2013

Chelyabinsk Fireball

Earth is constantly being bombarded by space debris. More than 60 tons (4.5 million kilograms) of cosmic dust rains down on our planet every day, and larger material enters our atmosphere as well, from rocks the size of pebbles to solid chunks of iron tens of meters across. When the smaller objects encounter the Earth’s atmosphere, they are quickly heated by friction and burn up high above the surface. These meteors (also called “shooting stars”) often arrive in clusters that correspond to Earth’s passage through the orbit of a periodic comet. For example, the mid-August Perseid meteor shower comes from tiny pieces shed off the comet Swift-Tuttle.

Occasionally, however, bigger pieces of comets or asteroids enter the Earth’s atmosphere, where they either explode as bright fireballs or survive to the surface, forming craters and leaving behind meteorites. For example, NASA used ground-based and satellite monitoring stations to catalog more than 550 fireball events between 1994 and 2013, representing the impact of objects from about 3 feet (1 meter) to 60 feet (18 meters) in size. Nearly all those objects burned up in the atmosphere before striking the surface.

The largest fireball event in recent history occurred on the morning of February 15, 2013, when an asteroid estimated to be around 60 feet (18 meters) in size and traveling at more than 40,000 miles (64,000 kilometers) per hour exploded about 19 miles (30 kilometers) above the Russian city of Chelyabinsk. Numerous security cameras and dashboard cameras captured the low-angle vapor trail and brilliant ensuing fireball, making it one of the most photographed impact events ever. The upper-atmospheric airburst explosion created a shock wave that shattered windows in thousands of buildings and injured about fifteen hundred people.

Reconstruction of the path of the impactor (also known as a “bolide”) revealed that it originated in the main asteroid belt between Mars and Jupiter, and recovery of meteorite fragments revealed that it was likely a piece of a larger parent body that was knocked off in a much earlier asteroid collision.

Like the Tunguska explosion of 1908, the Chelyabinsk fireball was a roughly once-per-century impact event. The grazing impact angle and resulting high atmosphere explosion likely prevented greater injuries and damage, and the extensive media coverage of the event has helped to make people more aware of the fact that the Earth resides in a cosmic shooting gallery.

Still from a dashboard camera video, showing the vapor trail and fireball created by the explosion of a small asteroid above Chelyabinsk, Russia, on February 15, 2013.