Spacecraft to examine massive asteroids

THE US spacecraft Dawn, due to launch on Sunday, will take a close look at two massive asteroids to try to penetrate the mystery of our solar system's origins 4.6 billion years ago.
By examining the two celestial bodies Ceres and Vesta in the asteroid belt between Mars and Jupiter, scientists hope the unmanned Dawn probe will shed light on the earliest moments in the birth of the solar system.

The National Aeronautics and Space Administration (NASA) says the Dawn mission should provide a better understanding of the building blocks that formed the terrestrial planets and how the two "protoplanets'' followed different evolutionary paths.

The deep-space explorer, measuring 1.64 meters (yards) long and 1.27 meters (yards) wide when its solar array is retracted, is equipped with a high-definition camera and two spectrometers to study the two massive asteroids.

Ceres, discovered in 1801, has a spherical shape and has a diameter of about 960 kilometers (596 miles).

Scientists believe it may have a layer of thick ice under its crust, covering a rocky core.

Ceres was classified in 2006 as a "dwarf planet'', according to a new definition by astronomers to describe asteroids in the solar system.

The decision by the International Astronomical Union was the result of a debate about the status of Pluto, which is now classified as a dwarf planet along with Ceres and another celestial body, Eris.

Vesta, discovered in 1807, is smaller than Ceres but the third largest asteroid in the solar system.

With a diameter of 520 kilometers (323 miles), Vesta has a rocky suface without a trace of water and a hot interior.

Scientists are especially interested in the enormous crater on the south pole of Vesta, 460 kilometers (285 miles) wide and 13 kilometers (8 miles) deep, which is believed to be the result of a major collision.

Astronomers estimate that five percent of all meteorites found on Earth are the result of this gigantic jolt.

"What we're interested in is what our ancestors were like,'' said Christopher Russell, Dawn's principal investigator and a professor of geophysics and space physics at the University of California.

"We're interested in what these early bodies did and how they evolved because those are the building blocks basically of the Earth,'' Mr Russell said.

In an eight-year mission, Dawn is scheduled to enter orbit around Vesta in October 2011, proceed to Ceres in May 2012 and then begin orbiting Ceres in February 2015 - travelling a total distance of 5.1 billion kilometers.

The spacecraft is equipped with innovative ion propulsion engines, which consume relatively little fuel and only accelerate at a gradual pace.

The engines use an electrical charge to accelerate ions from xenon fuel.

After having cancelled the Dawn project previously, NASA revived the mission in 2006 after an investment of 449 million dollars.

It is the ninth mission out of 10 planned in NASA's Discovery program that employs unmanned vehicles to explore space, often focusing on asteroids.