METERORITE EVENTS IN RECORDED HISTORY.

 

The TUNGUSKA explosion occurred near the Tunguska River in Russia northwest of Lake Baikal on June 30 1908. Luckily, it was a sparsely populated area with only 3 reported deaths. However, it flattened 80 million trees over an area of 2150 Sq Mtrs.

This blast is attributed to a meteor air burst in the atmosphere of a stony meteoroid about 50-60 meters across. It approached Earth at a speed of 27 Km/Sec. No crater was found as the object was supposed to have deteriorated at an altitude of 5 to 10 Km instead of directly hitting the earth. This is the largest impact event in the Earth’s recorded history.

An explosion of this size could have destroyed a large metropolitan area.

In the more recent times on 15^th February 2013, a 20-meter asteroid entered the earth at a velocity of 19 Km/Sec near CHELYABINSK in Russia. It weighed 12000-13000 tons. The meteor exploded in the air at a height of 30 Km. The atmosphere absorbed the bulk of the explosion's shock, creating a large shockwave equal to a 400-500 kiloton TNT blast, some 30 times the power of 30 Hiroshima bombs.               

This object approached the earth undetected before its atmospheric entry because its source direction was close to the sun. About 1500 people were injured as the shockwave hit 6 cities and damaged 7200 buildings.

Among these, the Chelyabinsk explosion was the most recent and mankind is very lucky that both in this case as well as the Tunguska event the meteors exploded in the atmosphere. Otherwise, a 12000 ton body hitting any area with a velocity of 19 Km/ Sec can cause a devastating impact.

These 2 events in recorded history clearly prove that such events are likely to happen again. We have to be particularly worried about Chelyabinsk-like events because the Chelyabinsk meteor approached the earth undetected as it came from the direction of the Sun. This is despite the NASA’s observations on NEO.  

A NEO (Near Earth Objects) Observations program had been launched by NASA and the EU in 1998 and is tracking the NEO’s. A NEO is by definition all those natural bodies that approach up to a distance of 1.3 AU (Astronomical Unit the distance from Sun to Earth 151 million KM).

If a NEO crosses the earth’s orbit and if it is larger than 140 meters, then it is considered a PHO (Potentially Hazardous Object). Most of the PHOs known are asteroids but a few are Comets.  

There are over 30500 known NEO Asteroids, and over 100 NEO Comets. NASA is continuously tracking these bodies.