Lect1 Intro to Comets (10-27-09)

Lect1 Intro to Comets (10-27-09) - HW due Thurs. Nov. 5th...

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HW due Thurs. Nov. 5 th Sections IV, V, VI VII and VIII from Chapter on Physics and Chemistry of Comets (pdf in website)
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INTRODUCTION TO COMETS
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OUTLINE I. Introduction: History, Nucleus, Coma, Tails, Sources II. Gas and Ice Composition Parent and Daughter Molecules New Parent Molecules Isotopic Ratios Noble gases Pre-solar Signatures in Comets III. Comets and Earth’s Water IV. Dust Composition V. Summary
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History From the Greek “ κομετ εσ ” (kometes). Long-haired ones. Ancient Greeks believed comets were atmospheric phenomena, part of the “imperfect” Earth and not part of the “perfect and immutable” heavens Somehow comets gained the reputation of being bad omens. Example: comet Halley’s apparition in 1066, bad omen for King Harold II of England (but good for William the Conqueror). I. INTRODUCTION
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A portion of the Bayeux Tapestry
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History (cont.) Today we know comets are “dirty icebergs” in orbit around our Sun Tycho Brahe, pioneer observational astronomer before the telescope was invented, could not measure parallax on the great comet of 1577 and concluded it had to be well beyond the Moon Edmund Halley in late 1600 calculates the orbit of three “great” comets and shows it’s the same one I. INTRODUCTION
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History (cont.) In 1950: Fred Whipple proposes the nucleus of a comet as an icy conglomerate or dirty iceberg Jan Oort concludes new comets originate in a spherical cloud ~1/3 distance to nearest star Kuiper and Edgeworth propose a reservoir of comets beyond Neptune I. INTRODUCTION
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History (cont.) In 1986 three spacecraft (two Soviet-French and one ESA) encounter comet Halley In 1992 the first member of the Kuiper Belt is discovered In 2001 the first US spacecraft (Deep Space 1) encounters a comet, Borrelly. In 2004 the Stardust spacecraft encounters comet Wild 2 and captures a sample of dust returned to Earth in 2006 In 2004 ESA’s Rosetta mission is launched toward comet 67P/Churyumov-Gerasimenko In 2005 the Deep Impact mission impacts comet Tempel 1 on July 4. I. INTRODUCTION
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Nucleus, Coma and Tails The Nucleus is where all cometary activity originates When a comet is far from the Sun it is an inert object When a comet approaches the Sun the ices in the nucleus sublimate and create a cloud of gas and dust called the coma Sunlight and the solar wind push the dust and gas away from the sun creating the tails I. INTRODUCTION
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Comet Hale-Bopp Ion Tail Dust Tail (Image by Elizabeth Warner on March 8, 1997) Coma
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A comet’s tail will always point away from the Sun
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Nucleus, Coma and Tails (Cont.) Our solar system formed about 4.6 billion years ago from the solar nebula. The planets and the Sun have undergone
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Lect1 Intro to Comets (10-27-09) - HW due Thurs. Nov. 5th...

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