4 Vesta
| Orbital characteristics | |
|---|---|
| Orbit type | Main belt |
| Semimajor axis | 2.362 AU |
| Eccentricity | 0.0895 |
| Orbital period | 3.63 year |
| Inclination | 7.14° |
| Physical characteristics | |
| Diameter | 516 km |
| Mass | 2.71×1020 kg |
| Density | 3.8 kg/m3 |
| Rotation period | 5 h 20 min |
| Spectral class | V |
| History | |
| Discoverer | H. Olbers, 1807 |
Vesta is the third-largest known main-belt asteroid, 525 km in diameter, discovered on March 29, 1807. Among the large asteroids, only Vesta has a surface of basaltic rock from ancient lava flows that may overlay an olivine mantle. This indicates that in the distant past Vesta likely differentiated into layers and underwent many of the same geological processes that the early Earth and Mars underwent. Dozens of Vesta-like asteroids are presumed to have existed at one time, but since then have been broken apart into families of smaller asteroids; nickel-iron asteroids are thought to come from the cores of such bodies, with stony ones coming from their crusts and mantles.
In 1996 the Hubble Space Telescope detected a huge crater on Vesta, 430 kilometers across and perhaps a billion years old. It is thought that this crater may be the source of the small V-type asteroids observed today. Vesta is scheduled to be visited by the Dawn Mission in 2010.
After the discovery of Vesta in 1807, no other asteroids were discovered for 38 years; the next was Astraea.