November 4, 2010

Updated Asteroid ‘Impact Calculator’ Unveiled

Scientists at Purdue University and Imperial College London have revised their popular "ËœImpact Effects Calculator', which allows anyone to calculate the potential damage a comet or asteroid would cause if it collided with the Earth.

The interactive tool, available at, lets users enter in specific details about the hypothetical impactor, such as its diameter and density, velocity, angle of entry and where it will hit the Earth. It then estimates the scale of the ensuing catastrophe, including details about the size of the crater left behind, ground shaking, size of the tsunami generated, distribution of debris, and even how far away a person would need to be to avoid being buried or set ablaze in the blast.

"Comets and asteroids have become a part of our popular culture, but we don't really know a lot about their composition and internal processes as they fly through space," said Jay Melosh, a distinguished professor of earth and atmospheric sciences and physics at Purdue University, who led the creation of the program.

"We have much more to learn about these objects that are often our closest neighbors in space. We do know that sometimes they enter into a collision course with the Earth, and this site offers an authoritative place to go to learn about the detailed effects of an impact," Melosh said in a statement on the Purdue web site.

The impact effects calculator is scientifically accurate enough to be used by homeland security and NASA, but user-friendly and visual enough for elementary school students, said Melosh, an expert in impact cratering.

"The site is intended for a broad global audience because an impact is an inevitable aspect of life on this planet and literally everyone on Earth should be interested."

"There have been big impacts in the past, and we expect big impacts in the future. This site gives the lowdown on what happens when such an impact occurs," he said, adding that 100 tons of material from asteroids and comets strike the Earth every day.

In fact, even fragments as large as a car hurtle toward the planet a few times each year, although these burn up as they enter the atmosphere.

"Fairly large events happen about once a century," Melosh said.

"The biggest threat in our near future is the asteroid Apophis, which has a small chance of striking the Earth in 2036. It is about one-third of a mile in diameter, and the calculator will tell what will happen if it should fall in your backyard."

While massive asteroids like the 9-mile-wide Chicxulub that wiped out the dinosaurs 65 million years ago are very rare, smaller and more common asteroids have left craters that remain today.  For example, Arizona's Barringer Crater, which is nearly a mile wide, provides evidence of an impact 50,000 years ago from an asteroid estimated to be 164 feet in diameter and composed of nickel and iron.

According to the Impact Earth calculator, if an asteroid of similar composition but twice as large struck 20 miles outside of Chicago, the energy would be equivalent to about 97 megatons of TNT.  The resulting crater would be almost two miles wide, and would ignite a fireball with a one-mile radius, producing a magnitude 6 earthquake that would shake the city approximately six seconds after impact.  The air blast would shatter windows, leaving the entire city coated in a fine dust of ejecta.

The new, revised tool is a more visual and user-friendly update to an impact calculator Melosh created with Robert Marcus and Gareth Collins about eight years ago while at the University of Arizona.

Melosh said he and Collins collaborated with Information Technology at Purdue (ITaP) to update the program and create a graphic interface to make the site easier and more fun to use.

"There were a lot of requests for calculations of tsunamis that would be produced from an ocean impact, and we've added that," said Collins, a natural environment research council fellow at Imperial College London.

"In addition, the program now visually illustrates the information the user enters, and we plan to connect the program with Google Earth to show a map of the effects."

Worldwide, the web site received more than 10 million hits from around the world in the week following the launch of the first impacts effects calculator.

Today, governmental agencies such as the Department of Homeland Security, NASA, the U.S. Geological Survey and the U.S. Air Force link to and use the site, which is available in multiple languages, Melosh said.

Foreign governmental agencies also use the site, he said.

"It is a valuable tool to quantify the important impact processes that might affect the people, buildings and landscape in the vicinity of an impact event," said Melosh.

"With the program we include a scientific paper that describes the approximations and equations and discusses the uncertainty in our predictions. One can delve as much into the science as they would like."

The calculator also has been a valuable tool in sparking young students' interest in science, Melosh said.

"The calculator has been used by teachers and students from kindergarten through high school both for school projects and for fun."

"At one point we debated whether or not to use scientific notation in the results, but a teacher asked us to keep it. She told us that it inspired her class and the students worked hard to learn the method so they could fully understand the results."


Image Caption: "Impact: Earth!" (Information Technology at Purdue image/Michele Rund). Download full poster.


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