Solar system includes millions of small bodies of
§Solar system includes millions of small bodies of matter §Range in size from bits of dust and floating ice to small moons
§ Largest of the small bodies are asteroids, minor planets § Fragments of rock that orbit the sun § More than 50, 00 § Largest known, Ceres, about 1, 000 km in diameter § Most exist in region between Mars and Jupiter, called asteroid belt
§ Classified in 3 types based on composition § 1) composed entirely mostly of carbon materials; have dark appearance § 2) composed mostly of iron and nickel; have a metallic appearance § 3) Most common, made of mostly of silicate materials; look like earth rocks § Thought that asteroids in asteroid belt are remains of planetesimals that weren’t able to from planets § Composition of asteroids is very similar to planets
Comets § Comets are bodies of rock, dust, methane, ammonia, and ice § Orbit sun in long ellipse § Core is rock, metals and ice § Spherical cloud of gas and dust, coma, surrounds the core § Together core and coma makeup head of comet § Tail of comet is gas and dust that streams from head; always points away from sun § Thought that most comets form in Oort cloud, a spherical cloud of dust and ice that contains cores of trillions of comets § Cloud surrounds solar system § Orbits sun at a rate of 140 m/sec (millions of years per revolution) § Gravity of nearby star may force comet out of cloud and into orbit around sun
§ Long—period comet- periods of several thousand of million years § Short-period comet- periods of up to 100 years § Haley’s comet- every 76 years; last appeared in 1986
§ Meteoroids are small bits of rock or metal § Most are less than one mm in diameter (pieces of comets) § Some are more than 1 cm in diameter § Meteoroids that enter earth’s atmosphere are called meteors § Most burn up in atmosphere before reaching earth’s surface; produces bright streak of light § Called shooting stars § Can vaporize very quickly in bright flash of light; called fireball § Sometimes large numbers of meteors can enter earth’s atmosphere in a short period of time; called meteor shower § Occur at same time each year; earth intersects orbits of comets left behind
§ Not all meteors burn up in atmosphere § Meteors or any parts left after hits earth’ surface is called a meteorite § Small with masses less than 1 kg § Occasionally large meteorites struck with force of a bomb § Meteorites classified into three types: § 1) Stony meteorites- similar in composition to rocks on earth § 2) Iron meteorites- have distinctive metal appearance § 3) Stony-iron meteorites- contain both iron and stone
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