Due to the theories and studies by scientists about the stars and the Earth, the theory of a celestial impact (http://en.wikipedia.org/wiki/Impact_event) is something that is also widely studied. While this theory seems a little far-fetched, it may not be. Some astronomers study the asteroid belt and the asteroids that inhabit our solar system and are on longer, elliptical orbits throughout the system, some coming dangerously close to the Earth. The study of the Earth’s crust has proved that several meteorites have hit the Earth, some big enough to cause catastrophic damages to both the ecosystem and to the planet itself.
One such asteroid that scientists study is the Cretaceous-Tertiary Asteroid, which is supposedly the asteroid that slammed into the Earth, killing all the dinosaurs and most of the living plant life on a global scale (http://en.wikipedia.org/wiki/Cretaceous-Tertiary_extinction_event). This ties into the end of the world theories in that if an asteroid of this size were to strike the Earth during this age, it could have a devastating effect on every living thing on the planet. Not only would the entire human race be wiped out, so would the animals, sea life, and plant life. Some astronomers state that the asteroid that would cause such an event would not even need to be very large, anywhere from .6 miles across to 6 miles in diameter. While this does not seem like it would be large enough to create a global extinction, the impact of something that size would be enough to cause a blackout of the sun for many, many years that would kill off the entire planet.
Most asteroids are smaller than the size of a car, and the majority of them burn up when they enter the atmosphere, causing no real threat to humanity or to any of the life on Earth. The larger asteroids that come into contact with planets are around one half of a mile in diameter, and only come near the Earth once every half a million years. The bigger the asteroid, the more improbable the calculations are that the asteroid would actually come into contact with the gravity or the atmosphere of the Earth itself. The asteroids that are on this larger scale, or even bigger than that, are constantly monitored by space programs and astronomers all over the world.
Although there are some astronomers who believe that they can see patterns in the number of the meteorites that are hitting, or coming near, the Earth, there is no end of the world theory that is based on this, as of yet. These scientists have created a theory that states that when a certain star, named the Nemesis Star, passes through the Oort cloud of meteorites on it’s orbit around the galaxy, it causes meteorites to rain down upon the Earth.
But, there is one star that is on an elliptical orbit around the galaxy that could cause this kind of a theory to come true. The star that is known as Gliese 710 does orbit around the Milky Way, and according to some projections, will be within a little over a light year from our own sun in around 1.5 million years (http://en.wikipedia.org/wiki/Gliese_710). This would cause a massive amount of asteroids and comets from the Oort cloud to hit the Earth and all the planets of the solar system. Yet, even with this probability, the chances of this happening are only around 5%.
Although some might dismiss the possibility of a celestial impact with the Earth, there have been several “near misses” in recent years. Some of these include: an approximately 300-500 meter asteroid that passed under 500,000 miles of Earth on May 19, 1996 and was only detected a couple of days before, not allowing the time for any type of preperations if the asteroid were to have hit the Earth; a smaller, 30 meter asteroid passed within 40,000 kilometers of Earth on March 18, 2004, only after it was detected, and even though this small of an asteroid would have burned in the atmosphere, it was still a very close call; and the closest call that the Earth has had to date (since the beginning of astronomy and the study of the asteroids that approach the Earth) was when a very small meteroid passed within less than 7,000 kilometers of the Earth, and even though this tiny asteroid was classified as a meteroid, it was still a significantly close call.
Since astronomers have begun studying the asteroids that are large enough to do damage if they were to hit the Earth, there have also been many predictions that have come out due to some of the findings. While most of the asteroids that will come close enough to enter our atmosphere are small enough that they will burn up upon entry, there have been some discovered that are large enough to do the type of damage that was done in the era of the dinosaurs.
For example, there is a 1 in 17 chance that a 320 meter asteroid will impact the Earth on April 13, 2029. This asteroid was discovered by NASA in 2004 and although their projections have concluded that the asteroid will only come within a little over 25,000 kilometers of the Earth (still within the orbits of our communications satellites), it will most likely not hit the Earth. But, the prediction still stands that this close of a pass to the Earth will alter the course of this asteroid, and it could still hit the Earth on April 13 or 14, 2035 or some time later in the 21st Century.
There is also yet another major asteroid that is closer to 580 meters that will have a high probability of hitting the Earth in early May of 2102, and scientists are studying this asteroid to see if their projections will be correct or if the asteroid has a chance of turning and heading another direction or missing the Earth.