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In July 1994 the world watched as fragments of Comet Shoemaker-Levy 9 crashed into Jupiter. This was the first time astronomers witnessed a large comet impacting with a planet. Asteroids frequently collide with earth. Many deflect off the earthís atmosphere, others burn up in the earth's atmosphere, and some of the larger asteroids have left impact craters. One of the most spectacular impact crater is a half mile wide crater near Flagstaff, Arizona. Most of earth's impact craters get erased due to the earth's ever changing surface. The impact crater off the coast of the Yucatan Peninsula, in Mexico, is thought to have caused the extinction of the dinosaurs.

Most asteroids do not cause this type of destruction. Scientists estimate that asteroids measure 330 feet would cause massive destruction. In 1908 an asteroid of this size exploded over the Tunguska forest in Siberia. The asteroid did not even hit earth and still destroyed 700 square miles of trees. It is estimated that an asteroid measuring 330 feet will hit earth on average every 100 years.

Asteroids that are 0.3 miles and larger would cause global disaster if it was to strike earth. It is estimated that asteroids of this size will strike earth only once in every 100,000 years.

The government is taking this threat very seriously. NASA has funded the upgrade of Palomar telescope at a cost of upwards of $500,000. The 48-inch Palomar telescope, near San Diego, California, will be upgraded with NASA's Near Earth Asteroid Tracking (NEAT) system.

Currently, NASA's NEAT system is mounted on a 39-inch telescope atop Mt. Haleakela on Maui, HI. The refurbished Palomar telescope will enable them to peer deeper into the space than they can from Haleakela. They will see 20 percent farther, and their field of view will be 10 times wider.

NASA's goal is to find all asteroids larger than 0.6 miles across within 10 years. It's estimated there are 1,000 to 2,000 asteroids larger than 0.6 miles that approach within 30 million miles of Earth. Less than 20 percent have been detected so far. Although the vast majority are harmless and will never pose a threat to Earth, scientists want to keep track of the tiny percentage whose orbits could eventually put them on a collision course with Earth.

If NASA ever discovers an asteroid on a collision course with earth, what next? NASA has already taken the first step in answering that question. NASA is spending $240 million on mission "Deep Impact". They will create a spacecraft that will fire 1,100 pound bullet into a cometís core. They will test this project by shooting the bullet into comet Tempel 1 on July 4, 2005. NASA is expecting the bullet to blast out a crater the size of a football field and as deep as a seven-story building. More will have to be done to protect earth from asteroid disasters.

The photograph of Palomar Observatory was taken by Bradford Behr. Palomar Observatory: Observers' Site His photograph is copyrighted. Please do not copy his photograph without his permission.


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