Big Impacts and Bio-Extinctions ASTR 2120 Sarazin
Final Exam Saturday, May 5, 9:00 am - noon ASTR 265 (classroom) Bring pencils, paper, calculator You may not consult the text, your notes, or any other materials or any person Exception: three 3x5 cards with equations only on both sides ~2/3 Quantitative Problems (like homework) ~1/3 Qualitative Questions
Final Exam (Cont.) Material: Final exam will cover the entire semester Chapters 4, 8-12, 20-24 Galaxies Cosmology, Solar System Extra emphasis on material not on first two tests Solar System Chapters 10-12 Homeworks 9-11 Know pc, AU, M solar, L solar, R solar, H 0, T CMB, planets in order
Final Exam (Cont.) Review Session: Wednesday, May 2 4-5 pm ASTR 265 (classroom)
Big Impacts and Bio-Extinctions ASTR 2120 Sarazin
Impacts: Three Key Discoveries 1960: Impacts cause most cratering (Shoemaker) 1960+: Impacts are inevitable and continuing 1980: Impacts can have global biological consequences (Alvarez et al.)
Impact Energetics Deposited energy = kinetic energy Velocity large, orbital velocity ~ 30 km/sec = 66,000 mph Mass large Result: Impact energy = 250 D 3 m tons TNT (D m is diameter in meters) Implies D = 4.3 m yields 20,000 tons TNT = Hiroshima D = 40 m yields 15 million (mega) tons of TNT = Barringer, Tunguska D = 10 km (10,000 m) yields 250 mega megatons
Frequency of Impact Events
Frequency of Impact Events Pea-sized meteoroids 10 per hour Walnut-sized meteoroids 1 per hour Grapefruit-sized meteoroids 1 per 10 hours Basketball-sized meteoroids 1 per month 50 meter diameter meteoroids 1 per century
Target Earth: Estimated Frequency 1 ton asteroid, 10 m crater: few per century 1 km asteroid, 10 km crater: few per million years 10 km asteroid, 100 km crater: every 100 million years Were the dinosaurs wiped out 65 million years ago by a big one?
Impacts and Global Biological Extinctions
Diameter: 110 mi Age: 65 million yr Impactor: 10 km diam Chicxulub Crater, Yucatan, Mexico
Impact Scales City Buster: 15-m diameter; 1 megaton TNT. H-bomb scale. Local effects. People Buster: 1-km diameter; 250,000 MT. Continental/hemispheric effects. Many humans die. Planet Buster: 10-km diameter; 250 MMT. Global effects. Major bio-extinction, including almost all humans.
Lifetime Personal Risks of Death Asteroid impact: 1/20,000 Commerical airline crash: same Tornado: 1/2 AI Nuclear power plant: 1/3 AI Poisonous snakes, spiders: 1/5 AI
Saving Earth with a Gravity Tractor
Origin of the Solar System ASTR 2120 Sarazin Our Solar System in Earlier Days?
Origin Facts to be Explained Orbits All in single plane = equator of Sun All revolve same direction (same as Sun rotation) Most orbits nearly circular Regular spacing (Bode s law?)
Orbits
Origin Facts to be Explained Orbits All in single plane = equator of Sun All revolve same direction (same as Sun rotation) Most orbits nearly circular Regular spacing (Bode s law?) Rotation of Planets Most prograde = same direction as orbit Terrestrial Jovian Composition vs. distance from Sun Terrestrial = dense rock = near Sun Jovian = less dense, gas, H, He = far from Sun
Origin Facts to be Explained Ice Worlds Comets Kuiper Belt Oort Cloud
Many icy objects in outer Solar System Eris
Kuiper Belt and Oort Cloud Realms of Ice
Origin Facts to be Explained Ice Worlds Comets Kuiper Belt Oort Cloud Asteroids, Meteorites Irons, Stones
Asteroids Ida and Dactyl ( moon of Ida)
Stone Iron
Origin Facts to be Explained Ice Worlds Comets Kuiper Belt Oort Cloud Asteroids, Meteorites Irons, Stones Cratering of planetary surfaces
Moon Mercury
Origin Facts to be Explained Ice Worlds Comets Kuiper Belt Oort Cloud Asteroids, Meteorites Irons, Stones Cratering of planetary surfaces Age of planets = age of Sun = 4.6 billion years Sun rotates slowly?
Origin of Solar System Originally, two theories Catastrophe Theory Planets formed due to collision of Sun with another star Nebular Theory Planets form as normal part of star formation, formed at same time that Sun formed
Tidal Theory for Origin of Solar System
Nebular Theory : Planets are By- Product of Normal Star Formation
Implications of Formation Theories Tidal Theory: planets RARE Nebular Theory: planets COMMON
Exoplanets Planetary systems are very common!
Proto-Planets around Stars Many systems known where planets appear to be forming along with stars Nebular theory appears to be correct
Star Formation Interstellar gas and dust Concentrated into interstellar clouds Smaller ones are ~100,000 AU ~ 1 ly in diameter Stars form in interstellar clouds
Interstellar Gas and Dust
Interstellar Cloud
Star Formation Interstellar gas and dust Concentrated into interstellar clouds Smaller ones are ~100,000 AU ~ 1 ly in diameter Stars form in interstellar clouds Gravity causes clouds to collapse to form rotating disks, star forms at center
Evidence for disks in star forming regions
Beta Pictoris Debris Disk (Infrared)
Nebular Theory for Solar System Solar Nebula = interstellar cloud of gas and dust, ~100,000 AU Gravity causes it to collapse