Impacts, Real and Imagined

Natural History, June, 1999 by Robert (American businessman and engineer) Anderson

Interest in earthbound comets may have peaked with Hollywood's spate of impact-related thrillers, but with the millennium approaching and a possible Leonid meteor storm predicted for November, I trust it will remain strong. The Internet is riddled with impact sites. Begin at Sandia National Laboratories' Comet Impact Simulations (sherpa.sandia.gov/planetimpact/comet), which models what would happen if a kilometer-wide comet struck the ocean. To view the results of an actual impact--a mile-wide hole in the Arizona desert--check out the Barringer Meteorite Crater (www.barringercrater.com). A 3-D game allows you to select the target city of an incoming space rock.

At Asteroid and Comet Impact Hazards (impact.arc.nasa.gov), which is maintained by NASA Ames Space Science Division, you can see what the government is doing about the threat. Don't miss the gallery, which has a movie of the Peekskill Meteorite and the car that it hit in 1993. Some idea of the complexities of waging war on incoming objects from outer space is contained in "Planetary Defense: Catastrophic Health Insurance for Planet Earth" (www.au.af.mil:80/au/ 2025/volume3/chap16/v3c16-1.htm).

Planetologist/artist William K. Hartmann has re-created an explosion that occurred in 1908 over Siberia (www.psi. edu/projects/siberia/siberia.html). Combining eyewitness accounts with recent research, he describes the damage that even a small asteroid can do. Evidence of larger collisions can be found at the Lunar and Planetary Institute's Terrestrial Impact Craters site (cass.jsc.nasa.gov/pub/ publications/slidesets/impacts.html).

Just to remind yourself that asteroids and comets are really out there, check out the Near Earth Asteroid Rendezvous page from the Johns Hopkins University Applied Physics Laboratory (near.jhuapl. edu/index.html).

Robert Anderson is a freelance science writer in Los Angeles.