Vesta

Vesta , in astronomy, fourth asteroid to be discovered. It was found in 1807 by H. Olbers. It is the third largest asteroid, with a diameter of c.326 mi (525 km). Its average distance from the sun is 2.36 astronomical units , and the period of its orbit is 1,325 days. Vesta is the only asteroid that can be seen with the naked eye; it can be seen only when it is in the right position in the sky relative to the earth and sun, namely, when it is at opposition and perihelion simultaneously.

Vesta is geologically different from the other large asteroids. Images taken by the Hubble Space Telescope show a basaltic surface indicative of ancient lava flows originating from a molten interior and a giant crater, about 285 mi (460 km) across and 8 mi (13 km) deep, that may go all the way through the crust to expose the mantle. The crater is thought to have resulted from a collision with another celestial body, the impact tearing out large chunks of Vesta that formed a distinctive class of small asteroids, some of which have reached earth as meteorites . Alternatively, they all may have originated from the breakup of a large parent body early in the history of the solar system. These hypotheses were made more credible in 1999 when the space probe Deep Space 1 spectroscopically analyzed the small asteroid Braille and found it to be akin in composition to Vesta.

Vesta The third largest (after Ceres and Pallas) solar system asteroid (No. 4), diameter 526 km; approximate mass 3 × 10²⁰ kg; rotational period 5.342 hours; orbital period 3.63 years. It was imaged in 1995 by the Hubble Space Telescope and appears to have a basaltic crust overlying an olivine mantle, indicating that differentiation has occurred.

Vesta Asteroid 4, the fourth asteroid to be discovered, by H. W. M.Olbers in 1807. Its mean diameter is 530 km, similar to that of Pallas. Vesta's mass is 3 × 10²⁰ kg and its mean density is 3.9 g/cm³. Its orbit has a semimajor axis of 2.361 AU, period 3.63 years, perihelion 2.15 AU, aphelion 2.57 AU, and inclination of 7 °.1. Vesta's colour changes slightly as it rotates every 5.34 hours, indicating that its surface is not uniform in composition. The Hubble Space Telescope has shown bright and dark features as small as 80 km across on Vesta, suggesting a geologically diverse terrain with an exposed mantle, ancient lava flows, and impact basins. The average albedo is 0.38. Vesta's spectrum is characteristic of the mineral pyroxene, common in lava flows. Vesta may be a source of the eucrite meteorites and some other small asteroids. It is sufficiently different from other asteroids to be assigned a special class, V (for Vesta). Its apparent mean magnitude at opposition is 6.5, but at particularly favourable oppositions it can reach magnitude 5.5, the only asteroid bright enough to be visible with the naked eye.