In trying to solve the riddle of Sedna’s “missing moon,” scientists Scott Gaudi, Krzysztof (Kris) Stanek and colleagues at the Harvard-Smithsonian Center for Astrophysics took measurements that have cleared up the mystery by showing that a moon wasn’t needed after all. Sedna is rotating much more rapidly than originally believed, spinning once on its axis every 10 hours. This shorter rotation period is typical of planetoids in our solar system, requiring no external influences to explain.

“We’ve solved the case of Sedna’s missing moon. The moon didn’t vanish because it was never there to begin with,” said Gaudi.

The research was submitted to The Astrophysical Journal Letters for publication and is posted online at

While these data solve one mystery of Sedna, other mysteries remain. Chief among them is the question of how Sedna arrived in its highly elliptical, eons-long orbit.