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mikeemmert
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Mike Brown's team of astronomers has discovered a second moon for 2003 EL61:<br /><br />http://www.gps.caltech.edu/~mbrown/2003EL61/#moon<br /><br />The second moon is about 0.2% of the mass of Santa. It's orbit is inclined about 40 degrees to the orbit of the first moon.<br /><br />In the article, Mike Brown figures that Santa's moons were formed much like Earth's, via a collision with another object. This makes sense.<br /><br />Santa gets my vote (and Mike Brown's, too) as the strangest object in the outer solar system. It's big, 32% of the mass of Pluto, and spins at a dizzying rate of one revolution in 3.9 hours. This distorts it into the shape of a Jacobian ellipsoid (as best as they can tell) that is somewhere around twice as long as it is wide.<br /><br />Much more bizzarre is it's density, somewhere around 3 times the density of water. It's made out of stone! This itself is evidence of a huge collision.<br /><br />[Disclaimer: I am responsible for the following material. Mike Brown may or may not agree, I don't know.]:<br /><br />Some of you may have read my post, "UB313 is the Lost Moon of Triton". I think the flyby of a binary with the second object being as massive as Triton is the only way Triton could lose enough energy to get into orbit around Neptune.<br /><br />I have done some gravity simulations of flybys of binaries composed of two Triton-sized objects past Neptune. Indeed, the binary often comes apart; one goes into orbit around Neptune and the other gains energy and goes into orbit around the Sun.<br /><br />Sometimes, however, the binaries collide. What seems to make the difference is the orientation of the two objects at closest approach. If they are lined up, so that the centers of the objects and the center of Neptune are in a straight line, then the binary will separate and one will go into orbit (unless they're going too fast or something). But if one follows another,