Just What is Ceres? Dawn is About to Find Out

NASA's Dawn spacecraft has the protoplanet Ceres in its sight, and soon will have a close encounter with this unusual alien world. Still, before Dawn get's there, it may help to answer some questions such as "what exactly is Ceres?"

Far off in our solar system, you can find the "asteroid belt," a ring of giant chunks of space rock, ice and dust, that separates the orbits of Mars and Jupiter. The core of this main belt extends an average breadth of 113.4 million miles, but understandably thins and expands at certain points around the Sun.

And within this field of space rock you can find two titanic asteroids - notable fractions of Earth's total size.

The asteroids, named Ceres and Vesta, are the largest known asteroids in the belt and are even visible with the naked eye, having first been identified by astronomers in the early 1800s.

"These two bodies are much more massive than any body yet visited in this region of space and are truly small planets," the Dawn mission team, at NASA's Jet Propulsion Laboratory (JPL), wrote in their mission statement.

Stunningly, Ceres, the largest asteroid at about 600 miles in diameter, may have a thin, permanent atmosphere, setting it apart from other massive rocks. Experts like to classify bodies like Ceres and Vesta as "protoplanets" - small planet-like objects that were in the process of becoming true terrestrial planets before Jupiter's heavy gravitational influences on the asteroid belt disrupted their formation. (Scroll to read on...)

Still, this makes them perfect snapshots of planet formation halted forever in time.

"When Dawn visits Ceres and Vesta, the spacecraft steps us back in solar system time," the JPL team said.

Since the Dawn probe launched in 2007, it already paid a visit to Vesta, which proved a dry and metallic wasteland. In contrast, experts believe that Ceres will be exceptionally primordial, showcasing a different and far more wet formation path.

As of Dec. 1, Dawn was only 740,000 miles from Ceres and closing in fast. The probe is expected to reach its destination near the start of the new year.

"Now, finally, we have a spacecraft on the verge of unveiling this mysterious, alien world," Marc Rayman, chief engineer and mission director of the Dawn mission, said in a statement. "Soon it will reveal myriad secrets Ceres has held since the dawn of the solar system."

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