These are key in providing power for its ion propulsion system and for its instruments and on-board systems at a distance of almost 3 AU from the Sun. With its solar
arrays fully extended, the spacecraft is 19.7 meters (65 ft) long. The solar arrays have a total area of 36.4 square metres (392 sq ft). Credit: NASA/George Shelton
then. Vesta appears to have been hot and dry, like the
terrestrial planets, and experienced at least partial melting, whereas water seems to have played a role in keeping Ceres much cooler, so that it may be less evolved.
A battered world: Vesta revealed
Vesta, discovered by Heinrich Wilhelm Olbers on
29 March 1807, is named after the virgin goddess of
home and hearth in Roman mythology. Dawn was the
first spacecraft to visit Vesta, entering orbit on July 16,
2011, and successfully completing its fourteen month
survey mission of this fascinating body in late 2012.
Dawn’s instruments have revealed a rocky, battered world which reflects the violent early history of
the solar system. It accreted from the planetesimals
in the region and would perhaps have joined with
similar large planetary embryos to form a planetsized body, were it not for the gravitational influence
of massive Jupiter, which disrupted and prevented
planet formation in the main asteroid belt, an explanation for the plethora of bodies in this region today.
Representative of the type of bodies which eventually collided to form the Earth and other inner planets, it
is probably the last of its kind. Dawn has shown us good
evidence for the internal differentiation of Vesta, with a
thin crust and rocky (silicate) mantle overlying a metalrich (iron-nickel) core, estimated to be about 220km (136
miles) across. This layering, which is uncommon among
asteroids, is borne out by its mean density which is similar to that of our Moon, and not much less than that of
Mars (3.93 g/cm3). Differentiation would have occurred
as heating from radioac tive decay, large impacts, and
gravitational pressure melted parts of the protoplanet
as it grew. In melted zones heavier elements sank to the
center, while lighter materials rose to the surface. The
core is now solid, unlike that of the larger Earth which remains hot, thanks largely to radiogenic heating, the heat
released by the radioactive decay of certain elements.
False colour image showing the relief of Vesta’s south polar region and the
giant Rheasilvia impact basin with its central peak. Blue areas represent
lower elevation, while yellow and red areas show the highest elevations.
Credit: NASA/JPL-Caltech/ UCLA/MPS/DLR/IDA
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