Ion Engines Drive Dawn to Asteroids Vesta and Ceres

The Dawn spacecraft is on its way to asteroids Vesta and Ceres, powered by its ion engines. Principal investigator Chris Russell leads the international team behind it. He joins us for a conversation about this probe that will be the first to orbit two bodies other than Earth. Emily Lakdawalla's Q&A wonders if we could have visited Pluto decades ago, while Bruce Betts plays Santa Claus on this week's What's Up examination of the night sky with Mat Kaplan. All that and a new space trivia contest.