The solid ellipse is Dawn's orbit around Ceres, XMO7, ranging from 22 miles (35 kilometers) to 2,500 miles (4,000 kilometers). We described above that Dawn's peridemeter gradually moves south. Dawn's ion engines have enabled this interplanetary spaceship to accomplish a journey unique in humankind's exploration of the solar system. No other spacecraft has ever orbited two extraterrestrial destinations, and Dawn's mission to do so would have been impossible without ion propulsion. Next month we will discuss what will happen to Dawn's orbit after the mission ends.