Near-Earth Object
A Near-Earth Object (NEO) is a comet or asteroid that has been allegedly nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood. Composed mostly of water ice with embedded dust particles, comets originally formed in the cold outer planetary system while most of the rocky asteroids formed in the warmer inner solar system between the orbits of Mars and Jupiter.
NASA actually has a Near-Earth Object Program "to coordinate NASA-sponsored efforts to detect, track and characterize potentially hazardous asteroids and comets that could approach the Earth. The NEO Program will focus on the goal of locating at least 90 percent of the estimated 1,000 asteroids and comets that approach the Earth and are larger than 1 kilometer (about 2/3-mile) in diameter, by the end of the next decade. In addition to managing the detection and cataloging of Near-Earth objects, the NEO Program office will be responsible for facilitating communications between the astronomical community and the public should any potentially hazardous objects be discovered."[1]
NASA claims that "[a]s of May 26, 2007, 4708 Near-Earth objects have been discovered. 713 of these NEOs are asteroids with a diameter of approximately 1 kilometer or larger. Also, 855 of these NEOs have been classified as Potentially Hazardous Asteroids (PHAs)."[2]
