A new website lets astronomers — and anyone who likes to watch stuff blow up — calculate the damage a comet or asteroid would cause if it hit Earth.

The interactive website, called Impact: Earth! (available at www.purdue.edu/impactearth), is scientifically accurate enough to be used by the Department of Homeland Security and NASA, but user-friendly enough for elementary school students, according to the researchers who developed it.

The site could help scientists and the public alike better understand the destructive potential of comets and asteroids, which have caused massive extinction events in our planet's past, researchers said. [Top 10 Ways to Destroy Earth.]

"There have been big impacts in the past, and we expect big impacts in the future," said Jay Melosh of Purdue University, who led the creation of Impact: Earth!. "This site gives the lowdown on what happens when such an impact occurs."

Impact events: a constant threat

More than 100 tons of material from asteroids and comets hits Earth every day, according to Melosh, who is also part of the NASA team that recently guided the Deep Impact spacecraft to within 435 miles (700 km) of Comet Hartley 2. [First close-up photos of Comet Hartley 2]

Space-rock fragments as large as a sedan hurtle into the planet a few times each year, but they usually burn up as they enter the atmosphere.

Massive impacts are rare — but incredibly powerful and destructive. When the 9-mile-wide (15 km) Chicxulub object smashed into Earth 65 million years ago, for example, it set off a cascade of events that scientists think killed off the dinosaurs and many other species.

Asteroids don't have to be as big as Chicxulub to leave a mark. Arizona's Barringer Crater — nearly a mile (1.6 km) wide — is evidence of an impact 50,000 years ago from a nickel-iron space rock estimated to be 164 feet (49.7 m) in diameter.

"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."

How the calculator works

The website allows users to enter a few parameters, such as the diameter of the impact object, its density, velocity, angle of entry and where it will hit the Earth.

The calculator then estimates the consequences of the impact, including details of the atmospheric blast wave, ground shaking, the size of any tsunami generated, fireball expansion, distribution of debris, and the size of the crater produced.

According to Impact: Earth!, if an asteroid of similar composition to the one that caused Barringer Crater — but twice as big — hit 20 miles (32 km) outside of Chicago, the impact energy would be equivalent to about 97 megatons of TNT.

The resulting crater would be almost 2 miles (3.2 km) wide, and the impact would ignite a fireball with a 1-mile (1.6-km) radius. A magnitude 6 earthquake would shake the city approximately six seconds after impact, the air blast would shatter windows and the Windy City would be coated in a fine dust of ejecta.

The site states that impacts of this size occur roughly once every 15,000 years.

Homeland security

Impact: Earth! is an updated version of an impact calculator Melosh created with some colleagues about eight years ago. The new site's graphic interface makes the site easier and more fun to use, Melosh said.

"There were a lot of requests for calculations of tsunamis that would be produced from an ocean impact, and we've added that," said Gareth Collins of Imperial College London, who worked with Melosh and others on the new version. "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."

Governmental agencies, including the Department of Homeland Security, NASA and the U.S. Geological Survey, use the site, Melosh said. The program is available in multiple languages and also is used by foreign governmental agencies.

"This calculator is a critical tool for determining the potential consequences of an impact," said John Spray, director of the planetary and space science center at the University of New Brunswick in Canada. "It is widely used by government and scientific agencies, as well as impact research groups and space enthusiasts throughout the world."

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

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

This article was reprinted with permission from SPACE.com.

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