NASA's Dawn spacecraft has sent home the clearest photos to date of the dwarf planet Ceres and the white spots on the extraterrestrial world's surface, which has been puzzling scientists, appeared as bright as ever and even more defined than before.

The images were among the first snapshots taken by the probe on June 6 since it got into its latest mapping orbit 4,000km above the extraterrestrial world's surface. The spacecraft, which is now in its second mapping orbit, will be at this altitude until June 28 when it will drop into a lower orbit.

By August, the probe will take observations 1,450 kilometers from the dwarf planet's surface. The probe will drop further at a height of 375 km in December. At this Low Altitude Mapping Orbit, Dawn will have a resolution of 35 meters per pixel, which could potentially yield very detailed images of the dwarf planet.

The pictures are the highest resolution images of the surface of Ceres to date but mission scientists are still puzzled with what the bright spots really are. The spots are located in a crater measuring about 90 km wide.

One of the most feasible guesses is that the mysterious feature's brightness can be attributed to the presence of salt or ice. Dawn principal investigator Chris Russell said that the bright spots are distinct from anything that has been seen in the Solar System but while much about this feature remains unknown, scientists hope that as Dawn gets closer to Ceres, they will be able to learn more about these bright spots.

Dawn is equipped with a thermal images and a neutron detector that can detect presence of water and these could also help resolve the mystery of the bright spots.

"The science team is working to understand their source. Reflection from ice is the leading candidate in my mind, but the team continues to consider alternate possibilities, such as salt," Russell said. "With closer views from the new orbit and multiple view angles, we soon will be better able to determine the nature of this enigmatic phenomenon."

NASA launched Dawn in 2007 with the goal of approaching and studying the protoplanet Vesta and the dwarf planet Ceres, located in the asteroid belt between planets Jupiter and Mars.

Scientists think that Ceres may have been on its track to becoming another big planet such as Mars and Earth but its growth has stalled. They hope that by studying this alien world, they will be able to gather valuable data on the conditions of the early Solar System.

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