Replies

http://www.nai.arc.nasa.gov/astrobio/astrobio_detail.cfm?ID=2497

Question: In the National Geographic documentary Asteroids: Deadly Impact, Dr. David Morrison states that the most likely impact scenario is ‘zero warning.’ I was wondering if this is still the case.

Answer: Yes it is, and will continue to be so for a long time. Currently we have discovered only about 3% of the small asteroids capable of doing severe damage (like the Tunguska blast of 1908). If these small asteroids are not picked up in surveys, there will be no warning. More important, however, is to take into account the risk posed by different size asteroids. The larger ones do much more damage. The NASA Spaceguard program, which has concentrated on finding the larger asteroids, has already removed more than 75% of the risk you have of dying as the result of an unexpected asteroid strike. For more information see the NASA impact hazard webpage (http://impact.arc.nasa.gov).

David Morrison
NAI Senior Scientist
11 October 2007