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it is possible to detect objects even just a few meters in diameter, but those are purely chance discoveries. and even then they have to pass very near the earth to become bright enough to detect. the problem is, there is just no way to detect all the objects larger than say 10 meters (these can survive the fall through our atmosphere and explode near the surface, causing megaton size explosions), as these objects probably number in the billions or more!
the best we can hope for is to someday be able to track all objects larger than say 100 meters, those have the potential to devastate entire countries. even this task is currently well above the capabilities of the rather limited network of telescopes searching for earth crossing objects at the moment.
what IS currently being worked on is finding and tracking the 'global killers', objects about 1 km in size or larger, those can put us back into the stone age (those few people that actually survive the first year after impact). iirc it will take a couple of decades to achieve this at the current rate of discovery.
the second issue is, of course, what to do if we actually find an object on collision course. blowing it up is not a good option, as that only leaves many smaller fragments that are still going to hit, possibly doing even more damage than the single larger impact! the only real option is deflection and the only feasible way to achieve this with the current technology are nuclear weapons, detonated above the surface of the asteroid. problem is, we have neither warheads powerful enough (or maybe we do, not really sure about the power of the weapon required) nor a delivery system that could reach the target.
so basicly, if anything is intent on hitting us in the next decade or so, there's nothing we can do about it. fortunately, the chances of that happening are rather miniscule.
[ 09-03-2003, 06:18 PM: Message edited by: frudi_x ]
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