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An undated artist rendering released by NASA shows the NASA Dawn spacecraft in orbit around the giant asteroid Vesta. After spending a year examining Vesta, Dawn is poised to depart and head to another asteroid, Ceres, where it will arrive in 2015.(AP Photo/NASA)

Next and final stop: The biggest object in the asteroid belt.

After spending a year gazing at a giant asteroid, NASA's Dawn spacecraft on Wednesday began the cruise toward an even bigger target, a voyage that will take nearly three years.

Ground controllers received a signal from Dawn that it successfully spiraled away from the asteroid Vesta and was headed toward the dwarf planet Ceres.

The departure was considered ho-hum compared with other recent missions, think Curiosity's white-knuckle "seven minutes of terror" dive into Mars' atmosphere.

Firing its ion propulsion thrusters, Dawn gently freed itself from Vesta's gravitational hold Tuesday night. Since its antenna was pointed away from Earth during the manoeuvr, NASA did not get confirmation until the next day.

It was "smooth and elegant and graceful," said chief engineer Marc Rayman of the NASA Jet Propulsion Laboratory, which manages the $466 million mission.

Launched in 2007, Dawn is on track to become the first spacecraft to rendezvous with two celestial bodies in a bid to learn about the solar system's evolution.

Dawn slipped into orbit last year around Vesta and beamed back stunning close-ups of the lumpy surface. Its next destination is Ceres.

Vesta and Ceres are the largest bodies in the asteroid belt between Mars and Jupiter that's littered with space rocks that never quite bloomed into full-fledged planets. As cosmic time capsules, they're ideal for scientists trying to piece together how Earth and the other planets formed and evolved.

With its rugged exterior, complete with grooves, troughs and pristine minerals, and iron core, Vesta acts more like an "almost planet" than garden-variety, lightweight asteroids.

Vesta was "on its way to planethood if it continued to grow," said chief scientist Christopher Russell of the University of California, Los Angeles.

Scientists expect a different world at Ceres. Unlike the rocky, pockmarked Vesta, the nearly spherical Ceres has a dusty surface with an icy interior. Some think it may even have frost-covered poles.

"Almost everything we see at Ceres will be a surprise and totally different from Vesta," Russell said.

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Follow Alicia Chang at http://twitter.com/SciWriAlicia .