Impact of Asteroids

Asteroids are small celestial bodies composed of rock and metal, that revolve around the Sun. Their size can vary: some asteroids are large and roughly spherical in shape, due to which they appear like miniature planets; while the others are small and irregularly shaped. The matter of these celestial bodies also differs. The asteroid 'Vesta', is believed to have a nickel-iron core, olivine mantle and basaltic crust, while the asteroid '10 Hygiea' is composed of carbonaceous chondrite. Most of the small asteroids are piles of rubble held together by gravity. Some asteroids supposedly have traces of amino-acids and other organic compounds, and it is assumed that the impact of asteroids on the Earth could have initiated life on the planet by seeding it with the necessary chemical substances.

Although, it is believed that the asteroids may have planted life on the Earth, they are capable of having catastrophic effect on the planet as well. Asteroids with a diameter of 5 to 10 meters, and energy equal to 15 kilotons of TNT, enter into the Earth's atmosphere approximately once every year; while, those with a diameter of over 50 meters enter the Earth's atmosphere approximately once in a thousand years. Their impact can be devastating if they hit the Earth, but they disintegrate in the upper atmosphere and most of the particles are vaporized, thus rendering them harmless.

In the distant past, our planet has experienced a massive climate change and large-scale extinction of animal and plant species, ascribed to the impact of some large asteroids on the planet. The exogenesis theory suggests that origin of life on the Earth must have been triggered by the impact of some asteroid, carrying organic chemicals needed to initiate life form. The Cretaceous-Tertiary extinction event, which led to the end of dinosaurs and the Permian-Triassic extinction event that led to the end of the Permian period finishing off 90% of the species on the planet, are believed to be the result of an asteroid impact on the Earth.

The craters on the solid bodies in the solar system, which were attributed to volcanic activities till 1960s, were actually formed due to the impact of celestial bodies. Researchers have determined that in the last 600 million years, 60 objects with a diameter of five km or more, have struck the Earth. Even the smallest of these object possessed energy of ten million megatons of TNT, and would have formed a crater, approximately 95 km in diameter, on the surface of our planet.

The Rio Cuarto craters in Argentina are believed to have formed due to the impact of asteroids that struck this area around 10,000 years ago. In 1490, ten thousand people reportedly lost their lives due to a hail of stones from the sky. This hail of stones is assumed to be result of the disintegration of a large asteroid, after it entered the Earth's atmosphere. In 1908, a mid-air explosion of an asteroid destroyed 80 million trees, within an area of 830 miles, near the Podkamennaya Tunguska River, in Siberia. In many cases, the sighting of a foreign body, such as an asteroid or a meteoroids is reported as a fireball in the sky.

Millions of asteroids will pass by the Earth in the years to come. Though, they are unknown now, they are detectable as they come closer to the planet. The Lincoln Near-Earth Asteroid Research (LINEAR) and the Near Earth Asteroid Tracking (NEAT) are projects initiated by NASA to detect asteroids or other such foreign bodies coming close to the Earth. The need of the hour is to develop an intercept system in space, to destroy or deflect foreign objects heading towards our planet, before they prove catastrophic.