 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 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 140m/sec (millions of years per revolution)  Gravity of nearby star may force comet out of cloud and into orbit around sun Comets

 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 1cm 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