ScienceShot: Dawn Closing In on Asteroid Vesta

On 16 July, NASA's Dawn spacecraft will for the first time go into orbit around one of the asteroid belt's big "protoplanets," a rocky body so large that eons ago it began to evolve geologically along the same path taken by Earth. At a press conference today, Dawn team members showed their latest image of the 529-kilometer-diameter asteroid Vesta (left), which has more than twice the detail that the Hubble Space Telescope was ever able to muster from Earth orbit (right). From 154,000 kilometers—one-third the distance from Earth to the moon—scientists still can't say much about what they are looking at. Many of the fuzzy features must be impact craters formed in collisions with smaller asteroids over more than 4 billion years. The largest impact, near the south pole, is thought to have blown off bits and pieces of Vesta that ended up falling on Earth as meteorites. Instruments onboard Dawn should be able to confirm the meteorite-Vesta link and let Dawn researchers better understand another body that melted and separated into crust, mantle, and metallic core. After a year in Vesta's orbit, Dawn will spiral away on its ion engines to another, icier protoplanet, Ceres.

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