NASA's 'Dawn' enters orbit around Ceres

The probe Dawn entered orbit around Ceres on Friday after a seven-and-a-half year voyage, NASA said, making it the first dwarf planet ever to be visited by a spacecraft.

Ceres is the largest object in the asteroid belt between the planets Mars and Jupiter, which contains rocky remnants of the creation of the sun and planets some 4.5 billion years ago.

The dwarf planet is the last and final stop for Dawn, which earlier visited the asteroid Vesta, taking photographs of its surface over the course of a year.

Dawn will now spend 16 months mapping Ceres, which is named after the Roman goddess of agriculture and harvests. The spacecraft is to come to within 378 kilometers (235 miles) of the surface at its closest approach - approximately the distance at which the International Space Station orbits the Earth.

Unanswered questions

Ceres has a diameter of about 1,000 kilometers (600 miles), and is thought to have a rocky core surrounded by an icy mantle. Scientists will be hoping to find out whether there is or used to be an underground ocean in Ceres' interior, as has been proposed by some.

Photographs beamed back by Dawn to Earth during its approach showed two puzzling bright spots inside a crater whose cause scientists are also eager to learn about, surmising that they could be signs of possible ice or salt. The spacecraft's instruments will also be used to confirm whether Ceres' surface is still active and venting previously spotted plumes of water vapor.

The mission to Ceres costs $473 million (434 million euros). The spacecraft flew 4.9 billion kilometers (3.1 billion miles) to reach its final destination.

Another dwarf planet, Pluto - which was once considered the ninth planet of the Solar System before being demoted in 2006 - is also due for a visit from a NASA spacecraft, New Horizons, this summer.

tj/sms (AP, AFP)