L7GH09Small_SS_bodies_I_Meteors_and_Mete

L7GH09Small_SS_bodies_I_Meteors_and_Mete - Small SS Bodies...

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January 27, 2008 meteors I Small SS Bodies I: Meteors and Meteorites • Lecture topics: meteors and meteorites, their physical properties, origin, age, connections… • Text readings: Chapter 7 pp 180-182; chapter 6 – all, esp. pp. 128-144 meteorite fall in 1492!
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January 27, 2008 meteors I Announcements • Details of research assignment available on webpage; more information in lecture next Tuesday The Structure of Early-Type Galaxies from the ACS Virgo and Fornax Cluster Surveys: Cores, Stellar Nuclei and Supermassive Black Holes Laura Ferrarese University of Victoria
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January 27, 2008 meteors I Fireball in SW Australia Question: What is the meteor observer’s best tool? Answer: Video cameras and phones!
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January 27, 2008 meteors I Meteor sizes • Consider a meteoroid (radius R, density ρ M , mass M=4/3 ( π R 3 ρ ) entering the atmosphere (density ρ a ) at some speed v ¾ the meteor must clear a path through the atmosphere to move forward – i.e. push air out of the way. ¾ this process both slows and heats the meteor vdt π R 2 R v M v R dt dv M a a ρ ρρ π 4 3 2 2 2 = momentum lost by the meteor is transferred to the atmosphere
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January 27, 2008 meteors I Ablation The slowing of the meteor also means an energy loss which results in heating of both the meteor and the air around it. Thus the brightness of a meteor is related to the mass-loss rate i.e. QdM ≈Λ dE k Q= energy required to cause ablation of mass dM ~ 0.8-2x10 7 J/kg Λ = fraction of energy loss that goes into ablation/sublimation Although the fall through the atmosphere heats a meteor, this heating penetrates only the outer mm-cm and leaves the interior very cool. Q v R dt dM a 2 3 2 ρπ Λ
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January 27, 2008 meteors I Meteoroid Breakup When will a meteor disintegrate, before it hits the ground? depends on internal “strength” of the body as well as velocity if v~10km/s, the kinetic energy is E K ~10 eV per atom – more than enough!
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January 27, 2008 meteors I Example: meteor sizes From film footage of a fireball you estimate a meteor’s initial velocity to be 20 km/s. When it disappears from view, 3 s later, it is traveling at a velocity of about 10 km/s. Assume it is traveling roughly horizontally, at an altitude where the
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This note was uploaded on 04/15/2009 for the course PHYS 275 taught by Professor Harris during the Winter '09 term at Waterloo.

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L7GH09Small_SS_bodies_I_Meteors_and_Mete - Small SS Bodies...

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