Impact3s - Sources of ET debris 1. Comets: dirty snowballs...

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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 22.8N 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 snowballs...

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