THE sight of the solar system鈥檚 biggest planet being battered by the broken remains of a comet in 1994 left a vivid reminder of our own planet鈥檚 vulnerability. The scars that remained after the series of giant impacts on Jupiter were more prominent even than its great red spot, and remained visible for months.
This dramatic spectacle was enough to loosen government purse strings, and the funding has supported telescope surveys to hunt down asteroids that could wallop us. A decade and a half after comet Shoemaker-Levy 9 smashed into Jupiter, those surveys have catalogued more than 80 per cent of the near-Earth asteroids larger than 1 kilometre across.
Now we have seen the results of the first exercise ever to test plans for what to do if an asteroid is on collision course with Earth (see Asteroid attack: Putting Earth鈥檚 defences to the test), and they do not inspire confidence. We still have a long way to go before we can say we are prepared for this cosmic threat.
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Improved early-warning capabilities are one cost-effective solution. There are telescopes on the drawing board that could find objects as small as 140 metres in diameter. That鈥檚 a big advance on what we can do now, even if objects 30 to 50 metres across are more numerous and therefore arguably more dangerous.
鈥淭here are telescopes on the drawing board that could find objects as small as 140 metres in diameter鈥�
More in-depth exercises are needed too, to hone our plans for communication and coordination should a city find itself in the target zone of an incoming asteroid.
Better still, of course, would be having the capability to fend off dangerous asteroids. It has long been recognised that the quick and dirty way to do this is to explode a nuclear bomb nearby to blast the asteroid off-course. That means we should revisit the international treaties that prohibit the launching of nukes into space, and try to come up with carefully drafted wording to allow their use if an asteroid threatens.
Whatever action is taken needs to be proportionate to the risk. The compared to the risk of routine insults from hurricanes, earthquakes and other natural disasters of entirely terrestrial origin. Last year such events .
Resources are finite, and any plans to construct cosmic defences need to be measured against down-to-earth goals. When assessing the case for a better census of dangerous asteroids and their orbits, for example, let鈥檚 not forget that this could also help us understand how our solar system came to be.
As far as preparing for doomsday, it鈥檚 the terrestrial threats that should be at the front of planners鈥� minds. Blueprints for evacuation and medical help to meet these threats will serve us equally well if a city is ever unlucky enough to get pummelled by an impactor.
