BEIJING, July 6 (Xinhuanet) -- NASA is ready to launch this weekend a spacecraft that will search for clues about the solar system while traveling to the asteroid belt between Mars and Jupiter for a rendezvous with two of its largest asteroids.

    The Dawn spacecraft will first encounter Vesta, the smaller of the two bodies, four years from now. In 2015, it will meet up with Ceres, which carries the status of both asteroid and, like Pluto, dwarf planet.

    "We're trying to go back in time as well as to go out there in space," said planetary scientist Christopher Russell of University of California, Los Angeles, who is heading up the mission.

    Dawn is set to blast off Sunday afternoon from Cape Canaveral, Fla., on a Delta II rocket. The launch caps a tumultuous effort in which the 344 million U.S. dollar mission was killed last year because of cost overruns and technical problems, then brought back online after NASA appeals.

    Vesta and Ceres are thought to have evolved in different parts of the solar system more than 4.5 billion years ago around the same time as the formation of the rocky planets including Mercury, Venus, Earth and Mars. Scientists believe the asteroids' growth was stunted by Jupiter's gravitational pull and never had the chance to become full-fledged planets.

    Vesta, which measures 326 miles across, is dry and pocked with a deep impact crater in its southern hemisphere. By contrast, Ceres, about twice as large as Vesta, has a dusty surface covered by what appears to be an ice shell and may even contain water inside.

    When Dawn reaches each asteroid, it will orbit each body, photographing the surface and studying the asteroid's interior makeup, density and magnetism. Pictures and data will be sent back to Earth.

    Dawn will be powered by ion propulsion instead of conventional rocket fuel, making it more fuel-efficient and allowing it to cruise between the asteroids and lower itself to about 125 miles above the surface to study them in depth.

    (Agencies)