Near-Earth Asteroids of 2013: How scientists track asteroids passing close to Earth and whether we should be concerned.

by Dejamia Wouldfolk

An asteroid the size of a city flew by Earth the second week of March 2013. It was found just six days before it was set to take its course. If it was headed to directly impact our planet, would we have had enough time to react?

Due to advances in technology, scientists are discovering more and more near-Earth asteroids (NEAs). History was made last month when an asteroid flew by Earth closer than any other asteroid had come in a century–17,100 miles, as close as the orbit of most satellites. In comparison, the asteroid that passed by Earth on March 9 was  600,000 miles away, 2.5 times the distance of the moon from Earth.

If an NEA was set to directly impact Earth, would we need time to do something or would it just burn up harmlessly in Earth’s atmosphere? When car-sized asteroids hit Earth’s atmosphere, they catch fire and burn up before they reach the surface.  If an asteroid the size of a football field was to hit the Earth, it would cause significant damage. Anything from one kilometer wide or larger would potentially have worldwide effects. According to NASA Administrator Charles Bolden, praying is all anyone could do if a large asteroid was set strike Earth.

 Asteroid graph

This graph shows the relationship between the sizes of asteroids in the main belt and their quantity.  Asteroids from the main belt occasionally pass by Earth, anything larger than one kilometer would be a cause for worldwide concern.  But, as the graph above shows, as the size of asteroids increases, their quantity in the main belt decreases. (Figure from:  O’Brien, D., Greenberg, R., 2005. The Collisional and Dynamical Evolution of the Main-Belt and NEA Size Distributions. Icarus, 174, 179-212 ).


As of March 19th, the chances of being hit by a large asteroid in 2013 are 1 in 20,000. The asteroid that passed Earth in March 2013 was about the size of a city. If it had hit Earth, it would’ve destroyed a whole city according to Slooh, a robotic telescope that can be viewed through most web browsers. If an asteroid was headed for Earth now, it would take at least five years for scientists to develop a defense system to deflect it or try to destroy it, according to Bolden and John Holdren, Assistant to the President for Science and Technology.

An asteroid’s orbit is predicted by finding the elliptical path around the sun that best fits scientists’ observations of it. The object’s predicted path around the sun is adjusted until the predictions of where the asteroid should have appeared in the sky at multiple observed times match the positions where the object was actually observed to be at those same times. As more observations are used to further improve the prediction of an object’s orbit, it becomes more accurate.

Some scientists believe that asteroids coming close to Earth should be something to be concerned about. NASA is tracking about 95 percent of the largest flying objects near Earth, those that are one kilometer or larger in diameter. Could one of these untracked asteroids be headed straight for Earth? Researchers estimate that there are about 500,000 NEAs and so far, they’ve only tracked the orbit of about 9,600. On average, objects that are 50 meters or larger are estimated to hit Earth once in every 1000 years. According to Holdren, an asteroid of that size could end civilization as we currently know it. He added that only about 10 percent of an estimated 10,000 “city-killer” asteroids have been found. Considering these recent asteroids weren’t found until they were on course to pass by Earth, maybe we really should pray that there aren’t any “city-killers” headed our way.


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