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Meteorites, and their fall to Earth, have the potential to inform studies of the asteroid impact hazard and of impact mitigation. An asteroid is a rocky object in space that’s smaller than a planet — they’re sometimes called minor planets or planetoids, according to NASA. Other sources refer to them loosely as “space debris,” or leftover fragments from the formation of the solar system. There are millions of asteroids orbiting the sun, some 750,000 of which are found in the asteroid belt, a vast ring of asteroids located between the orbits of Mars and Jupiter. Asteroids can be as large as hundreds of kilometers wide: The asteroid Ceres, sometimes referred to as a dwarf planet, is 940 km (584 miles) wide. Meteorites are usually categorized as iron or stony. As the name implies, iron meteorites are composed of about 90 percent iron; stony meteorites are made up of oxygen, iron, silicon, magnesium and other elements. The collisions of these objects with Earth are basically random events, but still we have some idea how often they happen. Localized destruction happens every couple of hundreds of years and is somewhat equivalent to a hydrogen bomb. Last such event happened in 1908 near Tunguska river in Siberia. The number of casualties depends on the place of impact (the objects of this size usually explode in the air before reaching the ground, just like an atom bomb). If a city is struck, casualties could be close to a million, while Tunguska event had zero to one reported casualty (reports vary). An impact in the ocean would create a tsunami and definitely produce significant destruction on the nearby seaside. These events usually do not leave a crater and typically involve a 100-meter asteroid or comet.

This book presents the celestial phenomena of asteroids, meteoroids and meteorites, and comets. It illustrates the role that collisions with meteors, comets, and asteroids have played in the history of Earth and other planets in the solar system and examines what is being done to protect Earth from future collisions.