Vote on the IAU draft resolution "Definition of a Planet"

[TheBigDog]

I want to put out an alternate theory that Pluto is a moon of Neptune.

 

Bill

[cwes99_03]

Ok, but what basis do you have for your theory, and is it just a theory or is it a Theory. Definitions of

 

Better define moon while you are at it.

[TheBigDog]

Ok, but what basis do you have for your theory, and is it just a theory or is it a Theory. Definitions of

 

Better define moon while you are at it.

It is a bit shaky, but worth discussing. On one of these threads the topic of Pluto crossing Neptune's orbit came up. I figured that if we waited long enough Neptune would eventually change the orbit of Pluto thus clearing its path of the interloper. But when I researched it I found that they have a precise 3:2 orbit time. This means that they will never get close enough to actually encounter each other in a way that would change their orbits. But it also explained that this happens because of Neptune's influence on Pluto at their closest points. So in effect, the orbit of Pluto is controlled by the orbit of Netune. And while Pluto does not orbit around Neptune per say, its orbit around the sun is controlled by Neptune, with the bigger planet forcing the smaller one to stay in phase with its orbit.

 

http://seds.lpl.arizona.edu/nineplanets/nineplanets/plutodyn.html

 

Bill

[Qfwfq]

Pluto and Neptune don't orbit their centre of mass. They were both discovered because of their gravitational influence on previously known planets, so this isn't a novelty.

[cwes99_03]

So in effect, the orbit of Pluto is controlled by the orbit of Netune. And while Pluto does not orbit around Neptune per say, its orbit around the sun is controlled by Neptune, with the bigger planet forcing the smaller one to stay in phase with its orbit.

 

http://seds.lpl.arizona.edu/nineplanets/nineplanets/plutodyn.html

 

Bill

 

This is interesting, and I guess I kind of already knew some of that, though I didn't know that because of the out of plane orbit that the orbits don't actually cross over each other but above and below each other.

 

http://seds.lpl.arizona.edu/nineplanets/nineplanets/gif/dobro3.gif

 

That was a cool graph, because it takes the planet positions with respect to the orbit of neptune. I'll have to study that a bit more because of the really odd shape of Pluto's path compared to Neptune's. What I'm wondering is if that particular graph shows mean distance (due to both z and r) or just a projection (looking at the orbits from above) of the systems orbital radius. One thing it does show is that the closest Pluto gets to Neptune is 17 AU which is no where near close enough to be affected.

 

BTW, each of the curls shows the apparent retrograde motion of Pluto compared to Neptune's view of the sky. That is an awesome graph.

 

Maybe the author should do the same with Charon's orbit.

 

 

What I don't get about the resolution is what particularly is meant by hasn't cleared the path. Because to me a moon is in synchronous orbit with a planet, so how does that work? The page above shows that Neptune and Pluto don't get even close, so obviously you couldn't say that they are in the same orbital region. Earth, Mercury, Venus, and Mars are all closer to each other than Pluto and Neptune.

[CraigD]

[Pluto and Neptune] were both discovered because of their gravitational influence on previously known planets …

While it’s true that Neptune was predicated by its gravitational influence on previously known planets (mainly Uranus), the same’s not true of Pluto.

 

Although a 9th planet was predicted ca. 1910 by several astronomers, they predicted another large planet. Pluto/Charon is not massive enough to have a detectable effect on the orbit of Uranus – the prediction of a 9th planet was actually due to an error in estimating Neptune’s mass.

 

That Pluto was discovered near the position predicted for a large 9th planet appears to be in part a coincidence, and in part due to so many people spending so much time searching that vicinity for the incorrectly predicted large planet.

 

21st century finds of Pluto-like object such as “Zena” lead me to suspect that finding many more such bodies is nearly certain given sufficient observation. Given uncertainty in estimates of the mass of the Kuiper belt, and the lack of a detailed, compelling model of how Kuiper objects form, I see no reason not to expect that we may not someday discover much larger bodies much further out than Pluto, perhaps some as big as some of the inner planets.

 

The Kuiper belt excites the imagination!

[Qfwfq]

Pluto/Charon is not massive enough to have a detectable effect on the orbit of Uranus

:) Actually it was Neptune I meant, it was just what I could remember from my childhood books, back in the '70s. :eek2: