Dawn Arrives: NASA Spacecraft Orbits Ceres

NASA's Dawn probe arrived at the massive asteroid known as Ceres last Friday morning (Mar 6), making history as the first manmade spacecraft to achieve orbit around what astronomers call a "planetoid," or dwarf planet.

If you were to plug the word "asteroid" into an image search engine, you'd likely find yourself facing numerous photos of lumpy space rocks that look nothing like Ceres does.

A stunning 600 miles in diameter, Ceres is a perfectly round little world, almost like an incredibly small planet as it floats alone in space. Astronomers have long concluded that Ceres and another massive body in the Asteroid Belt, known as Vesta, are likely planets that were never given a chance to fully develop, as their growth was disrupted by the the immense gravity of nearby gas giant Jupiter.

"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), previously wrote in their mission statement.

Ceres alone is so large that NASA's experts have suspected it could even boast an incredibly thin atmosphere of its own.

"Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet," Marc Rayman, Dawn chief engineer and mission director at JPL, recently explained.

This technically puts Ceres in the same class as Pluto, which was demoted from its status as a true planet by the International Astronomical Union (IAU) back in 2006.

And after looking at the stunning photos delivered by Dawn as it drew closer to Ceres, you really can't blame them for their decision. Both Vesta, which Dawn visited back in July 2011, and Ceres are incredibly large and planet-like - not quite like moons, but certainly nothing like other terrestrial planets in this solar system (Earth, Mars, etc.)

But regardless of what astronomers call it, "after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres,' home,'" Rayman said.

"We feel exhilarated," added the Dawn mission's principle investigator, Chris Russell. "We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives."

Over the next few months, Dawn will position itself more snugly in its orbit around the planetoid, snapping photos all the while and launching analyses of things like atmosphere, topography, and the true nature of a few mysterious bright spots on Ceres' surface.

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