Discovered in 1802 by Heinrich Olbers, 4 Vesta – located in the asteroid belt – is a dry, differentiated object with signs of resurfacing and intense meteorite impact. Vesta is a unique object formed during the early stages of the solar system 4.56 billion years ago. It is also thought to be the source of the howardite-eucrite-diogenites (HED) meteorites.
As part of NASA Discovery Program, the Dawn spacecraft was launched in September 2007 with three scientific drivers: (1) to capture the earliest moments in the origin of the solar system enabling us to understand the conditions under which these objects formed; (2) to determine the nature of the building blocks from which the terrestrial planets formed; and (3) to contrast the formation and evolution of two small planets that followed very different evolutionary paths so that we understand what controls that evolution. The two small bodies chosen for this mission were 4 Vesta and Ceres 1, both of which are thought to be surviving protoplanets.
Vesta reached Dawn on 16 July 2011. In this week’s issue of Science Russell et al. have confirmed that Vesta is a differentiated surviving protoplanet; that the Vesta-family asteroids and HEDs were most likely produced from material ejected from a large impact to Vesta’s south pole; and found Vesta to have sufficient core radius (107-113 km) to reach the internal melting temperatures to segregate iron. Dawn will leave Vesta in August 2012 and arrive at Ceres in February 2015. For more details, see
- Dawn at Vesta: Testing the Protoplanetary Paradigm, Russell et al. (2012), Science, 336, 684
- Dawn, NASA/JPL website
- NASA Discovery Program
[Catarina Ubach & Sarah Maddison]