Pluto and Charon

[Helio]

The velocity vector of the center of mass of an isolated system, as measured in an inertial coordinate frame, cannot change except from an external influence.

As the planets in a Solar System move around and change places the velocity vector of the barycenter of that sytem will not change as observed from an inertial reference frame.

If you are basing your coordinate frame on one of the revolving planets then it is not an inertail frame and the barycenter will be seen to wobble all around.

Thanks Bill. I think I’m getting it, now.

In the seesaw case it is not an isolated system. As the four little people move around they are pushing the seesaw legs against the Earth and moving the Earth slightly.

The see-saw analogy won’t work because it fails to make the big guy move, unlike our solar system’s Sun. As the planets align opposite the Sun, the Sun will have moved farther from the barycenter, which remains fixed, thus balancing the system. We can see this in the Pluto-Charon animation, not that it’s accurate.

 

[Catastrophe]

From #1:

Pluto's moon Charon sports a red polar cap that forms as seasons change | Space.com Forums

Any other interesting observations on Pluto's moons?

Cat

 

[Helio]

From #1:Any other interesting observations on Pluto's moons?

Try this.

 

[Catastrophe]

Try this.

DO NOT MISS THIS!

Cat

 

[Catastrophe]

The odd orbits of Pluto's five known moons may be the result of a gigantic impact that occurred about four billion years ago, a new study reports.

Weird Orbits of Pluto's Moons Caused By Huge Collision | Space

Cat

 

[darylcheshire]

What would happen if I parked my hypothetical spaceship at the barycenter of Pluto and Charon?

 

[Catastrophe]

It would probably remain there; Newton suggested that this would be the case, assuming no interaction arising from a visiting mssive object.

Cat

 

[DarkMatterMuncher]

The entire Pluto system is interesting on a wider level, but not least is the Pluto/Charon barycentre - which depends on the masses of dwarf planet and satellite - or are they joint dwarf planets?

Pluto's moon Charon sports a red polar cap that forms as seasons change | Space.com Forums

Cat

Ah, the Pluto-Charon system—what a fascinating cosmic duo! When we talk about the Pluto/Charon barycenter, we're essentially discussing the point around which both objects orbit each other. What makes this so intriguing is that the barycenter isn't located inside Pluto, as you'd typically expect with a planet and its moon. Instead, it sits in the space between them, which is a pretty big deal. This happens because Charon is relatively massive compared to Pluto—about 1/8th of Pluto's mass—so their gravitational dance is more like a partnership than a traditional planet-moon relationship.

Now, as for whether they're joint dwarf planets—that's a bit of a semantic puzzle. Officially, Pluto is classified as a dwarf planet, and Charon is considered its largest moon. But because of their unique barycenter and the way they interact gravitationally, some astronomers have playfully suggested they could be thought of as a "binary dwarf planet system." It's not an official classification, but it does capture the spirit of their relationship. They’re kind of like cosmic siblings, locked in a mutual orbit that blurs the line between planet and moon.

So, while the International Astronomical Union (IAU) hasn't given them the joint title, the Pluto-Charon system challenges our traditional definitions and reminds us that nature often defies our neat categorizations. It’s a humbling reminder of how much we still have to learn about the cosmos—and how wonderfully weird it can be.

 

[Helio]

Pluto’s other moons will greatly affect the barycenter’s location.

 

[Catastrophe]

Pluto’s other moons will greatly affect the barycenter’s location.

Helio, you know that I have the greatest respect for your knowledge of this subject generally. Of course I accept that the four tiny moons will have some effect, but on checking the comparative masses (see below) and the following:

All of the outer circumbinary moons are also close to mean motion resonance with the Charon–Pluto orbital period. Styx, Nix, Kerberos, and Hydra are in a 1:3:4:5:6 sequence of near resonances, with Styx approximately 5.4% from its resonance, Nix approximately 2.7%, Kerberos approximately 0.6%, and Hydra approximately 0.3%.[21

it seemed to me that the effect might not be very large.

Styx, Nix, and Hydra are thought to be in a 3-body Laplace orbital resonance with orbital periods in a ratio of 18:22:33.[18][19] The ratios should be exact when orbital precession is taken into account. Nix and Hydra are in a simple 2:3 resonance.https://en.wikipedia.org/wiki/Moons_of_Pluto#cite_note-resonance1-21[18][20] Styx and Nix are in an 9:11 resonance, while the resonance between Styx and Hydra has a ratio of 6:11.[c]

https://en.wikipedia.org/wiki/Moons_of_Pluto

Pluto's five moons, including Charon, have masses that range from a few millionths of Pluto's mass to roughly 12% of Pluto's mass. Charon, the largest, is about 12% of Pluto's mass, while the other four (Styx, Nix, Kerberos, and Hydra) are much smaller.

Here's a more detailed breakdown:

• Charon: Mass of approximately 158.7 ± 1.5 x 10^19 kg (about 12% of Pluto's mass).
  
  
• Styx: Mass of approximately 0.00075 x 10^19 kg.
  
  
• Nix: Mass of approximately 0.005 ± 0.004 x 10^19 kg.
  
  
• Kerberos: Mass information is not as readily available as for other moons, but it is known to be smaller than Nix and Hydra.
  
  
• Hydra: Mass of approximately 3.01 ± 0.30 x 10^16 kg.

It would be interesting if you can find any firm figures on the effects.

Cat

 

[Helio]

You make a fair point. It’s all about mass and proximity. But resonance can be problematic, too. Small perturbations over enough time will move objects out of L1. I recently read L1 isn’t all that stable typically, with L4 and L5 being more stable. Given the Trojan story, this might be true. I’m curious if this is the case.