Death by Asteroids!

Many doomsayers predict that life on Earth will be destroyed by an asteroid, maybe as soon as the end of the year! How likely is that to happen? Everyday Einstein surveys the damage.

Lee Falin, PhD,
November 9, 2013
Episode #020

Death by Asteroids!A popular prediction among doomsayers is that an asteroid will strike the earth in the near future, completely destroying life as we know it. We've all seen it in movies multiple times, so there's obviously a good chance that it will happen in real life, right?

That's No Moon

The thing is, asteroids are hitting the Earth all the time. Fortunately the Earth's atmosphere protects us from most smaller asteroids. In fact, According to NASA, only asteroids that are larger than the size of your average office building actually pose any threat to us. Asteroids that are larger than the average office building but still under 1 km in size, can do significant damage on the local scale.

The only object that large to have hit the Earth in recorded history was the Tunguska meteoroid in 1908, (though most scientists believe it exploded in the air above Tunguska, rather than actually hitting the ground). The damage caused by this explosion was constrained to an isolated region of Siberia, which is fortunate as the force of the explosion destroyed the vegetation within 9 miles of impact, and knocked over trees as far away as 25 miles.

An interesting thing about the "Tunguska Event," as it is known, is that nobody actually saw it up close. In addition, many of the early studies of the event by Russia have been lost over the years. This lack of direct information has led to some interesting hypotheses about just what caused this event. Everything from dark matter to aliens has been suggested, though most scientists agree that the most likely culprit was a meteoroid fragment around 100 meters in diameter.

The Big One

If a very large asteroid, (anything larger than 2 km or 1.2 miles in diameter) were to hit the earth, the results would be catastrophic. Aside from the immediate damage surrounding the impact itself, scientists believe that such an impact would cause global environmental changes. These changes would result in the loss of crops, causing widespread starvation and disease. Most scientists also agree that it was a very large asteroid impact that caused the mass-extinction of the dinosaurs. (Though they can't quite agree on the exact size and nature of that event).

The Sky is Falling

So how likely is such an event to occur? Are there monster-sized asteroids hurtling towards Earth right this minute? Should you quit your job now and start building your underground shelter? Fortunately there are several teams around the world that spend a considerable amount of time searching for "Near Earth Objects" or NEOs, which might pose a threat to life as we know it.

At the time of this writing, the object of most significant risk of hitting the Earth is the "2011 AG5" asteroid. According to NASA, AG5 is expected to pass within .3 radii of Earth in 2040.

While the AG5 is relatively small, only 140 meters in diameter, this is still large enough to cause considerable local damage. These facts give the event a rating of 1 on the Torino Scale, the rating system NASA uses to gauge the danger of asteroid impacts. A score of 0 on the scale means no danger whatsoever, while a score of 10 means we're all going to die.

According to the latest reports from NASA, there is currently a 99.8% chance that this asteroid will miss us completely. Just how unlikely is that? Well 99.8% is equivalent to a 1 in 500 chance. That means that if you were in charge of the fate of the universe, and wanted to leave it all up to chance, you could put 499 white marbles in a bag along with one red marble. Then shake the bag up and pull out a marble. If it’s red…boom!

See also: What is Probability?

Like all models, this one has a bit of uncertainty. NASA won’t be able to refine their projections until 2023, when they can get a better idea of how Earth's gravity will affect the course of the asteroid.

If that happens, NASA is prepared to carry out "one of several viable missions to change the asteroid's course." (This probably means calling a team led by Bruce Willis). Given the relatively small degree by which the asteroid is projected to miss the Earth, and what we know about the uncertainty of model projections, you might not want to rule out that underground bunker just yet.


If you're interested in tracking Near Earth Objects yourself, you can find the complete list, along with their risk assessments, on NASA's Near Earth Object page. While most of the names of these objects sound rather sedate, one that stands out as particularly ominous is "99942 Apophis" which someone decided to name after the Egyptian demon who tried to kill Ra by swallowing the sun. (Disclaimer: Everything I know about Egyptian mythology I learned from reading Rick Riordan).

Do you have your own tips for surviving asteroid collision? If so, please share them in the comments below.

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Asteroid in space and Small Asteroids images from Shutterstock

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