Asteroid strikes are a threat, but space-based telescopes would reduce risk
The aim of Asteroid Day is to inform the public and raise awareness about the possibility that asteroids can collide with the Earth in the future. Today was chosen to highlight the risk because on the same day in 1908, a 30m object entered the atmosphere over a forested region in Siberia and exploded in mid-air. The resulting shockwave and heat levelled the forest over an area larger than greater London.
About twice a year an asteroid causes an explosion in the atmosphere that releases the energy equivalent of the Hiroshima nuclear bomb. On occasion, you can see asteroid hits first hand in the night sky when a shooting star leaves a bright streak against the starry background. A shooting star is typically only a grain-sized particle that burns up in the atmosphere, but it is the same mechanism as a larger scale asteroid collision, only with fewer consequences. Asteroids are part of our natural environment and we have lived with them as long as we have existed.
Even though there is a regular influx of cosmic material to the Earth, an asteroid impact only rarely causes damage. Usually, asteroids are too small, explode too high or enter the atmosphere over uninhabited territory such as the ocean. However, in time intervals that can be measured in tens or even hundreds of years, an asteroid impact causes significant damage.