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Transcript
ASTR 100 Lecture 13: Comets, Kuiper Belt, Oort Cloud Today: The rest of the solar system and the formation of the solar system Start Ex. 5 Friday: The formation of the Solar system …Ch. 6 And our Sun …Ch. 10 Kuiper belt, Oort cloud, and the comets whom they hath begat Summary: Comets: structure, orbits, and origin, Meteor showers Kuiper belt: An outer, icier, version of the Asteroid belt Oort cloud: An outer, icier, version of the Kuiper belt Comets observed throughout history, but usually attributed to supernatural origins 1577 Tycho Brahe showed they’re in “the heavens” 1705 Sir Edmund Halley showed one obeyed Newton’s/Kepler’s laws Some regular visitors, some one-hit wonders SOHO spacecraft has discovered 1600 comets in the last couple of years http://www.youtube.com/watch?v=1-dE_W8Nms0 …what are they made of and why are they so pretty Comet composition: Dirty snowballs which melt as they get close to the Sun. “Evaporating volatiles and dust” Comets have a (tiny) nucleus and three (giant) tails: 1) Plasma tail - evaporating gas, ionized by solar wind 2) Dust tail - unstuck as comet melts 3) Debris tail - bigger particles left in wake of the comet ~ 1AU http://www.youtube.com/watch?v=PeMhqyMPOaI http://www.youtube.com/watch?v=xbXlMFHYd0A Earth passes through the debris tail = Meteor shower Named after the constellation the meteors appear to be coming out of http://www.youtube.com/watch?v=S_jdfyp8pL0 Where do they come from? The Story of Pluto …Pluto’s a little weird. 1990’s: More Plutos…. 1930: A new planet! 2006: Pluto reclassified as a “dwarf planet” Dwarf planets have squished themselves spherical but have not cleared their orbital paths of stuff The Kuiper belt: The stuff in Pluto’s path Icy (frozen volatiles) bodies arranged in a doughnut shape from 30-(100) AU The Kuiper Belt can’t be the source of all comets Some comets have really high inclinations, up to 90 degrees from the ecliptic Oort cloud possibly formed from material ejected from the formation of the solar system Like 1 Trillion snowballs thrown out of the SS, being pulled back in by gravity Sounds like there should be a lot of comets. Where do they go? 1) They can totally evaporate: Quadrantids (in Jan) Delta Aquarids (in July/August) Have no associated comet 2) They hit stuff: More mass, more gravity, more likely that you’ll get hit We have seen a Jovian planet, capture and rip apart a comet, Comet Shoemaker-Levy 9, in 1994 http://www.youtube.com/watch?v=DgOTcIfU75Y “Capture” comets part of the story of planetary rings. Must be universal. Once collisions or tides make a debris field, it maintains itself by “grinding down” through more frequent collisions and “catching” new stuff Features of rings: Gaps, “ringlets”, gap and shepherd moons Metallic and rocky meteorites leave behind debris 1908 Tuguska Event had no debris… Comets may be responsible for Earth’s abundant water. Thank you, comets. How do we know? 1) Sending probes 2) Earth-based telescopes (Spectroscopy) 3) Historical sources Giotto 1986 Stardust 2004 Deep Impact 2005 http://www.youtube.com/watch?v=XKls-sN56Jk http://www.youtube.com/watch?v=dryvDlB1hWA Deep Impact 2005 Comet Tempel 1 Key terms: Comet, dust tail, plasma tail, Kuiper Belt, Oort cloud, Meteor shower, Centaur, Kuiper Belt Object (KBO), Key Ideas: What are the features and basic composition of a comet? How do the Jovian planets and Sun protect us from comet impacts? What are the two main sources of comets? The properties of Kuiper belt and Pluto Properties of the (alleged) Oort cloud What causes meteor showers? How do we know?