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

In summary, there has been a long-standing debate on whether Pluto should be classified as a planet or a lost satellite of Neptune. The International Astronomical Union has designated Pluto as a planet, but there is still no complete definition of a planet. Some believe that Pluto should be disqualified as a planet and classified as a Kuiper Belt object instead. There is no evidence to suggest that Pluto and Charon were once a satellite system of Neptune. Pluto's dual citizenship as both a planet and a Kuiper Belt object is mainly due to its size, orbit, and original classification as a planet.
  • #1
Kerrie
Staff Emeritus
Gold Member
844
15
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?
 
Last edited by a moderator:
Astronomy news on Phys.org
  • #2
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.
 
  • #3
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?
 
  • #4
Rutwig

Ceres and two other Kuiper Belt objects of which the names escape me.
 
  • #5
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!
 
  • #6
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.
 
Last edited:
  • #7
Why can't Charon be the planet, and pluto the moon?
 
  • #8
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).
 
  • #9
is there any evidence that pluto/charon was once a satellite system of neptune?
 
  • #10
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.
 
  • #11
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
 
Last edited by a moderator:
  • Like
Likes Abullais Ghazi
  • #12
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?
 
  • #13
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.
 
  • #14
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
 
  • #15
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.
 
  • #16
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.
 
  • #17
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.
 

1. What is the current classification of Pluto?

Pluto is currently classified as a dwarf planet by the International Astronomical Union (IAU), meaning it does not meet the criteria to be considered a full planet.

2. Why was Pluto downgraded from a planet to a dwarf planet?

In 2006, the IAU established new criteria for what qualifies as a planet. Based on these criteria, Pluto was reclassified as a dwarf planet because it did not meet the third criterion, which states that a planet must have "cleared the neighborhood around its orbit."

3. Was Pluto ever considered a planet?

Yes, Pluto was considered the ninth planet in our solar system for over 75 years, from its discovery in 1930 until its reclassification in 2006.

4. Why is there debate over Pluto's classification?

Some scientists and members of the public argue that Pluto should still be considered a planet, as it has unique characteristics and holds historical significance. Others believe that the IAU's criteria for planets should be followed strictly and that Pluto does not meet all the requirements.

5. Is there evidence that Pluto was once a satellite of Neptune?

No, there is no evidence to suggest that Pluto was ever a satellite of Neptune. While some theories propose that Pluto may have formed in a similar way to Neptune's other moons, there is no concrete evidence to support this claim.

Similar threads

Replies
3
Views
301
Replies
17
Views
2K
  • Astronomy and Astrophysics
Replies
2
Views
985
Replies
16
Views
2K
Replies
5
Views
3K
  • Astronomy and Astrophysics
Replies
8
Views
1K
  • Astronomy and Astrophysics
Replies
27
Views
5K
  • Astronomy and Astrophysics
Replies
15
Views
1K
  • Astronomy and Astrophysics
Replies
2
Views
1K
  • Astronomy and Astrophysics
Replies
1
Views
1K
Back
Top