The dwarf planet Ceres is only becoming more mysterious following investigations of the icy body by the Dawn Spacecraft. Launched in September 2007, this is the first spacecraft ever to explore any dwarf planet.

As Dawn approached Ceres, the spacecraft observed a pair of mysterious bright markings that puzzled astronomers.

Ceres is the largest member of the asteroid belt orbiting the sun between Mars and Jupiter, and it is one of five dwarf planets known in the solar system. Pluto, once known as the ninth planet, is the best-known of these bodies.

The Hubble Space Telescope (HST) observed Ceres in 2003 and 2004, creating the most-detailed images of the dwarf planet available before the arrival of the spacecraft on March 6. On March 10, mission controllers used Dawn to record new photos of the body with 9.5 times better detail than was possible using the HST. Data from the Hubble was examined, providing evidence of as many as 10 bright spots on the surface of the dwarf planet.

New color images of Ceres show a great deal of diversity in the materials present on the surface of the miniature world. The data suggests that Ceres may have once been geologically active.

"This dwarf planet was not just an inert rock throughout its history. It was active, with processes that resulted in different materials in different regions. We are beginning to capture that diversity in our color images," Chris Russell, principal investigator for the Dawn mission for Jet Propulsion Laboratory, said.

As Dawn approached the dwarf planet from its "night" side, the first images released may not be stunning from the point of view of aesthetics. However, they will provide astronomers with views of strange bright spots seen on the surface of the body during the days leading up to the encounter. No one is certain of their source, and while some are warmer than surrounding regions, others are cooler.

As the Dawn spacecraft headed toward its primary target of Ceres, the vehicle studied the asteroid Vesta, becoming the first observatory to orbit two bodies. Astronomers now believe the dwarf planet is composed of 25 percent water, compared with Vesta, which is extremely dry.

On April 23, Dawn will enter the main science phase of its mission, to be carried out from a distance of 8,400 miles from the dwarf planet.

"The bright spots continue to fascinate the science team, but we will have to wait until we get closer and are able to resolve them before we can determine their source," said Russell.

Study of Ceres could shed new light on mysteries surrounding the formation of the solar system, researchers believe.

Investigation of the new images from Ceres was profiled in the journal Nature.

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