Asteroid impact expert says detection more important than deflection; inaugural ‘Asteroid Day’ Tuesday (June 30)

June 29, 2015  

WEST LAFAYETTE, Ind. - A Purdue University asteroid impact expert says the best investment in asteroid defense is not in weapons to deflect them, but in telescopes and surveys to find them.

Asteroid Day will be held on Tuesday (June 30), the anniversary of the 1908 Tunguska event, in which a large asteroid hit Earth. The day is part of a global awareness campaign to learn about asteroids and what can be done to protect the Earth from asteroid impacts, according to the asteroid day website.

H. Jay Melosh, Distinguished Professor of Earth, Atmospheric and Planetary Sciences and Physics, is an expert in impact cratering and a co-creator of "Impact: Earth!" a tool to estimate the potential damage a comet or asteroid would cause if it hit Earth.

Melosh co-authored the 2010 National Research Council report "Defending Planet Earth" that explored the feasibility of detecting all Earth-crossing asteroids greater than 140 meters in diameter and ways to mitigate their hazard.

"The good news is that more than 90 percent of the large, civilization-ending asteroids that cross the Earth’s orbit have been found, and none is threatening us,” Melosh said. “Smaller asteroids, which are less devastating, but more numerous, are our biggest concern, but with early detection we could evacuate areas threatened by such strikes. Investments in telescopes that can find asteroids in our current blind spot, the side of the Earth facing the sun, would be helpful, as would programs to find and track smaller asteroids.”

“Impact: Earth!” has been used by homeland security and NASA, but it is user-friendly and visual enough for elementary school students, he said.

Users of “Impact: Earth!” first 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 site then estimates the consequences of its impact, including the atmospheric blast wave, ground shaking, size of tsunami generated, fireball expansion, distribution of debris and size of the crater produced.

In addition to his expertise in the effects of asteroid impacts, Melosh has been involved in asteroid deflection research for years. He was a co-investigator on NASA's 2005 Deep Impact mission, which successfully targeted and hit a comet with a spacecraft. He also developed an approach to deflect an asteroid through the evaporative effects of focused sunlight. A paper detailing this work was published in the Nov. 4, 1993, issue of Nature. 

Writer: Elizabeth K. Gardner, 765-494-2081,

Source: H. Jay Melosh, 765-494-3290,

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