lecture12_ch9 - Causation vs. Correlaton • What is an...

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Unformatted text preview: Causation vs. Correlaton • What is an example of correlation? • What is an example of causation? Planets as Homes for Life Today… … Another way to go extinct …(but more Hollywood-style)? What do asteroids look like? Spot the new asteroid The discoverer named it after Bruce Springsteen …and that got backstage passes (Ian Griffin) 1 How are meteorites related to asteroids & comets? Gravitational interactions with planets have eliminated certain orbits in the solar system. (Fig 9.4) 2 Peekskill, NY: October 9, 1992 Park Forest, IL: March 26, 2003 Tetons: August 10, 1972 Meteor showers happen when we pass through dust trails left by comets Meteoroid: A chunk of rock that enters Earthʼs atmosphere Meteor: The bright tail of hot debris from the rock Meteorite: A rock from space that reaches Earthʼs surface Meteors in a shower appear to emanate from the same area of sky because of Earthʼ s motion through space Next meteor show: the Orionids (Oct 21, starting around 1 AM), the debris of Halleyʼ s Comet, in Orion. 3 What are comets like? A cometʼs tail forms as sunlight melts the ice, releasing gas and dust particles (Fig 9.9) Where do comets come from? Fig 9.8 Oort cloud: On random orbits extending to about 50,000 AU Have we ever witnessed a major impact? Kuiper belt: On orderly orbits from 30-100 AU in disk of solar system Fig. 9.13 4 Tidal forces tore comet apart during previous encounter with Jupiter Impact plume rises high above Jupiterʼs surface 5 RAR Did an impact kill the dinosaurs? Mass extinction at the K-T boundary Comet or asteroid about 10km in diameter approaches Earth 6 No dinosaur fossils up here Thin layer of iridium from impactor here Dinosaur fossils down here 7 “Droplets” of formerly molten rock found in iridium layer The Impact Threat: Real danger or media hype? Fig 9.23 Meteor Crater, Arizona: Impact of a 30 m object about 50,000 years ago, 1.2 km crater Chance in any year of the Earth being hit by 10 km asteroid: A. 1 in a million C. 1 in 100,000 B. 1 in 10 million D. 1 in 100 million Chances are… The probability of a 2-km (or larger) diameter asteroid killing you is about ~1 in 100,00040,000. The average time between civilization-threatening impacts is ~2 million years. Your chance of death by 10 km asteroid: A. 1 in a million C. 1 in 100,000 B. 1 in 10 million D. 1 in 100 million Fig 9.23 (From a Jan 15, 2004 article by D. Morrison, impact.arc.nasa.gov, about Spaceguard) 8 Jovian planets determine where asteroids and comets are today Has Jupiter affected life on Earth? They might protect Earth from most of bombardment Fig 9.24 Impacts: Life Friendly? • Planetary scientists suspect that early bombardment by comets may have supplied much of the Earth’s water. • Recent studies (2007) show that Hale-Bopp Comet’s water has much more deuterium (2H) than Earth water. • But a few “asteroid belt” comets have been found (2005) - these might have water more like Earth’s. Friendly for life: • • • • Carbon molecules Liquid water Source of energy (star, thermal) Some stability (low impact, slow climate change) • Longevity 9 ...
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This note was uploaded on 11/13/2011 for the course ISP 205 taught by Professor Donahue during the Fall '08 term at Michigan State University.

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