Asteroid Deflection

Asteroid Deflection

The Asteroid Deflection Research Center will develop ways to neutralize threatening asteroids.


Practicing asteroid deflection. I'm Bob Hirshon and this is Science Update.

On any given day, the odds of a large asteroid hitting the Earth are, well, astronomically low. But if it happened, it could wipe out an entire city, or worse. That's why Iowa State University has created an Asteroid Deflection Research Center, led by aerospace engineer Bong Wie.


We are not going to propose some science-fictional scheme. We will be very realistic in selecting many options already available to us.

Possible strategies include blowing up the asteroid in space with a nuclear weapon, smacking it with a projectile, or using a spacecraft's gravity to slowly drag it off course. Wie will be working with scientists around the world; they'll not only model these approaches on computers, but also practice on small, non-threatening asteroids in space. I'm Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

You probably haven't been up nights worrying about an asteroid hitting the earth, but that's okay. A handful of scientists like Dr. Wie are doing the job for you—and they actually might be able to do something to prevent it.

Although there are no known asteroids on a collision course with earth right now, in the (very) long run, it's only a matter of time before one hits. It's happened many times in the past. The most famous impact happened about 65 million years ago, when an asteroid 6 to 10 kilometers in diameter slammed into Mexico's Yucatan Peninsula, setting off an explosion equivalent to 100 trillion tons of TNT—over 6 billion times as powerful as the nuclear bomb that leveled Hiroshima at the end of World War II. Among other things, the impact incinerated everything within hundreds of miles, set off gigantic tidal waves, earthquakes, and volcanic eruptions, and ejected dust and debris into the sky that blocked the sun for years. The majority of species on earth at the time, including the dinosaurs, were killed off by this catastrophic event. Luckily, humans weren't around yet.

However, the human race dodged a bullet in the form of another impact just a century ago. On June 30, 1908, a massive explosion in the sky obliterated some 80 million trees in the remote forests of Siberia, Russia. Scientists believe the explosion was a meteor or comet, much smaller than the asteroid that killed the dinosaurs, which burned up several miles above the earth's surface. Because the earth rotates, had the object struck about five hours later, it may have completely destroyed St. Petersburg, Russia's capital at the time.

Since then, scientists have learned that meteors and comets burn up in the atmosphere surprisingly often, but most of the time the fireworks are too small and distant to notice. Recent estimates suggest that the object that exploded over Siberia may have been as little as 40 meters (131 feet) in diameter, and that objects that size may strike the earth, on average, once every few hundred years. In the past, similar impacts may have gone unnoticed because they happened over the oceans or unpopulated areas. However, just one impact on a populated area could be devastating, and the spread of the human population across the earth's land mass grows with each passing year.

As you heard, there are several possible strategies for deflecting an asteroid. One is to blow it up in space with a nuclear weapon. This may be the most effective approach, since it could completely vaporize the asteroid—but it might merely shatter the asteroid into hundreds or thousands of fragments, some of which could still be large enough to cause damage. Another possible strategy is to strike the asteroid with an object like an unmanned satellite, and knock it off course like a billiard ball. Finally, a large, heavy spacecraft could be sent to use its own gravitational pull to tow the asteroid slowly out of earth's path. This strategy would require a long time to execute, but it could potentially work on clusters of space rubble that couldn't be deflected by other means.

Of course, nobody wants to test these ideas for the first time on a potential doomsday asteroid. Computer models provide the easiest means to test hypotheses, but practical experiments are in the works as well: the European Space Agency, for example, is preparing an experimental asteroid deflector mission called Don Quijote. The mission will involve two spacecraft: one to fly up to an asteroid and assess its mass, shape, and gravity field, and another to strike the rock at just the right place and time to set it off course.

Now try and answer these questions:

  1. What are possible consequences of an asteroid impact?
  2. What are some possible strategies for asteroid deflection? What are their pros and cons?
  3. What challenges do scientists face in trying to prepare for something this rare and large-scale?

You may want to check out the July 11, 2008, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: news from space (deflecting asteroids, catching a supernova in the act, capturing the sun in 3-D, and new names for old planets).

Going Further

For Educators

Read more about the Don Quijote mission on the official European Space Agency site.

The National Geographic News article Are Asteroids History's Greatest Killers? links mass extinctions to asteroid impacts throughout Earth's history, while Undetectable Asteroids Could Destroy Cities describes a potential future risk from small, less obvious asteroids.

The National Geographic Interactive feature Asteroids: Deadly Impact explores asteroids, meteors, and their impact on Earth.

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