Vesta is the second-most-massive body in the asteroid belt and a genuine protoplanet: it melted early, separated into an iron core, rocky mantle and basaltic crust, and then simply stopped growing. NASA’s Dawn spacecraft orbited it in 2011-12 and mapped a battered world of ancient lava plains, deep troughs and one colossal impact basin, Rheasilvia, at its south pole.
It is the brightest asteroid in our sky - at its best it is faintly visible to the naked eye.
The central peak of the Rheasilvia basin rises roughly 20 km, rivalling Olympus Mons on Mars.
Roughly 1 in 20 meteorites that fall to Earth is a chip knocked off Vesta.
Meteorites with a return address
The HED meteorites - howardites, eucrites and diogenites - match Vesta’s surface spectrum so closely that scientists were confident of their origin decades before Dawn arrived. They are debris blasted out of the Rheasilvia basin. Vesta is the only asteroid we can study both from orbit and in the laboratory: we literally hold pieces of it.
Physical characteristics
Diameter
525 km
Dimensions
573 × 557 × 446 km
Mass
2.600e+20 kg
Surface gravity
0.25 m/s²
Density
3.46 g/cm³
Rotation period
5.34 h
Geometric albedo
0.42
Atmosphere and composition
Atmosphere
None.
Composition
Differentiated rock: an iron core, olivine mantle and basaltic lava crust - a planet in miniature.
Discovery
Discovered by
Heinrich Wilhelm Olbers
Year
1807
How
visual telescope search from Bremen
Missions
DawnNASA · Orbiter · 2007–2018 · completed
Powered by gentle ion engines, Dawn became the only spacecraft ever to orbit two different deep-space worlds: the asteroid Vesta (2011-2012) and the dwarf planet Ceres (2015-2018). It ran out of fuel in 2018 and remains in a stable orbit around Ceres.