Astronomy: Asteroids

Asteroids are chunks of rock, metal, or both that were once part of smallish planets but were destroyed after collisions. Most orbit the Sun between Mars and Jupiter, but some get near the Earth. The biggest, Ceres, is far smaller than the Moon but still big enough to be round and has undergone differentiation. CORRECTION: In the episode, we say that 2010 TK7 is 800 km away. However, 2010 TK7 stays on average 150 million kilometers from Earth, but that can vary wildly. Sorry about that!