Small rocks enter the Earth’s atmosphere every single day. These are typically the size of a pebble and burn up quite harmlessly many tens of kilometers up into our atmosphere. At larger intervals of time, however, Earth is assaulted by much larger asteroids. On February 15th of this year at 9:20am local time, an asteroid estimated to weigh 11,000 tonnes entered the atmosphere over Chelyabinsk, Russia and subsequently exploded at a height of about 24 km, releasing the equivalent energy of 30 times that of the Hiroshima atomic bomb. The shockwaves that followed the bright explosion damaged upwards of 7,000 buildings and injured about 1,500 people. Now that everyone is only ever a few feet away from some sort of camera, the impressive event was extremely well documented. It is not, however, the first known event of its kind.
The Chelyabinsk meteor is the largest known object to have entered Earth’s atmosphere since what is known as the 1908 Tunguska Event. Meteor airbursts of this size occur every 100 years or so. The Tunguska Event luckily happened over a barren region in Siberia, where only very few eyewitnesses were reported to have seen a great flash of light and feeling a powerful shockwave that knocked them off their feet. The explosion may have been over 30 times more energetic than the Chelyabinsk meteor airburst. It registered on seismographs as an earthquake of 5.0 on the Richter scale and set the nightskies of Europe and Asia aglow for many nights. We can only theorise what may have happened had such an event occurred over a densely populated region, but the effects would most likely have been quite devastating. Later expeditions to the explosion site found entire forests of trees covering an area of 2,150 square kilometers completely scorched and knocked down from the blast.
Due to the remote location of this event, as well as the primitive state of our understanding of meteor behaviour at the time, a number of alternate theories have been proposed to explain the Tunguska Event. These range from a miniature black hole passing through the Earth to a giant pocket of natural gas being released from the Earth’s crust to Serbian inventor Nikola Tesla’s death ray experiment having gone awry. The meteor airburst theory remains the most scientifically supported one to date.
While these events are quite rare, it should be noted that the Chelyabinsk object was completely undetected before it exploded in our atmosphere. Perhaps the Universe is reminding us that we should keep a closer eye on it…