APOD: Fifth Moon Discovered Orbiting Pluto (2012 Jul 16)

[orin stepanek]

An interesting fact about Pluto's relationship with Neptune from wiki

and other dynamical effects keep Pluto's orbit stable, safe from planetary collision or scattering.

Relationship with Neptune
Orbit of Pluto—polar view. This 'view from above' shows how Pluto's orbit (in red) is less circular than Neptune's (in blue), and how Pluto is sometimes closer to the Sun than Neptune. The darker halves of both orbits show where they pass below the plane of the ecliptic.Despite Pluto's orbit appearing to cross that of Neptune when viewed from directly above, the two objects' orbits are aligned so that they can never collide or even approach closely. There are several reasons why.

At the simplest level, one can examine the two orbits and see that they do not intersect. When Pluto is closest to the Sun, and hence closest to Neptune's orbit as viewed from above, it is also the farthest above Neptune's path. Pluto's orbit passes about 8 AU above that of Neptune, preventing a collision.[59][60][61] Pluto's ascending and descending nodes, the points at which its orbit crosses the ecliptic, are currently separated from Neptune's by over 21°.[62]

This alone is not enough to protect Pluto; perturbations from the planets (especially Neptune) could alter aspects of Pluto's orbit (such as its orbital precession) over millions of years so that a collision could be possible. Some other mechanism or mechanisms must therefore be at work. The most significant of these is that Pluto lies in the 3:2 mean motion resonance with Neptune: for every three of Neptune's orbits around the Sun, Pluto makes two. The two objects then return to their initial positions and the cycle repeats, each cycle lasting about 500 years. This pattern is such that, in each 500-year cycle, the first time Pluto is near perihelion Neptune is over 50° behind Pluto. By Pluto's second perihelion, Neptune will have completed a further one and a half of its own orbits, and so will be a similar distance ahead of Pluto. Pluto and Neptune's minimum separation is over 17 AU. Pluto comes closer to Uranus (11 AU) than it does to Neptune.[61]

The 3:2 resonance between the two bodies is highly stable, and is preserved over millions of years.[63] This prevents their orbits from changing relative to one another; the cycle always repeats in the same way, and so the two bodies can never pass near to each other. Thus, even if Pluto's orbit were not highly

[Moonlady]

I'm surprised you even saw Pluto at all.

Hey, I just saw it with my binocular 10x25 clearly! And I wouldnt need that, if I am not near-sighted

Moonlady, Pluto is too faint too see with binoculars that size. And I don't think a 3-inch telescope will be large enough to see Pluto, either.

Explaining irony isn't fun

[Raven]

Red alert. Incoming Pluto fans ready to beat the planet semantics horse again. Protect the horse!

It does seem strange: here we are, a planet with one moon; and there Pluto is, a "non-planet" with FIVE moons.

Is Pluto not a planet because it "hasn't cleared its orbit"? Of, say, Neptune?

But see Orin's explanation. That's only if we view Pluto's orbit two-dimensionally, as though it occurred in the same plane/ecliptic as Neptune's -- which in fact it doesn't. It occurs in a different plane, tilted from the ecliptic, and what other masses share its orbit in that plane?

Other than its five moons, that is?

I think the "orbit-clearing" definition needs clarification for orbits in such different planes.

Hey, I just saw {Pluto} with my binocular 10x25 clearly! And I wouldnt need that, if I am not near-sighted

Wellll, I'm far-sighted, so I had to pull my reading/magnifier glasses away from my nose a little bit....

[Beyond]

Wellll, I'm far-sighted, so I had to pull my reading/magnifier glasses away from my nose a little bit....

That doesn't work for me. I'm not far sighted enough to see Pluto.

[Raven]

That doesn't work for me. I'm not far sighted enough to see Pluto.

Tsk, in the spirit of a true Beyonder, you could have tried standing on your toes atop a footstool.

Yeah, well, maybe sometimes you'd have to wait for that pesky ISS to move out of the way....

[Beyond]

That doesn't work for me. I'm not far sighted enough to see Pluto.

Tsk, in the spirit of a true Beyonder, you could have tried standing on your toes atop a footstool.

Yeah, well, maybe sometimes you'd have to wait for that pesky ISS to move out of the way....

It's just that in this physical realm, i just can't see as far as Pluto. Perhaps if conditions were just right, with a brand new super nova off in the distance behind Pluto... Nah! I still wouldn't be able to see Pluto because of the brightness. Oh, well. Guess I'll just have to wait until someone makes more Mickey Mouse cartoons.

[Raven]

It's just that in this physical realm, i just can't see as far as Pluto.

You can see a whole lot farther than Pluto, viz. any stars you see in the night sky.

Perhaps if conditions were just right, with a brand new super nova off in the distance behind Pluto... Nah! I still wouldn't be able to see Pluto because of the brightness. Oh, well. Guess I'll just have to wait until someone makes more Mickey Mouse cartoons.

I didn't think Mickey's dog was all that bright. Or even Goofy....

[Beyond]

I didn't think Mickey's dog was all that bright. Or even Goofy....

Exactly That's why i can't see it.

[Raven]

I didn't think Mickey's dog was all that bright. Or even Goofy....

Exactly That's why i can't see it.

... but the reason you can't see Mickey's dog is that, having buried it all in the backyard, he now rules the underworld of wealth.

Hence the term "plutonian".

(Whereas you'll note the moon Charon wasn't named "Goofy". And so on for the other four.)

The dead giveaway? If the Pluto with five moons was canine, he'd be CHASING them!