A Web-Based Asteroid Impact Simulator

By Roland Piquepaille

Ready to have some fun while learning some physics? Try the new Earth Impact Effects simulator. This news release from the University of Arizona (UA) tells us more about this simulator of a collision between an asteroid and the Earth. You enter several parameters, such as the speed, the size or the density of the asteroid. And bingo! The program tells you the crater size or the seismic magnitude of the impact. As UA says, if dinosaurs have had this program 65 million years ago, they would have known that the Chicxulub impact generated a seismic shaking of magnitude 10.2 on the Richter scale.

Next time an asteroid or comet is on a collision course with Earth you can go to a web site to find out if you have time to finish lunch or need to jump in the car and DRIVE.

University of Arizona scientists are launching an easy-to-use, web-based program that tells you how the collision will affect your spot on the globe by calculating several environmental consequences of its impact.

You type in your distance from the predicted impact site, the size and type of projectile (e.g. ice, rock, or iron) and other information. Then the Earth Impact Effects Program calculates impact energies and crater size. It next summarizes thermal radiation, seismic shaking, ejecta deposition (where all that flying stuff will land), and air-blast effects in language that non-scientists understand.

Included with the results are descriptions of the algorithms and references to scientific sources.

Basically, the program is based around four environmental effects.

• Thermal radiation. An expanding fireball of searing vapor occurs at impact. The program calculates how this fireball will expand, when maximum radiation will occur, and how much of the fireball will be seen above the horizon.
  
• Seismic shaking. The impact generates seismic waves that travel far from the impact site. The program uses California earthquake data and computes a Richter scale magnitude for the impact. Accompanying text describes shaking intensity at the specified distance from the impact site using a modified Mercalli scale This is a set of 12 descriptions ranging from "general destruction" to "only mildly felt."
  
• Ejecta deposition. The team used a complicated ballistics travel-time equation to calculate when and where debris blown out of the impact crater would rain back down on Earth. Then they used data gathered from experimental explosions and measurements of craters on the moon to calculate how deep the ejecta blanket would be at and beyond the impact-crater rim.
  
• Air blast. Impacts also produce a shock wave in the atmosphere that, by definition, moves faster than the speed of sound. The shock wave creates intense air pressure and severe winds, but decays to the speed of sound while it's still close to the fireball, Melosh noted. "We translate that decreasing pressure in terms of decibels