About one hundred tons of extraterrestrial matter strikes Earth every day, so very few meteorite strikes need to be prevented. Stopping a large comet or asteroid from striking Earth—one large enough to destroy a city, for example—may be possible with modern technology, but that would require years of research and preparation, vast sums of money, and most likely broad international cooperation. So far, such tremendous preventive efforts have not yet been made. Happily, such strikes are very rare, so there is probably still enough time to prepare for the next major strike.