Dawn – The journey to the beginning of the Solar System! It’s a fairly ambitious mission, as are most of NASA’s missions at the moment. Firstly the spacecraft uses ion propulsion, a technology tested on Deep Space 1 but never before used for a dedicated science mission. Secondly Dawn has not one but two targets. The large asteroid or even protoplanet, Vesta and then the dwarf planet Ceres. The spacecraft will go into orbit around Vesta, happily do some science for a while, break orbit and then go to orbit Ceres!
Dawn launched back in September 2007 atop a Delta II rocket. It’s been in the cruise ever since, giving short bursts of ion propulsion to refine it’s orbit. Now after nearly 4 years she’s almost arrived, ready to hop into orbit.
Vesta is the largest asteroid in the Solar System (Ceres is larger but is termed a dwarf planet) it’s about 530km across and is estimated to contain 9% of the mass of the asteroid belt, so it’s a pretty hefty object. It’s thought to be differentiated, that is it’s so big so that heavier elements, like iron, fall towards the centre and lighter elements are found nearer the surface. This is the same way that Earth’s core formed.
We already know a fair bit about Vesta surprisingly. About 1 billion years ago Vesta was hit by an asteroid that’s left a small crater. This threw out lots and lots of debris, and quite a bit of this has fallen to the Earth. These meteorites have the fancy name of Howardite-Eucrite-Diogenite (HED) meteorites. Evidence from these meteorites show that Vesta is between 4.43 and 4.55 billion years old and reveals that Vesta has a history of extensive igneous processes. Infact the meteorites are very similar to magmatic rocks found on the Earth.
The mission at Vesta is to develop our understanding of how the Solar System formed and in particular what role water played in planetary evolution. Vesta and Ceres both reflect what the early Solar System was like, something we can’t figure out here on Earth because of all the geological activity the Earth is still going through. Continue reading