The Dawn space probe has finally launched on its much delayed mission to explore the Asteroid Belt for clues on how the Solar System was formed.

The probe was launched from a Delta 2 rocket at Cape Canaveral after two delays that set the mission back over a month. It has now deployed its solar arrays and is beginning its seven-year mission.

"Dawn has risen, and the spacecraft is healthy," said mission project manager Keyur Patel of Nasa's Jet Propulsion Laboratory. "About this time tomorrow [Friday morning] we will have passed the Moon's orbit."

The probe will investigate Ceres and Vesta, the two largest objects in the Asteroid Belt between Mars and Jupiter. It will reach Vesta in late 2011 and go into orbit for seven months before heading to Ceres and arriving in February 2015.

Dawn will use an ion drive, which ionises xenon to produce low levels of thrust but can maintain acceleration for months at a time.

Scientists hope that the probe will reveal why some planets form and others fail due to lack of material.

The Asteroid Belt is thought to be a failed planet or possibly a planet that formed but was shattered by being struck by an outside body like a comet.