POLL: Sedna, planet or debris?

[Happy43]

I find it ironic that each time a rock is found, it becomes "the TENTH PLANET"...

In June 2002 Quaoar became the tenth planet by the way, not Sedna..

See:

http://www.gps.caltech.edu/~chad/quaoar/

Paul

 

[Happy43]

http://www.theage.com.au/articles/2002/10/07/1033538894512.html

Another Quaoar article -

At least it's bigger than Quaoar...
I hate to quote CNN (they are terrible at getting science news right), but... here goes:

http://www.cnn.com/2004/TECH/space/03/14/planet.discovery/index.html

Paul

 

[DrPizza]

Originally posted by: Brucmack

Second: Unless Newton made a huge mistake, the earth exerts a gravitational force on the moon, and the moon exerts an exactly equal force on the Earth. (people have trouble with this fact. They can "repeat for every force there's an equal and opposite force" ad nauseum, but they don't believe it) Since this results in a net force on the earth, it would be wrong to say that the earth continues in a path, unaffected by the moon, while the moon simply revolves around the earth.

Yes, this is correct, and that's why we get tides. But that doesn't make the earth-moon pair a binary system. It's a simple matter of the weight ratio... The earth is so much more massive than the moon, the centre of mass of the system is actually inside the earth. So the earth can't orbit about that point. Sure, it gets pulled by the moon, but it's insignificant compared to the effect the earth has on the moon.

With a system like Pluto-Charon, they are much closer to being the same mass (I think Pluto's only about twice as massive?) This means that the centre of mass is between the two bodies, and they orbit about this point, making it a binary system. As such, Charon isn't a moon in the traditional sense, only because Pluto is considered a planet and Charon is a smaller object in the vicinity.

I'm curious to learn more about this. (I love analogies): take a bowling ball, attach a golf ball to it with a yard long piece of coat hanger, and throw it spinning through space. The bowling ball will follow more or less a straight path, with the marble revolving around it. But, there will be a slight wobble to the path of the bowling ball. Now, on the earth, we have the tides. Do the tides completely negate the wobble the earth has in its path? I wouldn't think it would, but I'm not certain. I do realize though that the orbits of the earth and other planets are actually chaotic over large amounts of time because of interactions with each other.

 

[Matthias99]

It's a simple matter of the weight ratio... The earth is so much more massive than the moon, the centre of mass of the system is actually inside the earth. So the earth can't orbit about that point.

"A four-ounce bird simply cannot carry a two-pound coconut!"

I don't buy this argument. You can certainly rotate an object (mathematically, at least) about a point internal to itself. IMHO, it's certainly valid to say that the Earth and Moon are a "binary system", just a rather asymmetrical one. The tides, AFAIK, do not entirely counter the moon's pull on the Earth, but they do account for some of it, certainly dampening the movements of the 'solid' part of the earth a good bit.

Sure, it gets pulled by the moon, but it's insignificant compared to the effect the earth has on the moon.

It's *small* compared to the effect the earth has on the moon (relative to the path of both around the Sun), but not insignificant. A 1% 'wobble' is certainly noticeable on a planetary scale (assuming the numbers given above are close to accurate). It's not like, say, the Sun and the Earth, where the center of mass of the system is (for all practical purposes) the center of the Sun.