The asteroid 2012 DA14 was sighted February 2012 when Granada, Spain astronomers in La Sagra Sky Survey Observatory were searching areas where asteroids had not usually been seen. Since it will be only 14,913 miles from the Earth (24000 kilometers) February 15, 2013, it will be the same height as commercial satellites. It is 164 feet (50 meters) in size. An impact with the Earth is possible, but not likely. Several asteroids have come close to the Earth in the last decade. One of the closest flybys happened on August 19, 2004 at a closest nominal distance of 0.00811 Astronomical Units. The asteroid 2012 DA14 has a predicted closest nominal distance from the Earth of 0.00018 Astronomical Units on February 15, 2013. An Astronomical Unit is the distance from the Earth to the Sun. If the asteroid is going faster than escape velocity, as expected, it will not hit the Earth.
An asteroid 131 feet (40 meters) hit a region in Tunguska, Siberia in 1908. It was near the Podkamennaya Tunguska River in Russia. It happened at 0:14 Universal Time on June 30, 1908. It damaged about 800 square miles of forest in the area. The asteroid exploded about 3 to 6 miles above the Earth. Some say it was blue in color and almost as bright as the sun. The power of the explosion is estimated to be about the same as the Castle Bravo thermonuclear test on March 1, 1954 in the United States and one-third the power as the largest nuclear weapon ever detonated Tsar Bomba. It is estimated the ground shook at the impact of the asteroid at the strength of an earthquake of about 5.0 on the Richter scale. An earthquake this size is only moderate and does not damage well-constructed buildings.
One of the most famous asteroids that came close to the Earth is the minor planet Icarus. It is 1.4 kilometers in size. It was discovered in 1949 by Walter Baade and first named asteroid 1566. It is called Icarus after the story in Greek mythology of the boy who flew too close to the Sun. It is an Apollo asteroid. It will come close to the Earth on June 16, 2015 just like asteroid 2012 DA14, although its predicted nominal distance will be 5 million miles, which is much farther than the predicted nominal distance of 14,913 miles for asteroid 2012 DA14.
The Barringer Crater in Arizona is one of the first recorded impacts of meteors and comets. It happened about 50,000 years ago
during the Pleistocene epoch. It was named after Daniel Barringer who was one of the first to correctly consider the crater was caused by a meteorite. It was caused by a nickel-iron meteorite about 50 meters across. The crater itself is 0.737 miles in diameter. Other craters include Rio Cuarto in Argentina (10,000 years ago), and Henbury Craters in Australia (2,500 years ago). Eugene Shoemaker devised a theory of how often an impact can occur. He theorized that an impact that is as powerful as an atomic bomb happens once a year. The reason it is not noticed is the impact usually happens in the ocean because about 75% of the Earth is ocean. Exceptions are the Sikhote-Alin meteorite in Siberia, Russia in 1947 and the Revelstoke fireball in 1964 in the snows of British Columbia, Canada.
Some plans are being made to destroy the asteroid if it comes close enough to the Earth for a probable impact next year. One idea is to build a rocket ship that can paint the asteroid so it cannot reflect sunlight. This would alter its spin and change its temperature. According to Aleksandr Devaytkin, head of the observatory in Pulkovo, this could, however, make a collision in its next close approach in 2056 even more dangerous. The rocket ship could also blast the asteroid into the Pacific Ocean or Atlantic Ocean, but they do not think they have enough time to build the rocket ship. The International Space Station or retired Space Shuttles Endeavour, Atlantis, and Discover are possibilities. The ISS will definitely be used for the exact location of the asteroid in February, 2013.