30th June 1908: A huge explosion flattens over 800 square miles of Siberian forest in the remote region of the Podkamennaya Tunguska River. In the absence of detailed information, wild theories abound – it might have been a miniature black hole, perhaps even an alien spacecraft in difficulties. However, the general view is that it was an asteroid or comet fragment entering the Earth’s atmosphere and bursting in mid air, possibly a piece of Encke’s Comet; witness accounts mention repeated sounds like artillery, which perhaps means that Siberia was under bombardment by a series of separate fragments.
13th August 1930: There are reports of three large explosions in the Brazilian rain forest near the Peruvian border – local inhabitants talk of burning trees and a widespread ash cloud. Observatory records suggest that these were caused by one or more asteroid impacts coinciding with the peak of the annual Perseid meteor shower.
2nd February, 1932: Explorer and intelligence officer St. John Philby (father of double agent Kim Philby) discovers pieces of meteoric iron littering the remote Arabian desert in the Empty Quarter or “Rub’ al Khali”. Later, three impact craters are found in the sand at Wabar, which suggests that an asteroid exploded in mid-air over the Arabian Peninsula (with the force of a 16-kiloton nuclear weapon, approximately), maybe as recently as 1891.
16th July, 1994: The first of many fragments of comet Shoemaker-Levy 9 crash into Jupiter, the comet having been captured by the gas giant’s gravity in the 1960s or ’70s and fallen victim to Jupiter’s crushing tidal forces. Over the next few days, big pieces of comet slam into the planet’s atmosphere one after the other, creating vast dark spots which are clearly visible by telescope from Earth. The largest of these pieces (fragment G), impacting on 18th July, smashes with a force equivalent to 6,000,000 megatons.
15th February, 2013: A meteor explodes high over the Urals in Russia, creating a massive fireball, damaging buildings in six cities across the region and injuring over a thousand people (mainly cuts caused by shattering window glass). This happens 16 hours before asteroid 2012DA14 is due to pass by Earth; NASA tells us, however, that the two events are not related, the trajectories of the two objects being very different.
The meteor that lit up the skies over Chelyabinsk last week exploded with a force of nearly 500 kilotons and is estimated to have had a diameter of up to an estimated 56 feet. However, near-earth asteroid 2012DA14 which skimmed past us the same day has a diameter of around 160 feet and would have made a correspondingly bigger bang, had it collided with Earth instead – it would not have been in the Shoemaker-Levy class (thankfully!) but might have done considerably more than create smoke trails and smash windows.
To those who say that global warming is the greatest long-term threat to the human race, I think we might have to agree to disagree. In the Solar System’s great meteoric shooting gallery – going by a century’s worth of occasional impacts and near misses – it seems we have been relatively fortunate. So far, anyway.
Some useful links:
Wikipedia on the Tunguska Event:
Article on the Armagh Observatory website about the Brazilian meteors of 1930:
Wikipedia on Wabar impact craters:
Wikipedia on Shoemaker-Levy 9:
Wikipedia on the Russian meteor event of 2013: