PTYS_411_511_2_cratering_mechanics_morphologies

PTYS_411_511_2_cratering_mechanics_morphologies - Impact...

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PTYS 411/511 Geology and Geophysics of the Solar System Shane Byrne – shane@lpl.arizona.edu Background is from NASA Planetary Photojournal PIA00094 Impact Cratering Mechanics and Morphologies
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PYTS 411/511 – Cratering Mechanics and Morphologies 2 Crater morphologies Morphologies of impacts rim, ejecta etc Energies involved in the impact process Simple vs. complex craters Shockwaves in Solids Cratering mechanics Contact and compression stage Tektites Ejection and excavation stage Secondary craters Bright rays Collapse and modification stage Atmospheric Interactions In This Lecture
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PYTS 411/511 – Cratering Mechanics and Morphologies 3 Where do we find craters? – Everywhere! Cratering is the one geologic process that every solid solar system body experiences… Mercury Venus Moon Earth Mars Asteroids
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PYTS 411/511 – Cratering Mechanics and Morphologies 4 Morphology changes as craters get bigger Pit → Bowl Shape→ Central Peak → Central Peak Ring → Multi-ring Basin Moltke – 1km 10 microns Euler – 28km Schrödinger – 320km Orientale – 970km
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PYTS 411/511 – Cratering Mechanics and Morphologies 5 Last stages of planetary accretion Many planetesimals left over Most gone in a ~100 Myr We’re still accreting the last of these bodies today Jupiter continues to perturb asteroids Mutual velocities remain high Collisions cause fragmentation not agglomeration Fragments stray into Kirkwood gaps
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PYTS 411/511 – Cratering Mechanics and Morphologies 6 The worst is over… Late heavy bombardment 3.7-3.9 Ga Impacts still occurring today though Jupiter was hit by a comet ~15 years ago Chain impacts occur due to Jupiter’s high gravity e.g. Callisto Next lecture will look at: Dating using impact craters Solar system history from the impact record
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7 How much energy does an impact deliver? Projectile energy is all kinetic = ½mv 2 ~ 2 ρ r 3 v 2 Most sensitive to size of object Size-frequency distribution is a power law Slope close to -2 Expected from fragmentation mechanics Minimum impacting velocity is the escape velocity Orbital velocity of the impacting body itself Planet’s orbital velocity around the sun (~30 km s -1 for Earth) Lowest impact velocity ~ escape velocity (~11 km s -1 for Earth) Highest velocity from a head-on collision with a body falling from infinity Long-period comet ~78 km s -1 for the Earth ~50 times the energy of the minimum velocity case A 1km rocky body at 12 kms -1 would have an energy of ~ 10 20 J ~20,000 Mega-Tons of TNT Largest bomb ever detonated ~50 Mega-Tons (USSR, 1961) 2007 earthquake in Peru (7.9 on Richter scale) released ~10 Mega-Tons of TNT equivalent Harris et al. p
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This note was uploaded on 01/01/2011 for the course PTYS/ASTR 411/511 taught by Professor Shanebyrne during the Spring '08 term at University of Arizona- Tucson.

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PTYS_411_511_2_cratering_mechanics_morphologies - Impact...

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