Rogue Asteroid - Part 2

Welcome to the second part of this mini-series, Rogue Asteroids.
In the previous part, we learned about the family of asteroids.
In case you missed it, Click here to read Part One.

In this part, we will learn more about the history of asteroids associated with earth. In simple language, the history of Asteroid impact and near misses.
The most staggering incident that comes to you is obviously the K-T extinction, where an Asteroid size of Manhattan hit the Earth near Florida causing massive chaos and ultimately killing over 80% of life on Land. Including the mighty dinosaurs.
But there are other incidents too, let us learn more about other Impact Events.

Illustrative image of K-T Extinction Impact Event

An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect. However, when large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry by burning the object with resistance from the atmosphere. Smaller objects are likely to burn off during the entry, large objects have the possibility of surviving the entry and land on the surface. These objects hit the surface at such speed that they create Craters on the surface. These Impact craters and structures are dominant land-forms on many of the Solar System's solid objects and present the strongest empirical evidence for their frequency and scale.

Crater left by an Impact Event

Impact events appear to have played a significant role in the evolution of the Solar System since its formation. Major impact events have significantly shaped Earth's history, have been implicated in the formation of the Earth-Moon system, the evolutionary history of life, the origin of water on Earth and several mass extinctions. The KT Extinction we discussed was caused by a prehistoric Chicxulub impact, 66 million years ago.

During recorded history also we have had numerous impact events, with some occurrences causing deaths, injuries, damages to property or other significant localized consequences.

The best-known incident in modern history was the Tunguska Event. On the morning of June 30, 1908, a large explosion occurred near the Tunguska River in Russia. The explosion over a sparsely populated area flattened an estimated 80 million trees over the area of around 2000 sq km of forest along with three reported human casualties. Despite such magnitude of explosion, no crater was found. It was thought that the object must have been disintegrated around 5 kilometers above the surface of the Earth. 

Scientists have estimated the size of the object around 50 to 90 meters in diameter and impact energy around 30 Megatons of TNT. That’s enough to wipe out the entire New York State.

Flattened Forrest by Tunguska Event

In February 1947, another Meteorite hit earth in Sikhote-Alin Mountain, Russia. The event happen in daylight and was witnessed by many people. It was later estimated that the Meteorite weighed about 100,000 kilograms and was made out of Iron. Luckily the impact site was far in forest and did not account for any human loss.

Sikhote Meteorite

In the dark morning hours of January 18, 2000, a fireball exploded over the city of Whitehorse, Yukon Territory at an altitude of about 26 km, lighting up the night like day. The meteor that produced the fireball was estimated to be about 4.6 m in diameter, with a weight of 180 tonnes.

Many impact events occur without being observed by anyone on the ground. Between 1975 and 1992, American missile early-warning satellites picked up 136 major explosions in the upper atmosphere. On November 21, 2002, edition of the journal Nature, Peter Brown of the University of Western Ontario reported on his study of U.S. early warning satellite records for the preceding eight years. He identified 300 flashes caused by 1 to 10 m meteors in that time period and estimated the rate of Tunguska-sized events as once in 400 years.

With all these smaller and not so harmful impacts we can easily assume that Asteroid/Meteorite Impacts are not a life-ending Threat. Why don’t you check the next event?

On August 10, 1972, a fireball was witnessed by many people in the sky as it moved north over the Rocky Mountains from the U.S. Southwest to Canada. The size of the object was estimated around the size of an average suburban house. It can be easily established that the object could have ended its life in a Hiroshima-sized blast. However, the lucky us survived as there was no explosion. Analysis of the trajectory indicated that it never came much lower than 58 km off the ground, and the conclusion was that it had grazed Earth's atmosphere for about 100 seconds, then skipped back out of the atmosphere to return to its orbit around the Sun.

Fireball Seen over Rocky Mountains

Another major impact was not so far in time, it came in 2013. A near-Earth Asteroid of size approximately 20 m entered Earth's atmosphere over Russia. Due to its high velocity and shallow angle of atmospheric entry, the object exploded in an air-burst over Chelyabinsk Oblast, at a height of around 30 kilometers The bulk of the object's energy was absorbed by the atmosphere, with total kinetic energy before atmospheric impact estimated from infra-sound and seismic measurements to be equivalent to the blast yield of 400–500 kilotons of TNT, range – 26 to 33 times as much energy as that released from the atomic bomb detonated at Hiroshima. 

The object was undetected before its atmospheric entry, in part because its entry direction was close to the Sun. Its explosion created panic among local residents, and about 1,500 people were injured seriously enough to seek medical treatment. All of the injuries were due to indirect effects rather than the meteor itself, mainly from broken glass from windows that were blown in when the shock wave arrived, minutes after the superbolide's flash. Some 7,200 buildings in six cities across the region were damaged by the explosion's shock wave, and authorities scrambled to help repair the structures in sub-freezing temperatures

Air-burst left behind by Chelyabinsk Meteorite

These are major events where asteroids have collided with Earth, and the scariest thing is none of them were detected prior to Impact.

In the next part, we will discuss the two NEO Asteroids that are on their way to Earth and are estimated to be here by Early April 2020.

Click here to read Part Three.

~Heisenberg