Ceres, the biggest asteroid, was discovered on the first day of the nineteenth century. It is about 1000km in diameter and since 2006 has been officially promoted to the status of Dwarf Planet. Now we know over 15,000 asteroids, and in 2006,831 of them had been classed as potential hazards. This essentially means that they have orbits that bring them critically close to the Earth, and are more than 1km across. At the time of writing in 2006, the most significant asteroid hazard known was the possibility of the 320m asteroid Apophis striking the Earth on 13 April 2036. NASA and others are already working on countermeasures. This impact would cause severe damage but would not threaten mass extinction.
By contrast to the millions who have been killed by flood, earthquake and volcano, there seem to be few if any cases on record of a meteorite or asteroid killing anyone, although people have been struck by meteorites. But although asteroid impacts are rare, they are inevitably very damaging. Even a small one could cause as much destruction as a nuclear weapon, while a large one could mean mass extinction.
Perhaps the most remarkable fact about an asteroid impact is that, with a little new technology, it is the most preventable of natural disasters. It is tricky even in principle to do much about a volcano. It may become possible to predict earthquakes more reliably than we do today, and to design buildings that withstand them better, but stopping one would require godlike abilities. Likewise, complete control of the climate remains in the realm of science fiction.
By contrast, our awareness of asteroid hazards has been piqued by the fact that we can contemplate doing something about them. First, we have enough telescopes and cameras around the Earth to allow'Near Earth Objects” to be spotted more reliably than ever. One could still arrive from a clear sky, but systems now in place are diminishing the chance of such a surprise. In addition, any impact that was predicted would probably turn out to be decades in the future. So humanity would have plenty of notice.
What to do during the warning period would be a trickier choice. One idea would be to blow the asteroid to bits with nuclear weapons. However, this means people having atomic bombs, a far worse hazard to the species than any asteroid. Also, a substantial percentage of the bits of the asteroid would probably continue in much the same orbit as before and hit the Earth, with lesser but still damaging effect.
But there is no dearth of more graceful ideas. One would be to place a tiny rocket motor on the asteroid and gently nudge it into an orbit that misses the Earth. Another would be to paint one side white so that the different pressure of sunlight on its faces would shift it in its orbit, although as asteroids rotate, this might not be feasible.
While asteroid hazards to the people of Earth have not been increasing, the attention paid to them has grown rapidly. Doubtless some of the running has been made by an aerospace industry that smells profit. But if they can make money preventing our demise, why not?
Perhaps we need more creative thinking about what to do with a possible impacting asteroid. An obvious idea would be to divert it into orbit round the Earth. Even a tiny one would contain raw materials for any number of space stations or planetary probes. But perhaps it would be more fun to send it full-tilt into the near side of the Moon so we could see a new crater form before our eyes, and marvel at our cleverness in being at a safe distance as it happened.