Mysterious dwarf planet Ceres now in the spotlight

LOS ANGELES (AP) - The mysterious dwarf planet Ceres is ready for its close-up.

Located in the asteroid belt between Mars and Jupiter, Ceres was the largest unexplored space rock in the inner solar system.

But that distinction ended Friday, when NASA's Dawn spacecraft arrived after a nearly eight-year journey, which included a stopover at the asteroid Vesta. It's now circling the dwarf planet on a 16-month mission.

Five things to know about Ceres:

THE DISCOVERY

Ceres was spotted on New Year's Day in 1801 by Italian monk and astronomer Giuseppe Piazzi who was searching for a star. It was the first object discovered in the asteroid belt, a zone littered with rocky debris left over from the formation of the sun and planets 4ˆ½ billion years ago.

THE NAME

Piazzi named the object "Ceres Ferdinandea" after the Roman goddess of harvest and in honor of King Ferdinand IV of Naples and Sicily. Other astronomers shortened it to Ceres. The word cereal also has its origins in the goddess' name. The chemical element cerium, discovered in 1803, was named after the celestial Ceres.

THE IDENTITY CRISIS

Located about 250 million miles from the sun, Ceres was deemed a comet when it was first discovered. Then it was promoted to a planet and later downgraded to an asteroid. Since 2006, it has been classified as a dwarf planet like Pluto, the one-time ninth planet. Dwarf planets are spherical in shape like planets, but they share the same celestial neighborhood with other similar-sized objects.

THE BRIGHT SPOTS

Ceres - with a diameter of about 600 miles - is thought to have a rocky core surrounded by an icy mantle. Long ago it might have harbored an underground ocean. As Dawn approached Ceres, it sent back images of a pair of puzzling bright spots inside a crater. Scientists think the shiny dots may be exposed ice or salt.

THE MISSION

Launched in 2007 and powered by ion propulsion engines, Dawn will make the first close-ups of a dwarf planet, which won't begin until mid-April when the spacecraft emerges from Ceres' shadows.

Dawn will study Ceres for 16 months from varying altitudes, getting as close as 235 miles above Ceres' surface, or the distance of the International Space Station above Earth. The spacecraft will take sharper images of the mysterious spots and use its instruments to confirm whether Ceres' surface is still active and spewing plumes of water vapor.

This summer, another NASA spacecraft dubbed New Horizons will make the first visit to the dwarf planet Pluto.

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Online:

Dawn mission: http://dawn.jpl.nasa.gov/

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