When the planetoid Sedna was discovered last year, astronomers noticed that it had a very slow rotation speed, only turning once every 20 days. One way to slow the rotation of a planet is through the interaction of a moon, but detailed observations of Sedna with Hubble failed to turn up any evidence of a satellite. New observations by astronomers with the Harvard-Smithsonian Center for Astrophysics have revised Sedna’s rotation speed to once every 10 hours, which is what you’d expect for an object this size. No moon is necessary.