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The great planet debate

New suggestions for defining a planet would put Pluto and many other objects back on the list.

By Ashley Yeager

- More than 2 years ago

LAUREL, MD. — Ask planetary scientist Mark Sykes where NASA’s Dawn spacecraft is headed, and he will say it is on its way to the largest asteroid and the smallest planet.

POSSIBLE PLANETS Ceres (top) is thought of as a planet to some and Vesta (bottom) could be too.