Today, Earth is going to have a close call with an asteroid the size of an aircraft carrier. While the asteroid, 2005 YU55, will pose no threat to Earth, the fact that such a huge space rock will be coming within the Moon's orbit serves as stark reminder that we live in a cosmic shooting gallery of sorts, populated by millions upon millions of miniscule worlds, some of which are big enough to do great harm here on Earth should they hit out planet.
As of now, there are millions of asteroids floating around the solar system, mostly in the Main Asteroid Belt, which is safely between the orbits of Mars and Jupiter. Of the millions of asteroids over 7,000 are classified as near-Earth. Of the near-Earth objects, over 1,000 are considered as "potentially hazardous," which is defined as an object over 500 feet in diameter that can come within 4.6 million miles of Earth. Obviously, a metallic space rock 500 feet across traveling at up to 15 miles per second could do an immense amount of damage. For comparison, the object (most likely a comet) that caused the Tunguska Incident was probably less than 100 yards (300 feet across, or only about a quarter the diameter of 2005 YU55) but still leveled forests for over 1,000 square miles.
Needless to say, if such an object (even a small one) were to hit a populated area, the death toll would be apocalyptic. Large impactor? Worldwide devastation and possibly an end to civilization as we know it, all the more reason to keep looking and work on planet defense systems.
Unfortunately, the truth is that the world would probably be helpless to do anything as of right now if a doomsday asteroid were to be discovered. When doomsday scenarios are considered, planners usually give months or even years advance notice time to come up with a plan to divert the colliding body and save the world. However, new asteroids are being discovered all the time, often within just days or even hours of close passage to the Earth.
So, if scientists were to discover a doomsday asteroid on a collision course with Earth, would there be enough time to do anything about it or would we simply have to resign ourselves to a terrible fate and possibly go down in history like the dinosaurs?
It's a not a pleasant thought, but one that may just come true. All the more reason to keep scanning the skies and breath a collective sigh of relief when a big space rock like 2005 YU55 passes harmlessly, albeit a bit too close for comfort, by our planet..
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