科技英语新闻:NASA's Dawn spacecraft provides new images of asteroid Vesta

BEIJING, Aug. 2 (Xinhuanet) -- The first close-up pictures of the asteroid Vesta, a protoplanet that dates back to the early days of the solar system, were revealed Monday by NASA scientists.

The images were taken by the U.S. space agency's Dawn robotic probe, which is two weeks into a planned year-long survey of the second largest object in the main asteroid belt, located between Mars and Jupiter.

About twice the size of California, Vesta is second in size only to Ceres, Dawn's next target and, along with Pluto, one of just five known dwarf planets.

NASA is spending 466 million dollars to explore Vesta and Ceres during the course of a 10-year mission.

Images from Dawn show Vesta a surprisingly diverse terrain and several unexplained geologic features. Chaotic terrain near the south pole is dominated by a towering central peak and huge ripple-like grooves stretching around its equatorial belt. Bright spots, dark pits and craters are filled with unexplained streaks of black and white debris. Terrain north of the grooves is much more heavily cratered.

Scientists believe Vesta grew from a clump of gas and dust left over after the sun's birth some 4.65 billion years ago, a supernova explosion, which added radioactive materials to the growing body.

Dawn will spend about a year circling Vesta, tweaking its orbit and altitude using an innovative technology called ion propulsion system, chief engineer Marc Rayman with NASA's Jet Propulsion Laboratory in California said.

The ion propulsion system will enable Dawn to leave Vesta's orbit after a year of study and head off to Ceres, which is the largest object in the asteroid belt.