Thanks to ions: Deep in the asteroid belt is a rock the size of Arizona. It's called Vesta, it's the second biggest asteroid in the band of rubble between Mars and Jupiter, and in July it got a visitor: the Dawn spacecraft, which settled into orbit around Vesta, where it will remain for a year, studying what is one of the oldest objects in the solar system. Dawn traveled to Vesta in a whole new way: ion propulsion, which relies on a stream of xenon ions to nudge a spacecraft along on a gentle but steadily accelerating glide. Goodbye, heavy, traditional fuel and hello, asteroid. When Dawn is done with its work, it will puff its way out of orbit and head for Ceres, the solar system's largest (Texas-size) asteroid, and repeat the same surveillance. One ship, two stops not half bad.