Sedna's such a curious little guy and it took me a while to see what was so interesting about it. Then I realized it's a fossil, and the creature it's a fossil of is our solar system. But you can't reconstruct the image of a creature with only one of its bones, so without more fossils, our solar system can look like any one of a few slightly different creatures.
It's a puzzle and Sedna is an important piece that lets us know that we're missing something. There's nothing more exciting in science than evidence that you have more to discover.