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NASA's Dawn becomes first spacecraft to orbit a dwarf planet

The Dawn space probe will take a much closer look at Ceres' mystery lights now that it is in orbit around the protoplanet.

Ceres and lights
Scientists hope to find an explanation for these bright spots. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

NASA's Dawn mission is celebrating a milestone today. The space probe successfully arrived at and went into orbit around the dwarf planet Ceres in the middle of its asteroid-belt home. It felt the pull of Ceres' gravity at a distance of about 38,000 miles out.

Launched in September 2007, Dawn has been on an adventure with the goal of peeking into the earliest history of the solar system by visiting the protoplanets Vesta and Ceres. Dawn arrived at the asteroid Vesta in 2011, gathering images and mapping it. Vesta was fascinating, but Ceres beckoned the mission forward.

Ceres -- the largest object in the asteroid belt between Mars and Jupiter -- has tempted scientists with its size (590 miles in diameter compared with Vesta's 330 miles) and mysterious bright spots.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," said Marc Rayman, Dawn chief engineer and mission director at NASA's Jet Propulsion Laboratory. "Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres, home."

This marks the first time a spacecraft has orbited a dwarf planet, according to NASA.

Dawn is now set to carry out its mission objectives, which includes investigating the role size and water play in the evolution of planets. Scientists are curious if Ceres may have seasonal polar caps made of water frost. They are all also interested in getting to the bottom of the bright-spot mystery. Dawn should help answer those questions. Going into orbit is just the first step in a new chapter of discovery.