The above image is an artist's concept of Dawn with asteroid Vesta (left) and Ceres (right). The proximity of Vesta to Ceres is not to scale, but does make a pretty picture. Image Credit: NASA
The Dawn mission is described as a journey to the beginning, or the dawn, of the Solar System, which is estimated to be over 4.5 billion years ago. Dawn's "time travel" is accomplished by the study of the small bodies that orbit the sun in the large region between the orbits of Mars Jupiter. We call this region the asteroid belt and it contains many thousands of these bodies. They formed at the same time and in similar environments as the bodies that grew to be Mercury, Venus, Earth, and Mars; those described as the rocky planets. Scientists think that the asteroids were potential planets that never had the opportunity to grow because of the gravitational influence of massive Jupiter. The asteroids, sometimes called minor planets, contain clues that reveal the conditions and processes acting at the Solar System’s earliest epoch. By investigating two very different asteroids, Ceres and Vesta, the Dawn mission seeks to unlock some of the mysteries of planetary formation.
The Dawn team chose to study Ceres and Vesta because they are two of the largest inhabitants of the main asteroid belt. They survived the collisional environment of the region and have remained intact since their formations. What's more, evidence shows that they each have distinct characteristics; so, each must have followed a different evolutionary path. Vesta appears to be dry, evolved, and differentiated with surface features ranging from basaltic lava flows to a deep crater near its southern pole. In contrast, Ceres has a dusty, clay-like surface and evidence of water, which has led scientists to suspect the presence of a thick water-ice mantle. Vesta’s physical characteristics reflect those of the inner planets, whereas Ceres’ are more like the icy moons of the outer planets. By studying these contrasts and comparing these two minor planets, scientists will develop an understanding of the transition from the rocky inner regions to the icy outer regions of the Solar System.
The Dawn mission marks the first time a spacecraft orbits a body in the main asteroid belt and the first time a spacecraft orbits two targets, enabling a detailed and intensive study of both. Dawn uses the same suite of instruments to gather comparative data on Vesta and Ceres. Aboard the spacecraft, the science payload consists of two cameras, a visible and infrared mapping spectrometer to reveal the surface minerals, and a gamma ray and neutron spectrometer to determine the elements that make up the outer parts of the asteroids. The spacecraft also will be used to measure the gravity field, thereby revealing details of these asteroids’ interiors. With the data from these systems, scientists will study surface features and the complex and varied landscapes, gaining valuable new insights into the internal structure of these ancient worlds. What role did size have in determining how planets evolved throughout the Solar System? How did water affect the process of planetary formation? Data gathered during the Dawn mission will help scientists uncover the answers to these and other questions.
Dawn’s journey to the asteroid belt, which spans about eight years from launch to completion of data return, is made possible by ion propulsion. Initially tested and proven successful on NASA’s Deep Space 1 mission, this innovative technology is now applied for the first time in the design and implementation of a dedicated scientific space flight with the Dawn mission. Ion propulsion allows Dawn to undertake a bold and important mission that would be unaffordable—and even impossible—with a more conventional propulsion system. Two large solar panels, stretching approximately 19.7 meters (65 feet) from tip to tip, collect energy from the distant Sun. Within the ion engine, the energy then ionizes the onboard fuel, xenon, accelerating the ions—which, in turn, accelerate the spacecraft.
Educational activities for space enthusiasts of all ages are available at the Dawn mission Web site. For more information visit: http://dawn.jpl.nasa.gov.
And now, some mission management particulars...
Dawn is the ninth Discovery mission in NASA’s Science Mission Directorate and is a collaborative partnership of the University of California, Los Angeles; Jet Propulsion Laboratory; Orbital Sciences Corporation; Los Alamos National Laboratory; German Aerospace Center; Max Planck Institute for Solar System Research; Italian Space Agency; and Italian National Institute of Astrophysics. Dawn outreach materials are developed under contract by Mid-continent Research for Education and Learning (McREL), Denver, Colorado.
Launched September 2007, the Dawn spacecraft and the mission team are hard at work and currently studying Vesta. In the next Dawn installment, what we have learned from Dawn so far. In the mean time, learn more about the Dawn mission at: http://dawn.jpl.nasa.gov.