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Minor Members of the Solar System 23.4 Minor Members of the Solar System Asteroids: Microplanets An asteroid is a small, rocky body whose diameter can range from a few hundred kilometers to less than a kilometer. Most asteroids lie between the orbits of Mars and Jupiter. They have orbital periods of three to six years. Irregular Orbits of Asteroids 23.4 Minor Members of the Solar System Comets Comets are small bodies made of rocky and metallic pieces held together by frozen gases. Comets generally revolve about the sun in elongated orbits. Comets • As they get close to the Sun the ices on their surface sublime • Best viewed in morning or evening skies Anatomy of a Comet Nucleus – <10mi. diameter (water, methane, ammonia) – Planetary “building block” which never got incorporated into a planet Anatomy of a Comet • Coma – Cloud of gas & dust produced by evaporation of the nucleus when warmed by the Sun – Can extend 60,000 miles Anatomy of a Comet • Tail – Coma material pushed back by the Solar Winds – Always points away from the Sun – Can stretch up to 1 A.U. long Anatomy of a Comet Lose about 1% of their mass with each pass by the Sun Comet’s Tail Points Away from the Sun 23.4 Minor Members of the Solar System Comets Kuiper Belt • Like the asteroids in the inner solar system, most Kuiper belt comets move in nearly circular orbits that lie roughly in the same plane as the planets. Oort Cloud • Comets with long orbital periods appear to be distributed in all directions from the sun, forming a spherical shell around the solar system called the Oort cloud. Oort Cloud Oort Cloud Extends ½ way to the nearest star – 50,000 A.U. • May contain 1,000,000,000,000 comets 23.4 Minor Members of the Solar System Comets Halley’s Comet • The most famous short-period comet is Halley’s comet. Its orbital period is 76 years. **add to the notes: Short-period is less than 200 years. Long-period is greater than 200 years 23.4 Minor Members of the Solar System Meteoroids A meteoroid is a small, solid particle that travels through space. A meteor is the luminous phenomenon observed when a meteoroid enters Earth’s atmosphere and burns up, popularly called a shooting star. A meteorite is any portion of a meteoroid that reaches Earth’s surface. 23.4 Minor Members of the Solar System Meteoroids Most meteoroids originate from any one of the following three sources: (1) interplanetary debris that was not gravitationally swept up by the planets during the formation of the solar system, (2) material from the asteroid belt, or (3) the solid remains of comets that once traveled near Earth’s orbit. Meteors