The planet Earth has a long and violent history of collisions with extraterrestrial bodies such as asteroids and comet nuclei. Several of these impacts have been large enough to cause major environmental changes, causing mass extinctions and severe alterations to weather patterns and geography. Every day the Earth is bombarded by debris from space, but the vast majority of objects entering the atmosphere are tiny, and burn up long before they reach the ground. However, larger bodies will penetrate deeper into the atmosphere, and can detonate with tremendous explosive force. The object that devastated 2000 square kilometres of Siberian forest in 1908 was only 60-metres in diameter, and exploded with a force of 12.5 megatons of TNT, a thousand times the power of the Hiroshima atomic bomb. The resulting damage template is bigger than the Ring Road around New Delhi. But objects this small present a threat only to a limited area. Objects with diameters greater than one kilometre pose a threat to the entire globe, and can be expected to collide with the Earth with a statistical frequency of 100,000 years.

The immediate effects of a major impact, including blast, firestorms, intense acid rain, the production of pyrotoxins and the destruction of the ozone layer, coupled with the possible triggering of volcanism and seismic activity will cause a significant environmental disaster and massive loss of life and property. However, it is the vast amount of dust and debris injected into the upper atmosphere, blocking the Sun and causing phenomena similar to the nuclear winter scenario that could threaten the ecosphere on a global scale. Many smaller strikes, though not globally threatening, have caused massive damage to the area of impact, and often at considerable
distance. Two thirds of the Earth's surface is covered by water, and a major impact at sea will have far-reaching and catastrophic effects due to the production of a massive tsunami by the force of the impact. The spread of human settlement, civilisation, and particularly urbanisation, makes it much more likely that a future impact, even relatively small, could result in the massive loss of human life and property. There is currently no co-ordinated international response to this threat, and in India, there is little or no official recognition of the hazard.

Spaceguard India aims to examine the potential threat to the national and global environment posed by cometary and asteroidal impacts, measures currently in place to address the problem, and planned enhancements to the system, with a view to making recommendations concerning India's participation in the international programme at a national level.

Thanks to SpaceGuardUK for much of the content of this page.

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