Impact3s - • Sources of ET debris • 1 Comets “dirty...

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Unformatted text preview: • Sources of ET debris • 1. Comets: “dirty snowballs” • Commonly around 15km diameter Deep impact probe collides with Comet Temple 1, July 4, 2005 T3:1a Comets come from the Oort Cloud and Kuiper Belt • Solar winds sublime ice ->tail • Comets “fall” into inner solar system - Earth crossing orbits • Comet Halley: 74 - 79 years • Comet Hale-Bopp (1997) back again in 2380 years • Comets: implications for development of life on Earth? • November every year: Leonid Meteor Shower • Tail of comet Tempel-Tuttle (33 year return time) • Creates a “band” of meteoroid debris (note: meteorite - an object that survives impact with Earth $ s surface) • 2. Asteroids • Smaller than planets, larger than meteoroids (meteoroids: sand - boulder size) • Common in a series of belts between Mars and Jupiter • Rates of meteoroid inFux • 100 000 million every 24 hours! • Most burn up entirely 60km above surface • Traveling at 11 - 30km / second (70 000 mph) • Atmosphere acts like a brick wall • Shallow angles - “skips” Grand Teton Fire Ball, August 10th 1972 3m diameter meteoroid Hiroshima after the bomb. Same scale of devastation that would have occurred if the Grand Teton Fireball had impacted a city on Earth • History of impacts • Early Earth - probably suffered multiple impacts - Craters eroded T3:2a- Evidence from inner planets / moon- What is different here? Craters on Mercury • Until recently (1960 $ s) impact on Earth believed to be “improbable” • Moon craters - extinct volcanoes • Gene Shoemaker • Large circular structures associated with ejecta, shocked quartz, iridium etc • Manicouagan Crater, Northern Quebec • Late Triassic - 75km diameter (probably 100km before glacial erosion) • At least 4 other impacts at SAME time • Including….. • Saint Martin Crater in Manitoba (100km diameter) • Rochechouart Crater, France (25km diameter) • Reassemble continents to late Triassic times • All craters line up along 22.8°N latitude (4 462km) • Impact of fragmented comet / asteroid • Periodicity of Mass extinctions • Raup and Sepkoski (1984) • 26-30 million year “extinction” periodicity T3:3a • Related to Oort Cloud? • Gravitational “Kicks” from… 1) Nemesis - companion sun • Red dwarf star - smaller, cooler than our sun • Black hole?...
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Impact3s - • Sources of ET debris • 1 Comets “dirty...

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