Vesta

Vesta, the brightest asteroid of all, named after the Roman goddess of health.
It is the only asteroid visible to the naked eye. Discovered March 29, 1807 by Heinrich Olbers, Vesta was the fourth "terrestrial planet" to be discovered. Among asteroids, the second mass and the third in size. It orbits the Sun in 3.6 terrestrial years and its mean diameter is about 520 km. The composition of its surface is basaltic in nature. Vesta has a huge crater near its south pole. This huge rock of irregular shape, with no trace of water, has a core composed of iron. The enormous crater at the south pole of Vesta (460 km wide and 13 km deep), is the result of a collision. Astronomers believe that 5% of meteorites found on Earth come from this huge shock.
Vesta, with a mean diameter of 520 km, is much more massive than any other body in this region of the asteroid belt. Although Vesta is a huge asteroid, its oblong shape does not make him an object in hydrostatic equilibrium (it is not spherical), a necessary condition for the considered dwarf planet.
In July 2011, the Dawn spacecraft to Vesta has come to stay in orbit a year or so and then turn back on its engines to reach a much larger asteroid, Ceres, it will reach in 2015. This is the first time a vehicle reaches an object, the main asteroid belt, Vesta and Ceres are the two objectives of the mission.

Image: Vesta seen by the Dawn spacecraft in orbit since July 2011, Vesta alone accounts for 9% of the total mass of the asteroid belt. Photo taken by the probe while it was 5 200 km away in Vesta. Image Credit: NASA, JPL-Caltech, UCLA, MPS, DLR, IDA

The journey of the probe Dawn will enlighten us a little about the birth of our solar system and on planet formation.
After several delays, NASA launched the space probe DAWN bound asteroids Vesta and Ceres, the two largest known celestial bodies in the asteroid belt located between Mars and Jupiter.
Delta 2 rocket, fitted with nine boosters was slender, in the skies over Florida, Thursday, September 27, 2007 at 11:34 UTC. This ambitious NASA mission designed to orbit the probe Dawn around Vesta in 2011 and Ceres in 2015. To achieve these two asteroids, a gravity assist maneuver around Mars was necessary in 2009.
The study of these two items should allow a better understanding of the initial conditions of the solar system soon after its formation and understand the stages of planet formation. Dawn will travel a total of 5.1 billion km, 7 months evolve around each asteroid.
Overflights at low altitude are planned, at an altitude of 15 km to Vesta and Ceres to 40 km. Ceres and Vesta and protoplanets are formed at about the same time, when the formation of planets in the solar system, there are about 4.5 billion years. Vesta and Ceres are very different.

Vesta is a large rock of irregular shape, dry and rocky with a surface that appears to be composed of frozen lava. Ceres is almost round (diameter 960 km) and the poles may have frozen. Ceres has the distinction of having the dual status of dwarf planet and asteroid since 2006 as Pluto and Eris. The mission is scheduled to last until July 2015. This unusual journey is made possible by ion propulsion engines. The Dawn probe is equipped with cameras, an infrared spectrometer and a neutron detector and gamma rays. The energy of the solar panels of 19.8 meter wingspan will allow the operation of its three ion propulsion engines. "For me, it's really the first real interplanetary spaceship," said the chief engineer Marc Rayman. Dawn mission COST $ 357 million (252.7 million euros) excluding cost of launch by the Delta rocket.

Image: Vesta et les tailles comparées des astéroïdes. La mission de la sonde Dawn ("aurore" en anglais) est prévue pour durer 8 ans et son voyage de 5,1 milliards de kilomètres va nous renseigner sur les premiers instants de la naissance du système solaire, il y a 4,6 milliards d'années. Image © Nasa/JPL-Caltech/Ucla/MPS/DLR/IDA