Sept. 27 (Bloomberg) -- NASA'S Dawn probe launched into clear skies from Florida's Cape Canaveral this morning, headed for the heart of the asteroid belt, where it will hunt for clues about the formation of the solar system.

A Delta II rocket carrying Dawn blasted off from the Kennedy Space Center about 50 miles (80 kilometers) east of Orlando at 7:34 a.m. New York time in a live National Aeronautics and Space Administration telecast. The launch came after a spate of weather-related delays in recent months.

The golf-cart-size Dawn will take about four years to reach the orbiting ring of rubble between Mars and Jupiter, 250.9 million miles (403.8 million kilometers) to 371.8 million miles from Earth, according to the Planetary Society Web site.

Once there, the 2,600-pound (1,200-kilogram) probe will scan the two biggest objects in the asteroid belt for clues that may help scientists find links between the rocky inner planets of the solar system and the gaseous bodies farther away, NASA said.

The largest object in the belt, the dwarf planet Ceres, roughly 600 miles in diameter, and the next-largest, a spherical asteroid called Vesta, are regarded as building blocks left over from the solar system's formation about 4.5 billion years ago. Ceres appears to contain water in the form of ice and may have an atmosphere, while Vesta bears some characteristics of rocky planets closer to the sun, such as Earth.

`Extraterrestrial Contrasts'

``Visiting both Vesta and Ceres enables a study in extraterrestrial contrasts,'' Christopher Russell, a University of California, Los Angeles, professor and principal Dawn investigator, said on NASA's Web site. ``One is rocky; the other may very well be icy. Yet these two diverse bodies reside in essentially the same neighborhood.''

Ceres is similar to the icy moons of the outer solar system and may offer insight into how planets evolve, NASA said. As Dawn orbits, it will measure mass, shape, topography and tectonic history, as well as mineral composition. It will also look for any substances that could hold water, the key to life.

NASA calls Dawn the ``Prius of space,'' thanks to its three weak, super-efficient engines, something akin to the power plant in the Toyota Prius hybrid. After jettisoning the Delta rocket, Dawn will ignite one of three ion-propulsion engines.

An electrical current, fed by solar panels, will run through xenon gas, the same element used in camera flashbulbs and car headlights. The xenon ions generated by the basketball-size engines will create a low, persistent thrust, too slight to even propel a skateboard on Earth but enough to push Dawn to 5,500 miles an hour (8,800 kilometers an hour) after a year, using just 15 gallons (57 liters) of fuel.

Dawn's mission will last eight years. It will be the first spaceship to orbit and explore two celestial bodies on a single trip. The probe will reach Vesta in four years and spend about seven months circling the asteroid.

It will then begin its three-year journey to Ceres, spending about the same amount of time orbiting the dwarf planet before ending its mission in 2015.

To contact the reporter on this story: Demian McLean in Washington at dmclean8@bloomberg.net.

Last Updated: September 27, 2007 10:31 EDT