The idea sounds like it has sprung straight out of the pages of a sci-fi novel: a large lump of matter in space, hurtling towards earth. But could it happen? Much of my work as a space scientist and project manager involves the assessment of risks. At a basic level, we use a very simple formula: the risk factor is defined as the potential to cause harm, multiplied by the probability of occurrence.
In the case of an asteroid strike, the probability of occurrence is small. Space is vast and, with relatively few objects out there, the chances of one hitting earth are minute. But if we look at the potential harm caused by such a collision, things don't look so good. Let's take your average, six-mile-wide asteroid -- something similar hit the Yucatán Peninsula in Mexico about 65 million years ago.
The energy released by the impact was comparable to detonating 100 million megatonnes of TNT; it destroyed everything within a radius of 250 miles and triggered global tsunamis, worldwide firestorms and huge earthquakes. It left a layer of dust in the atmosphere that many scientists believe caused the extinction of the dinosaurs. So, in our risk assessment, we have very low probability but a very high potential of harm (the end of life as we know it).
Are we doomed? Hopefully not. We are on the case: we're searching for and tracking potentially dangerous items that are out there and developing techniques to deflect any dangers away from earth.