In the early 19th century, Giuseppe Piazzi and a group of astronomers called the Celestial Police turned their telescopes towards the sky in search of a missing planet between Mars and Jupiter. What they discovered instead was something unexpected—not a lone planet but many smaller objects that would later be classified as the first asteroids. Today, scientists use data from spacecraft missions to get a better look at the surface of asteroids and study their compositions.

Hear Dr. Jennifer Scully, a NASA scientist and member of the Dawn mission team explain how our understanding of asteroids evolved over the last two centuries.