NEO is an acronym is for near earth object. This means that there are objects orbiting the earth at a distance that can be classified as being in close proximity to earth. When these objects are close to earth there is always a chance that there may be a collision between these objects and earth. There have been several near misses throughout history where an object such as a comet or an asteroid came very close to colliding with earth and causing a huge amount of damage to earth and the atmosphere.
On March 18, 2004 an asteroid was recorded as being extremely close to earth and there was a high potential that it might actually hit earth. An asteroid with a diameter of thirty meters or one hundred feet passed approximately forty thousand kilometres above the earth’s surface. While this does not sound like it was in close proximity to earth it was in actuality half the distance between the earth and the moon. It was considered a serious threat to earth because it was not detected until three days before it was suspected that it would hit earth.
Again on March 31, 2004, another NEO was noticed orbiting around earth. This time the near earth object was only sixty-five hundred kilometres away from earth. However there was not a considerable amount of danger associated with this NEO because it is was relatively small in size. Its diameter was measured to be about six meters. It was detected only hours before its closest approach. It was expected that had this NEO actually hit earth that it would not have caused any serious damage and it would have likely dissolved in the atmosphere.
All NEOs that are within a certain distance from earth are now recorded and catalogued. When a NEO is witnessed in space, it is then ranked on a scale to determine the potential danger that it may pose to earth and what kind of damage it may cause if it was to collide with earth. The real danger here is that some NEOs do not get witnessed until a few days before they could possibly collide with earth.