded discovery".

Most stars in the Universe are part of a binary star system. Why should ours be different?

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I have been enjoying the theories about "Dark Star".....that a burned out dwarf star is part of a binary system with our sun. Supposedly it is soooooooooooooo far away, and so dim it has "eluded discovery".

But the effects of its gravity would be immediately observable on the orbits of the other objects out there. This is how they found Xena. They looked at anomolies in Pluto's orbit and found the only way to explain it was there was another undiscovered planetary mass out there affecting it. It took many decades to actually discover Xena

There could not be something with the massive gravity well of a drawf star in the solar system without it being known. None of the orbits of the outer planets would match up with the calculations that assume it is not there.

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Some theorists believe our solar system's outer comet belt does wierd orbits because possibly they orbit both our sun, and Dark Star.

Dark Star wouldn't have an enormous gravity....it would be expected to be a rather small burned out shell.

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Dark Star wouldn't have an enormous gravity....it would be expected to be a rather small burned out shell.

Any mass that was large enough to actually begin nuclear fusion and briefly burn as a star would have a huge gravity well. If Xena was large enough to be detected by its gravitational effects on Pluto then a dark star would be immediately known. Something that massive would affect the orbits of all of the outer planet. These so called "theorists" would have to address this fact and if they haven't then they are making claims that simply are not true or based in science.

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Theories are just that:)

If we don't dream of all the possibilites when it comes to science, we cheat ourselves.

80 years or so ago no one knew Pluto existed. It takes time to learn the "facts" but in the meantime it's still fun to speculate about the wonders of possibilty:)

Dark Star is certainly an exotic concept.

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Theories are just that:)

Well no, they are usually supported by some scientific observation. The absence of any effects of gravity from this dark star would certainly eliminite the possibility of one being in our solar system.

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I really hope that Xena doesn't remain as Xena, I hope they actually call it Persephone as has been suggested....

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I'm surprised no one has asked this yet but by definition, wouldn't our moon also be conside3red a planet itself?

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Ahh, nevermind. I have my answer.

Moons are excluded from planetary status, using a criterion that depends on the relative mass of two bodies that are gravitationally tied. If one body is much smaller than the other, then it is considered a moon. Pluto and Charon are closer in mass, and so they are dubbed a double planet. The Earth's moon is round and much larger than Pluto, but it is so much smaller than Earth that it is considered a moon, not a planet

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Now if the Moon were to be kicked out of our orbit and start its own around the sun, it'd be a planet. But that might make our planet go into chaos and wipe us out.

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Ive also heard of the theory of a planet in or solar system that exist no more. I heard the astroid belt between Earth and Mars is whats left of the planet.

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