One Mission, Two Remarkable Destinations
Dawn was a remarkable journey in both space and time, NASA’s first truly interplanetary spaceship. The mission featured extended stays at two very different extraterrestrial bodies: giant asteroid Vesta and dwarf planet Ceres. Both small worlds reside in the debris-strewn main asteroid belt between Mars and Jupiter.
Dawn’s super-efficient ion propulsion system allowed the spacecraft to spend fourteen months in orbit at Vesta before cruising on to Ceres, where it will remain in perpetual orbit.
Ceres and Vesta are two of the earliest objects discovered in the asteroid belt. Together, they account for about 40 percent of the mass of all the tens of thousands of inhabitants in the asteroid belt—indeed, Ceres is so massive it was reclassified as a dwarf planet in 2006. They were chosen for close study because they are so different. Vesta is more like the rocky worlds of the inner solar system, and Ceres more like the icy moons of the outer solar system. By exploring them both, scientists are getting a snapshot of the conditions during the first 10 million years after the birth of our solar system.
When our solar system was first forming, materials in the solar nebula varied with their distance from the Sun. As the distance increased, the temperature dropped. Rocky bodies formed closer to the Sun, and icy bodies formed farther away. Vesta is a terrestrial world, rocky and dense like Mars and Mercury.
Ceres, on the other hand, is a world of both rock and ice. With a rigid protective crust as dark as asphalt, a less rigid interior, and a solid core, Ceres’ lower density indicates ices are a major part of its composition beneath the surface.
After chasing down Ceres for more than two years, the Dawn spacecraft arrived safely in March 2015 and moved into orbit to begin humanity's first-ever exploration of a dwarf planet. As the mission concluded its science orbits, we have learned far more about mysterious Ceres, and its bright spots have captured our collective imagination.
Major Science Achievements
- First to orbit a main-belt asteroid
- First to reach a dwarf planet
- Explored the two largest planetesimals