Puzzling Sedna

Last February, astronomers first discovered Sedna, an object a bit small than our moon, orbiting way out towards the edge of our solar system. Sedna just doesn't fit with any other object in our solar system. It's a bit too small to be called a planet, but if we don't call it a planet, we could not call Pluto a planet by the same measure. Yet, Sedna is too large and too round to be an astroid. The tilt and shape of Sedna's orbit is unlike any of the nine traditional planets, and Sedna's origin is still totally unknown. It may have formed with Earth and the traditional planets, or it may have formed somewhere else before it was captured by our sun's gravity. An article in The Washington Post explains the many mysteries of Sedna, discussing lots of good astronomy along the way. Link.