NASA today revealed the first close-up imagery of Vesta, one of the largest asteroids in our solar system.

The ion-propelled spacecraft Dawn, which took nearly four years to reach the 330-mile-wide space rock, recorded the photos and beamed them to Earth on July 24, 2011.

“Our patience is paying off very handsomely,” said engineer Marc Rayman of NASA’s Jet Propulsion Laboratory and member of the Dawn mission during a televised press briefing. “We’re now exploring one of the last uncharted worlds in the solar system.”

Vesta is the second most massive object in the asteroid belt and has a surface area twice that of the state of California. Researchers think the asteroid formed some 4.6 billion years ago, an age that makes its pockmarked surface a crucial record of the early solar system.

Although the asteroid may harbor evidence of an early supernova that irradiated its surface, Dawn’s controllers are focusing on big and obvious features for now.

One is a line of three craters that Dawn’s engineers called “the Snowman.” Another is a series of enormous grooves lining Vesta’s dusty equator.

Dawn mission leader and planetary scientist Christopher Russell of the University of California, Los Angeles thinks an ancient and catastrophic impact carved the grooves around Vesta. But he’s less certain about the appearance of the Snowman and other craters lined with black and white material.

“I haven’t seen anything like that before,” Russell said during the briefing.

Dawn snapped the images shown here from a distance of about 3,200 miles, but the spacecraft will soon descend to an orbit about 1,700 miles above the asteroid. NASA expects it to reach that orbit and begin its science mission in earnest on August 11, 2011.

Sometime in August 2012, the spacecraft will fire its engines and head toward Ceres, the biggest object in the asteroid belt. Planetary scientists think they may find evidence of a mud volcanoes on its surface and a liquid ocean below.

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