Early Warning Systems for asteroid impacts

Asteroids and comets are small members of our solar system, some of them having orbits bringing them close to the Earth, and thus increasing the possibility of a collision. These objects are called NEOs (Near-Earth Objects). The probability of large (>1 km) NEOs impacting the Earth is relatively low but the resulting damages would be catastrophic. However, even smaller NEOs may also have disastrous consequences. On June 30th 1908, a 60 meter sized stony asteroid entered the Earth's atmosphere at Tunguska, Siberia. Due to its velocity of about 15 km/s, the NEO exploded some 9 km over ground, releasing energy equivalent to 10 megatons of TNT. The shock wave devastated an area larger than 2200 km(2), the size of a major city such as Berlin. Due to the remote location of the impact site only two men were reported killed. Such impacts are statistically expected once every 100 to 300 years, but the next large impact can only be predicted if the NEO is discovered in advance. This paper presents the current NEO detection efforts, and discusses the possibility of preventing future impact catastrophes.