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The Risk of a Comet Strike is Low - Universe Today
Although astronomers have discovered plenty of comets, they've always thought it was just a fraction (less than 3%) of the number of comets out there - and one of them might have our names on it. Fortunately, this scenario doesn't seem so likely, according to new research from scientists at the Australian National University, astronomers have probably found more like 20% of comets. That means that small comets, capable of destroying a city, probably only hit the Earth once every 40 million years, and big continent-busting comets probably only hit us once every 150 million years.