Moon around Kuiper Belt Object

UncleJosh writes "Today's NY Times (free reg rq'd) has a story about the first Kuiper Belt Object (KBO) with a moon, 1998 WW31. The hubble telescope has been used to get information about the size and orbit of the moon. Seems lots of things have moons. Coming more than 20 years after the discovery of Pluto's moon Charon the discovery of a KBO with a moon also follows the discovery of asteroid Ida's moon Dactyl and other moons of asteriods."

Comments

Re:Too bad this isn't in the main section

[Anonymous Coward]

I think the story of Pluto is that the people that originally "discovered" it thought it was bigger than it actually is. They discovered the presence of a massive object by its gravitational effects on Neptune, and thought it was large enough to be considered a planet. It was later discovered that it was smaller than originally thought. We still call it a planet today because we've been calling it one all along. It's the largest (discovered) Kuiper Belt object, but if we had just discovered it recently, it's likely that it would not be considered a planet.

Re:Too bad this isn't in the main section

[Anonymous Coward]

This poses major questions though, about what exactly is a planet.

The definition of a "what is a planet" is pretty flexible. As long as it admits the 9 bodies that were accepted as planets for historical reasons and rules out the rest, you've got a working definition.

Is Jupieter a planet?

Yes. See above.

What about Pluto?

Yes. See above. The definition is designed to fit the facts we want, not the other way around.

This is not surprising

[n-baxley]

Two boides are attrackted while spinning in orbit around another, larger body. They start to co-orbit. That's physics people. Why do we have to call the smaller of these two objects a moon? These are just two asteroids who are orbiting each other. That's it. Sheesh.

This IS surprising (physics)

[Spamalamadingdong]

Two boides are attrackted while spinning in orbit around another, larger body. They start to co-orbit. That's physics people.

Two bodies approach each other from "infinity", and somehow they lose enough energy and/or angular momentum in their encounter to wind up in mutual orbit. How's that? What's the mechanism for dissipating energy, or transferring angular momentum from motion of the bodies around their center of mass to spin of the bodies themselves (Earth and Luna are doing this in reverse, but very slowly; far too slowly to capture anything).

Since you've set yourself up as the physics expert, perhaps you'd like to explain that to all of us. You'll probably get a publishable paper out of it too, so it's not like it isn't worth the work.