Pluto: Lost Satellite of Neptune or Planet on its Own?

[Kerrie]

I have always had a fascination of Pluto, is it labeled as a lost satellite of Neptune, or a planet on it's own because of Charon?

 

[(Q)]

Kerrie

The International Astronomical Union decided to continue to designate Pluto as a planet. The problem though, is that there is no complete definition of a planet as yet.

Rule #1, a planet must orbit the Sun. Rule #2, it must be large enough that it's own gravity is strong enough to maintain a spherical shape. If we were to go with these rules, there would exist about 12 planets in the Solar System. However, I don’t think Rule #2 is an accepted rule.

 

[rutwig]

Originally posted by (Q)
Rule #1, a planet must orbit the Sun. Rule #2, it must be large enough that it's own gravity is strong enough to maintain a spherical shape. If we were to go with these rules, there would exist about 12 planets in the Solar System. However, I don’t think Rule #2 is an accepted rule.

I suppose you mean Ceres and Pallas. Who is the 12th?

 

[(Q)]

Rutwig

Ceres and two other Kuiper Belt objects of which the names escape me.

 

[rutwig]

Originally posted by (Q)
Rutwig
Ceres and two other Kuiper Belt objects of which the names escape me.

Well, then I guessed correctly. These old guys which gave Bode so much headache!

 

[LURCH]

Wouldn't that be the object they just discovered? I believe in it is spelled "Quaor", or something close to that.

At any rate, if Pluto is disqualified as a planet, it will not be classified as an "escaped moon of Neptune", but rather a Kuiper Belt object that has been pulled into a "lock step" orbit with Neptune. Neptune's moon, Triton is also considered to have been a Kuiper Belt object at one time. The difference being, of course, that it actually was pulled into an orbit around the planet.

 

[RuroumiKenshin]

Why can't Charon be the planet, and pluto the moon?

 

[Kerrie]

is there any evidence that pluto/charon was once a satellite system of neptune?

 

[LURCH]

Originally posted by Zefram
Simply because Pluto is larger, though some refer to that system as a double planet (I may be incorrect but I don't think the center of mass of that system even lies within Pluto).

That is correct; Pluto and Cheron orbit a common center of gravity, and that center of gravity orbits the sun.

Interestingly, the earth-moon system is also considered by some to be a "double planet". Each of these systems is believed to be the result of two planets attempting to form in the same orbit, and colliding with one another. The biggest difference between the two systems is that while the moon is just over 1/4 the size of the earth, Cheron is just over one-half the size of Pluto.

 

[Kerrie]

i wonder if this is how charon looks from pluto...it would seem to me that if charon is nearly as big as pluto, it would be a spectacular site in the sky (that is if you were standing on pluto)http://starryskies.com/Artshtml/dln/7-99/pluto.jpg

 

[Sting]

I don't see any image Kerrie.

i wonder if this is how charon looks from pluto...it would seem to me that if charon is nearly as big as pluto, it would be a spectacular site in the sky (that is if you were standing on pluto)

That would be amazing. Slightly off topic but have you ever seen those movies or cartoons where the moon is practically covering the night sky? Is that positioning ever possible?

 

[ObsessiveMathsFreak]

I saw a programme that staed that the moon used to be much closer to the Earth and took up about a quater of the sky.

I think the definition of a planet should be based on its mass,. and not on it's relative size, shape or radius.

Think of a pluto sized object orbiting a dwarf star smaller that it was! I think it shouldd still be classed as a planet.

Or think of a dwarf star orbiting a very large star.

Mass would also help define planets in terms of their "livability" due to their gravity.

 

[Sting]

I saw a programme that staed that the moon used to be much closer to the Earth and took up about a quater of the sky.

Wow. Hah! I knew I wasn't going crazy.

I think the definition of a planet should be based on its mass,. and not on it's relative size, shape or radius.

You could compromise and use density

 

[Phobos]

Originally posted by LURCH
I believe in it is spelled "Quaor", or something close to that.

Close...Quaoar (pronounced Kwah-O-Ar)
Also called "2002 LM60". (discovered in 2002)
It's a spherical Kuiper Belt Object that is about half the size of Pluto (800 mile diameter vs. 1,400 miles).

At any rate, if Pluto is disqualified as a planet, it will not be classified as an "escaped moon of Neptune", but rather a Kuiper Belt object that has been pulled into a "lock step" orbit with Neptune.

Agree.

 

[J-Man]

Kerrie asked:
is there any evidence that pluto/charon was once a satellite system of neptune?

I believe the answer is: No.

Kerrie asked:
I have always had a fascination of Pluto, is it labeled as a lost satellite of Neptune, or a planet on it's own because of Charon?

As (Q) said, the IAU designation is planet; the debate was put to rest decades ago, though it often crops up on boards like this. However Pluto has "dual citizionship" with it's second classification as a KBO. It is mainly called a planet because of it's size, orbit and the fact that it was originally called a planet.

 

[Phobos]

Originally posted by J-Man
As (Q) said, the IAU designation is planet; the debate was put to rest decades ago, though it often crops up on boards like this.

Off the top of my head, I recall a recent debate by professional astronomers (led by Brian Marsden?) a couple of years ago where there was an official challange to the IAU designation. I'd have to check into the details, but y'all are correct that the IAU, which has the final say, still calls it a planet. And yep, pro-astronomers recognize that it's both a planet and a KBO.