Photo Gallery: Asteroids and Comets

One of the youngest and best-preserved impact craters on Earth, Meteor Crater formed about 50,000 years ago when a 100-foot-wide (30-meter-wide) meteor weighing 100,000 tons slammed into the Arizona desert at an estimated 12 miles (20 kilometers) a second. The resulting explosion exceeded the combined force of today's nuclear arsenals and created a 0.7-mile-wide (1.1-kilometer-wide), 650-foot-deep (200-meter-deep) crater.