Before the big one hits

First, the bad news: You’ve just heard that an asteroid or a comet is about to wallop Earth and you might be in the vicinity. Now for some good news: You can find out just how severe the collision will be by logging on to

Type in your distance from the predicted impact site, as well as the size and kind of projectile, and an easy-to-use program calculates the energy of the impact and the extent of the hole it will gouge. The program also estimates the size of the fireball to be created by the impactor, when the maximum amount of heat will be given off, the strength of the shock wave that will travel through the atmosphere, and where any kicked-up debris will land.

To calculate the searing heat from the impact, the program relies on techniques from a 1977 government handbook on nuclear weapons. For seismic estimates, the program uses data from California earthquakes.

Among specifics, the program determines where and when grass will ignite, newspaper will burn, and people will suffer second- or third-degree burns. Developed by undergraduate Robert Marcus of the University of Arizona in Tucson, in collaboration with university astronomers H. Jay Melosh and Gareth Collins, the Internet site debuted on April 7.

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