Hi Brellis,<br /><br />Thanks for the post and link! Wow, fu162 was darn close in 2004! You said a 100-meter rock is needed to survive the earth's atmosphere. However, Tungkaska (sp???) blast was produced by a rock that scientists now think is only about 30 meters wide. So my guess is that 30-meters and is up is a matter of luck while anything smaller than that mostly burn up harmlessly up in the atmosphere.