On Friday at 2:25 p.m. EST, asteroid 2012 DA14 passed within 28,000 kilometers of Earth, the closest encounter with a near-Earth object since systematic tracking operations began in the 1990s. This is roughly 13 times closer than the distance from Earth to the Moon, and the effect of Earth's gravitational pull on 2012 DA14 will alter its orbit, shortening its orbit around the Sun by 51 Earth days.
The asteroid has a diameter of 45 meters, a mass of 130,000 metric tons, and passed by at a velocity varying between 20,000 and 30,000 kilometers per hour.
While scientists ruled out the possibility of an impact earlier this week, such an asteroid could cause significant damage if it collided with Earth. Asteroids of similar size caused the Tunguska event in Siberia in 1908 and the Meteor Crater event in present-day Arizona about 50,000 years ago.
Below are brief overviews of the three most common types of asteroids. 2012 DA14 is an S-type asteroid.