Pluto-Charon. Dwarf planet and moon or double dwarf planet?

Page 1 of 1 [ 8 posts ] 

Signs654
Snowy Owl
Snowy Owl

User avatar

Joined: 4 Oct 2008
Age: 31
Gender: Male
Posts: 150

04 Jun 2009, 5:08 pm

Is Pluto-Charon a dwarf planet and a moon or a double dwarf planet?



Last edited by Signs654 on 04 Jun 2009, 5:48 pm, edited 1 time in total.

pakled
Veteran
Veteran

User avatar

Joined: 12 Nov 2007
Age: 64
Gender: Male
Posts: 7,015

04 Jun 2009, 5:15 pm

according to what I last heard, Pluto was a dwarf planet. Sharon would be a moon (or a dwarf moon? things that make ya go hmmm...;)

Great moons have lesser moons, in orbit just to spite 'em
and lesser moons have lesser moons, and so on ad infinitem...;)



twoshots
Veteran
Veteran

User avatar

Joined: 26 Nov 2007
Age: 36
Gender: Male
Posts: 3,731
Location: Boötes void

04 Jun 2009, 5:16 pm

Pluto's a dog.


_________________
* here for the nachos.


showman616
Snowy Owl
Snowy Owl

User avatar

Joined: 8 Feb 2009
Age: 67
Gender: Male
Posts: 170
Location: Washington DC, USA

21 Sep 2009, 5:42 pm

Interesting question.

Before we had satellite probes to check out the faraway planets we thought pluto was just one body- about the size of Mars.

We knew the solar system had five planets with moons.

Modest planets were known to have modest sized moons, big planets had big moons.

Mars ( modest sized) had two moons- but they are both little more than overgrown boulders, or uprooted moutains- jagged bodies no bigger than manhatten.

The Gas Giants ( like Jupiter, Saturn, and Uranus) were known to have variety of moons- some small irregular and boulder like. But they also had large spherical moons.

But there was one small rocky planet that did have a large jovian style spherical moon as a companion. This strangley endowed planet was: our own earth.

Earth was the only modest sized planet that had a satelite that was all of one fourth of its own diameter- the Moon. How bizarre!

The Earth-moon system is more like a "binary planet system". The only one that was known. Indeed our Moon is two thirds as wide as Mercurey- some might call it a respectable planet in its own right if it could be wrenched from eartth.

But we now know that pluto is also a "binary planet system".
The main planet- Pluto- is slightly larger than our moon. The subordinate body-Charon- is slightly smaller than our Moon. Both are smaller than Mercury ( and smaller than other known moons like Titan, Trition, and Gandymede-as well).

Pluto and Charon revolve around a common point- rather than Charon revolving arond Pluto because of their similarty in mass.

Actually the Moon doesnt actually revolve around Earth either. Both earth and the Moon orbit around a common point a few thousand miles above Earth.

Even though our moon is only little more than one percent the mass of the Earth- its bigger in relation to the Earth than any other moon in the solar system is to its master planet-except for Pluto's satellite- Charon.

The point is that Pluto turned out to be the one planet-moon system to be even more bizarre ( and more co-equal) than our own quite bizarre Earth-Moon system!



Last edited by showman616 on 21 Sep 2009, 5:57 pm, edited 1 time in total.

DeaconBlues
Veteran
Veteran

User avatar

Joined: 21 Apr 2007
Age: 58
Gender: Male
Posts: 3,661
Location: Earth, mostly

21 Sep 2009, 9:49 pm

Got your signs a bit reversed there, showman - the equilibrium point for the Earth-Luna system is several miles below Earth's crust. (Otherwise, the rotation of Earth around the point would be quite noticeable...)

I'd have to vote for calling Pluto-Charon a paired dwarf planet. The sizes are too close to say for sure that Charon's a moon, and besides, their equilibrium point is in free space between them.

Oddly enough, the minor planet Ceres (once thought of as the asteroid Ceres) has four moons, small bodies extracted from the rest of the Belt and in seemingly-stable orbits...


_________________
Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.


pakled
Veteran
Veteran

User avatar

Joined: 12 Nov 2007
Age: 64
Gender: Male
Posts: 7,015

22 Sep 2009, 1:04 pm

I think it's referred to as the Lagrange point (named after a small brothel in Texas...;)



DeaconBlues
Veteran
Veteran

User avatar

Joined: 21 Apr 2007
Age: 58
Gender: Male
Posts: 3,661
Location: Earth, mostly

22 Sep 2009, 4:16 pm

More seriously, for those whose hobbies don't include astrophysics or orbital mechanics, the LaGrange points are five solutions to a specialized three-body-problem setup (the problem being setting up three bodies in a stable orbital system). Joseph Louis LaGrange calculated that in a situation involving one comparatively-massive central body, and one slightly smaller orbital body, there are five points at which a body of relatively trivial mass can be located and have its orbit "held" (more or less) by the gravity of the other two bodies. In the case of the Earth-Moon system, those points are between Earth and Moon (L1), on the far side of the Moon but in a direct line with Earth (L2), directly opposite Earth from Moon (L3), or sharing an orbit with the Moon but sixty degrees ahead of or behind it in orbit (L4 and L5). Of those points, the ones with the greatest librational stability (the ones in which gravity tends to keep the body in its orbit, rather than letting it fall out) are L4 and L5, which is why it has been proposed to place O'Neill colonies in those points. (The stability can be observationally confirmed with the Sun-Jupiter system; its L4 and L5 points are occupied by the Trojan asteroids, leading to these points sometimes being referred to as "Trojan points".)


_________________
Sodium is a metal that reacts explosively when exposed to water. Chlorine is a gas that'll kill you dead in moments. Together they make my fries taste good.


showman616
Snowy Owl
Snowy Owl

User avatar

Joined: 8 Feb 2009
Age: 67
Gender: Male
Posts: 170
Location: Washington DC, USA

22 Sep 2009, 7:58 pm

I stand corrected.

The book must've said "3000 miles from the center of the earth", rather than 3000 from the surface of the earth- which would mean the fulcrum of the earth-moon system would indeed be about a thousand miles below the surface of the Earth.

But still- we forget how odd it is that such a small planet as Earth has such a big moon.
Our set up could be called a binary planet system. And pluto- a binary dwarf planet system.