[TopAce]

What's the point in reducing he number of planets (or at least what WE consider planets) from 9 to 8, anyway? I don't see the point. It's smaller than any other planets, but still...

Can you give me any sensible explaination why Pluto is a planet but UB-313 isn't?....

I didn't know a thing about UB-313 apart from its name. So I cannot give you an explanation of any sort.

[MrBig101]

What's gonna happen to all the 9 planet sayings to remember them? 

[aldo_14]

What's the point in reducing he number of planets (or at least what WE consider planets) from 9 to 8, anyway? I don't see the point. It's smaller than any other planets, but still...

Can you give me any sensible explaination why Pluto is a planet but UB-313 isn't?....

I didn't know a thing about UB-313 apart from its name. So I cannot give you an explanation of any sort.

It's right next to UB-312

(oh, and it's also larger than Pluto; along with its moon it's the most distant known object in the solar system)

[Ulala]

Yay Plutonoids, something for the Klingons to fly around!!

That's no Plutonoid... it's a space station!

[Mongoose]

As I said somewhere else:

This decision actually makes good scientific sense. Pluto really never was nothing more than a very large example of a Kuiper belt object. Of course, at the time of its discovery, the Kuiper belt wasn't really known, so it was given the designation of "planet" instead. (Even that wasn't without controversy, though.) In terms of the model of solar system formation, which explains why the inner planets are small and rocky and the outer are large gas giants, Pluto never really fit in. At least this definition makes a hell of a lot more sense than the whole "12 planets now, possibly thousands in the future" idea that was tossed around at the conference a week or so ago.

And it's certainly not "goodbye" to Pluto; it's not like it's going anywhere. It's actually taken on an important new role, as the prototype of a whole new classification known as "dwarf planets." This decision certainly doesn't affect the status of the New Horizons mission, which should hopefully get us our first close-up pictures of Pluto and Charon around 2015 or so.

(All of that being said, the sentimental side of me does feel a little bit sad for it...)

[Nuke]

i have a feeling pluto will get re-promoted to a planet in its distant future when its orbit flatens out and gets normalized by the gravitational forces of the other planets. thats asasuming they dont change the scientific definition again.

[watsisname]

Pluto's been going around the sun for billions of years like that, so I really don't think we can expect that to happen anytime soon.  I'd bet the sun will swell up and fry the Earth before we can even consider worrying about Pluto's orbit changing.

As for Pluto's "demotion", I'm actually somewhat pleased.  I've always disliked calling it a planet, since it didin't follow the same genesis that the other planets did.  I am perfectly understanding for those who are irritated about it though.

[Nuke]

orbits arent exactly set in stone. aside from gravity pulling inward from the sun and other planets (which is countered by planets velocity), you also have the vertical tug which occurs when the "pluton" or whatever deviates from the ecliptic plane of the solar system. this tug pulls the pluton down when its above the plane and up when its below. this is why the 8 planets are all pretty much flat, it just seems to me that pluto is a tad late at achieving this. yes it may take housands if not millions of years, but its likely. to me pluto is either a protoplanet or a comet in an eccentrc (for a comet anyway) orbit. pluto can be a planet if its orbit changes to fit the new scientific definition.

[Bobboau]

the thing is that up down pull has no friction so it loses no energy, so it never stops,the reason why the other planets are so close is because they formed from a disk of that shape.

[Nuke]

what likely defined the plane is the 2 largest objects in the solar system, being the sun and jupiter. all the other objects most likely followed suit, as it would have taken less time for their orbits to change to jupiters, than vice versa. jupiter would have deviated slightly under the varing gravitational forces in the solar system, however its mass dampened that effect. therefore id assume that jupiters orbit is only slightly different from when the planet was formed. im curious if its known if the solar system's plane is the same as the rest of the galaxy.

[karajorma]

The way I've always understood the formation of the solar system the planets formed out of the already flat accretion disc not all over the place and then moving into settled orbits.

[watsisname]

Karajorma gets a cookie.  (In other words, he's right.)

[Nuke]

that is one theory, but that doesnt mean other theorys need to be cast aside. it could have very well been a diffuse ball of dibrits before forming objects and then flattened out later.

[Flipside]

The disc theory is the only one that properly explains planetary rotation atm iirc, if you consider that the Sun is orbitting the milky way, as well as spinning itself. As you say, it doesn't make the others suggestions impossible, but far les likely with regards to what we currently know.

[watsisname]

The current theory is that the solar nebula condensed out of a *roughly* spherical cloud, which then flattened out as it collapsed, which also increased its rotation (conservation of angular momentum).  The planets formed after the inner solar disk flattened out, while the outer regions formed into the Kuiper Belt and Oort Cloud.

So there's some truth to it forming from a spherical cloud, but a distinction needs to be made on the sequence of events in its formation and evolution.

[Nuke]

still its not too far off to say that the mass which eventually became jupiter helped to stabilize and flatten the accretion disc.

[Flipside]

Well, the theory goes that Jupiter only needs to gain something like 12% more mass to start nuclear reactions in the core (It's already very 'hot') which would have led to it being a binary partner to the Sun, with Europa etc being a seperate planetary system.I wouldn't be suirprised if a mass of that type had an effect on the formation of the system, chances are moderate to high, I would say, that at least one or two of Jupiters' moon were possibly inner planets at some point, between Mars and Jupiter and got caught in the Gravitational tide.

[watsisname]

If you're interested in Jupiter's moons, I suggest checking this out:
http://www.ifa.hawaii.edu/~sheppard/satellites/

The Galilean moons (Io through Callisto) formed in conjunction with Jupiter, which is why they all have nice, *almost* circular, low-inclination orbits.  But Jupiter's gravity captured a great deal of asteroids and other things, which end up in highly eccentric and inclined orbits, and many of them are retrograde (orbiting backwards relative to Jupiter's rotation).  Pretty fascinating stuff.

[BS403]

It's right next to UB-312

(oh, and it's also larger than Pluto; along with its moon it's the most distant known object in the solar system)

I thought the percent error made it possibly larger or smaller than pluto

[karajorma]

Depends on who you listen to.

The BBC put it at 2600km which would make it bigger than Pluto's 2360.

Wikipedia has Pluto at 2306±20 km and UB-313 at 2400 km ± 100 km which could make Pluto just about the bigger one of the two if the errors are in its favour.

Other sites have different sizes for both of them. Till anyone says for certain I think the general assumption is that it's bigger than Pluto.