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Chapter 9

Chapter 9 Asteroids.doc

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York University
Natural Science
NATS 1740
Randy Hoffman

Chapter 9 Asteroids, Comets and Dwarf Planets 9.1 Asteroids and Meteorites Why is there an asteroid belt? - Rocky planetesimals survived in the asteroid belt between mars and Jupiter because they did not accrete into a planet  Why didn’t another terrestrial planet form here instead? Jupiters role in the asteroid belt - Jupiters gravity through the influence of orbital resonances stirred up asteroid orbits and thereby prevented their accretion into a planet  Resonances arise whenever objects periodically line up with each other so gravity effects them over and over again in the same direction How are meteorites related to asteroids? The difference between meteors and meteorites • Meteor: flash of light caused by a particle entering our atmosphere at high speed not the particle itself • Meteorite: large enough to pass the atmosphere and leave an impression on the ground Types of meteorites • Primitive meteorites: simple mixtures of rock and metal sometimes also containing carbon compounds and small amounts of water  Nearly 4.6 billion years old • Processed meteorites: large asteroids underwent differentiation, made of mostly iron some are rocky  Few 100 million years younger than primitive - Most meteorites are pieces of asteroids and they teach us much about the early history of our solar system • Lunar meteorites: meteors from the moon • Martian meteorites: meteors from mars 9.2 Comets - Mostly composed of ice because they formed beyond frost line How do comets get their tails? - Most comets remain perpetually frozen in the outer solar system  Only a few enter the inner solar system where they can grow tails - Haleys comet orbits the sun every 76 years (last passed in 1986 returns 2061) Comet structure and composition • Nucleus: chunk of ice mixed with rocky dust and more complex minerals • Coma: leftover dusty atmosphere  Larger than the nucleus • Plasma tail: gas escaping through the coma • Dust tail: dust size particles escaping the coma - When a comet nears the sun, it ices can sublimate into gas and carry off dust creating the coma and long tails Comet tails and meteor showers
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