As dawn is breaking on the UK tomorrow the Dawn spacecraft will have begun its year-long orbit of the asteroid Vesta. Data will start being gathered in August.
Dawn is a ground-breaking mission, the first to orbit a main-belt asteroid (main-belt asteroids orbit the Sun at a distance between Mars and Jupiter). These asteroids are thought to be the remains of a failed planet that could not grow because of interference from Jupiter’s large gravitational field. We can learn a great deal about what the early solar system was like from these asteroids as they are remnants of the first building blocks of the planets.
After orbiting Vesta (the only asteroid visible with the naked eye, due to its highly reflective surface) the mission will continue to the asteroid Ceres (the largest asteroid in the solar system at 960 km in diameter).
The mission objectives are given on the JPL/NASA website:
- “first that it captures the earliest moments in the origin of the solar system enabling us to understand the conditions under which these objects formed.
- Second, Dawn determines the nature of the building blocks from which the terrestrial planets formed, improving our understanding of this formation.
- Finally, it contrasts the formation and evolution of two small planets that followed very different evolutionary paths so that we understand what controls that evolution.”
Vesta is thought to be the source of many achondritic meteorites that reach earth: Howardites, Eucrites and Diogenites ( commonly known as HED meteorites). These rocks are around 4.5 billion years old and would have been ejected from Vesta when it was hit by another object. We are currently studying xenon and krypton in two eucrites. These have different oxygen isotope ratios to other eucrites though the rest of their chemical and geological make-up is the same. This may mean that they did not originate on Vesta but on another asteroid that formed and evolved in a similar way. Results from our work will be presented at the Meteoritical Society Meeting in Greenwich this August and at the Lunar and Planetary Science meeting in Houston in early 2012.
Any data the Dawn mission gathers will add to current understanding of the formation and evolution of the early solar system. It may also help determine whether the majority of HED meteorites do actually originate on Vesta.