NASA's Center for Near Earth Object Studies keeps an eye on the sky, surveying nearly 20,000 objects that pass near the Earth. The technical phrase, near Earth-objects, termed NEOs include asteroids
and comets, which are cause for concern due to their proximity and risk for collision with Earth.
As it stands now, there are roughly 2,000 potentially dangerous asteroids, of which 155 have a 1-kilometer diameter, making them 2.5 times as tall as the Empire State Building. Anyone who has dabbled in paleontology—even in the science fiction realm of Jurassic Park or The Land Before Time—knows that a giant asteroid hitting Earth is not good news for life on the planet. In fact, there is evidence that this may have been one of the main causes of the Cretaceous-Paleogene extinction.
It does not take a massive asteroid to affect widespread damage. An asteroid that was only ten meters in diameter exploded 25 km above the Bering Sea in December with the force equivalent to ten Hiroshima atomic bombs
. No international or national space organization had detected the celestial object before it disintegrated above the unsuspecting Earth.
As technology has advanced
throughout the decades, people have become better at seeing what is floating around us in the sky. According to CNEOs
, in 1900, only 28 NEOs were detected. The scale of that number did not change that drastically at the end of the century. As of 1990, only 140 NEOs and 215 potentially dangerous asteroids were detected up above. By comparison, 17,455 NEOs and 1,945 potentially dangerous asteroids were identified.