Most of you probably remember the 1998 film Armageddon with Bruce Willis in the main role. A exploration team was sent to an asteroid on a collision course with the Earth. Bruce Willis of course single handedly destroyed the meteorite with a nuclear weapon preventing massive destruction to the planet.
However if it ever did crash in reality its effects would be horrendous. The impact would totally destroy the entire surrounding area for several miles. Over the course of the next few weeks dust would cover the sky preventing any sunlight from ever reaching the planet. After a few short months everything on the Earth would die since we depend on sunlight... or rather plants do.
Scientists have uncovered some very good news however. It seems that there are fewer large asteroids that could potentially destroy life on Earth than previously thought. Using an infrared sky survey rather than reflected sunlight a team of scientists at NASA picked up the heat that the asteroids emit. It depends less on the colour on the rocks which was a unpredictable method to begin with.
The survey estimated that there are 20,000 'planet busters' in the vicinity of the Earth, half previously estimated. 981 of these 20,000 have been thoroughly analysed and their mean diameter is just under 1 km, easily a 'planet buster'. This means that we are less under threat than ever before, which is quite a good future. And when considering the words of the film Armageddon : ''It happened before. It will happen again. It's just a question of when.'' The when seems to be a little bit farther away.
http://www.newscientist.com/article/mg21128332.700-fewer-big-asteroids-stalk-earth-than-we-thought.html
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