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COMETS COMETS • A comet is a small body of ice, rock, and cosmic dust loosely packed together • Comets contain a nucleus, dust tail and an ion tail COMETS • Referred to as DIRTY SNOWBALLS due to their composition • Probably left over from the time when the planets formed COMETS COMETS • Passes close to the sun, solar radiation heats the comet and gas and dust stream off in the form of a LONG TAIL • TWO TYPES OF TAILS • dust tail and an ion tail • Center is the nucleus COMETS • Elongated orbits • Ion tail always POINTS AWAY from the sun – ion tail is blown away by solar wind (made of ions) • Dust tails don’t always point away from the sun COMETS • Scientists think that comets come from: • Oort Cloud, spherical region that surrounds the solar system • When gravity of a passing planet/star disturbs part of the cloud, comets can be pulled toward the sun. • Kuiper belt, which is the region outside the orbit of Neptune. ASTEROIDS ASTEROIDS • Small, rocky bodies that revolve around the sun • Irregular shapes • Orbit in the ASTEROID BELT – wide region between the orbits of Mars and Jupiter • Thought to be material left over from the formation of the solar system Asteroid Belt Types of Asteroids • Outermost region of asteroid belt asteroids are dark reddish brown (may be rich in organic material) • Asteroids – dark gray surfaces – rich in carbon • Inner most region – asteroids are light gray (stony or metallic composition) • Examples: Hektor, Ceres, Vesta Examples of Asteroids METEOROIDS • Meteoroid - A small, rocky body that revolves around the sun – probably pieces of asteroids • Meteorite – meteoroid that enters earth’s atmosphere and strikes the ground • Meteor – bright streak of light caused by a meteoroid/comet dust burning up in the atmosphere Meteor Meteors • Meteor Showerhappen when Earth passes through the dusty debris that comets leave behind Types of Meteorites IMPACT CRATERS IMPACT CRATERS • When an object in space collides with another object in space – impact crater • Planets/moons with no atmospheres have MORE IMPACT CRATERS • Atmosphere acts as a shield – smaller objects “burn up” Impact Craters • Every few thousand years impacts may be powerful enough to cause a natural disaster • Impact that is large enough to cause a global catastrophe are estimated to happen once every few hundred thousand years, on average TORINO SCALE • System that allows scientists to rate the hazard level of an object moving toward Earth • 0 = small chance of hitting Earth • 10 = definitely will hit Earth