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(150 Million km) Comet Hale-Bopp
19 NATURE of the Universe Astronomy - The Solar System Interplanetary Matter Comets orbit the Sun on highly eccentric orbits. As they approach the Sun near perihelion, they heat up and the ice on the outer surface is turning into gas. This creates the coma. The ion tail, made out of charged gas particles, always points away from the Sun. The particles in the dust tail tend to stay on Keplerian orbits around the Sun, resulting in the curved dust tail. Halley's comet looses about 0.25% of its mass during each perihelion. At this rate, it will vanish within the next 400 orbits, i.e. in less than 30,000 years. For comparison, the age of the Solar System is 4.6 billion years.
20 NATURE of the Universe Astronomy - The Solar System Interplanetary Matter Why do we still see comets if they are relatively short-lived (<40,000 year)? In 1950, Jan Hendrik Oort postulated that comets originate in a spherical cloud in the outer solar system, extending out to 50,000 AU (i.e. a quarter of the distance to the most nearby star). Passages of nearby stars are believed to disturb the Oort cloud to send comets into the inner solar system.
21 NATURE of the Universe Astronomy - The Solar System Some comets never return... Interplanetary Matter Observations of "Sun grazing comets" by the Solar and Heliospheric Observatory": 22 NATURE of the Universe Astronomy - The Solar System Interplanetary Matter Where do meteors ("shooting stars") come from? When comets break up, the debris spreads out along their orbit. Meteor showers happen when Earth crosses a part of the comet orbit filled with debris. Car trunk, after being hit by the 12 kg Peekskill meteorite in 1992.
23 see http://starchild.gsfc.nasa.gov/docs/StarChil...
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