Dawn, the first spacecraft to orbit a body in the asteroid belt, will depart Vesta on Aug.26 for its next target, the dwarf planet Ceres.
Since its arrival at Vesta last July, the spacecraft has provided researchers with the first orbital analysis of the giant asteroid. Dawn has revealed that Vesta more closely resembles a small planet or Earth's moon than another asteroid. Scientists now see Vesta as a layered, planetary building block with an iron core, mantle and crust. They believe it formed the same way as the other terrestrial planets.
After concluding its exploration of Vesta this month, the spacecraft will pull off an even more impressive first. It will leave Vesta and fly to the dwarf planet Ceres. Scientists believe that Ceres is very primitive and wet, and they suspect that it may have frosty polar caps. This unprecedented maneuver will make Dawn the first spacecraft to orbit two different bodies after leaving Earth.
Dawn's ion-propulsion engine makes it possible for the spacecraft to accomplish this extraordinary maneuver. Its solar arrays collect power from the sun to ionize atoms of xenon gas. These ions are expelled silently out the back of the spacecraft by a strong electric field, producing a gentle thrust. The weightless, frictionless conditions of space flight allow the spacecraft to continuously gain speed and slip into and out of orbit as gently as it has been moving since its launch.
This mission was named Dawn because it was designed to study objects dating from the dawn of the solar system 4.6 billion years ago when our solar nebula collapsed and micrometer-sized particles began to stick together and clump into larger bodies. By studying two different bodies, Ceres and Vesta, scientists hope the mission will provide data that will give them a better understanding of the origin and evolution of the solar system.