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ROCKS FROM THE SKY

ROCKS FROM THE SKY. ROCKS FROM THE SKY.

robertjwalker
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ROCKS FROM THE SKY

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  1. ROCKS FROM THE SKY

  2. ROCKS FROM THE SKY Momentary luminous streaks in the sky – shooting stars, or meteors – occur when metallic or stony objects originating in interplanetary space enter the earth’s atmosphere and their surfaces are heated to incandescence by friction with the air. Such objects range in size from dust particles to masses weighing many tons. Many of them are destroyed by friction-generated heat during their passage through the air. Those which survive and reach the earth are known as meteorites.

  3. Meteor in Orion

  4. ROCKS FROM THE SKY • Meteoroid: A small, solid rock in space • Meteor: The glowing trail of a meteoroid through the Earth’s atmosphere: A“shooting star”. • Meteorite: A part of a meteoroid that survived the passage through the earth’s atmosphere and fell to the surface.

  5. On the afternoon of November 20, 1954, Mrs. E. Hulitt Hodges of Sylacauga, Alabama, lay napping on her living room couch.* An explosion and a sharp pain jolted her awake. And she found that a meteorite had smashed through the ceiling and struck her left leg. Mrs. Hodges is the only person known to be injured by a meteorite. *Across the street from the Comet Drive-In Theater

  6. Astronomy Picture of the Day May 6, 2003

  7. “A NEAR MISS” • Asteroid 1989FC just missed the earth on March 22, 1989. • Closed approach ~700,00 km (twice as far as the moon). • Size ~ 500 meters • Speed ~ 44,000 mph • If it had hit, energy of explosion • 20,000 one-megaton H-bombs • Crater ~ 10 km across, 1 km deep • Odds for an impact • Every year the odds are one in some 100,000 of having a civilization-threatening impact.

  8. “ROCKS FROM THE SKY”First Acceptance • 1803 A spectacular fall in north France was investigated by the physicist J.B. Biot for the French Academy. He concluded that rocks fell from the sky. • J. B. Biot’s report is a historic document of science, presenting the evidence of observations and meteoritic fragments. • If there are falls, there should be craters. • Are craters volcanic or impact? • Meteoritic finds near craters argued for impact.

  9. President Thomas Jefferson (1743-1826) • After a friend tried to assure him that objects “fall from the sky” as two Yale Professors had concluded, he replied: “I would prefer to believe that two Yankee professors would lie rather than stones could fall from heaven.”

  10. Relative sizes of Sun and planets

  11. The Solar System Object % Mass Sun 99.85 Planets 0.135 Satellites 0.00005 Asteroids 0.0000002 Comets 0.01? Meteoroids 0.0000001? Dust Particles < 0.0000001 Solar Wind << 0.0000001

  12. The Titius-Bode Rule PlanetTitius-Bode RuleActual Distance (AU) Mercury 0.4 0.39 Venus 0.7 0.73 Earth 1.0 1.00 Mars 1.6 1.52 Missing Planet 2.8 2.77 (Ceres) Jupiter 5.2 5.2 Saturn 10.0 9.54 Uranus 19.6 19.18 Neptunea 28.8 30.06 Plutoa 77.2 39.53 • 0,3,6,12,24,48, 96 • Add 4 • Divide by 10 a The rule fails for Neptune and Pluto

  13. Asteroid Diameter (km) Ceres 1025 Pallas 583 Vesta 555 Hygeia 443 Interamnia 338 Davida 335 Cybele 311 Europa 291 Patientia 281 Euphrosyne 270 Juno 267 Eunomia 261 Bamberga 256 Camilla 252 Sylvia 251? Eugenia 250 Distribution of Asteroid Sizes DiameterNumber > 200 km 30 > 158 km 58 > 100 km 195 > 63 km 463 > 32 km 1100

  14. Earth Crossing Asteroids

  15. Meteoroids in a Swarm

  16. Principal Meteor Showers Meteor Night of Average Number of Meteors Swarm Maximum Visibility Visible per hour Quadrantids Jan. 3 30 Lyrids Apr. 22 8 Eta Aquarids May 4 10 Delta Aquarids July 30 15 Perseids Aug. 12 40 Draconids Oct. 10 a few Orionids Oct. 21 15 Taurids Nov. 4 8 Leonids Nov. 16 6 Andromedids Nov. 20 a few Geminids Dec 13 50 Ursids Dec. 22 12

  17. Most Fundamental Indication of a Crater’s Meteoritic Origin:Underground Melted, Crushed and Shattered Rock

  18. Diameter Approximate Diameter of Crater Of Asteroid (km) (Produced on Earth)(km) 1 10 2 20 3 39 5 50 10 90 15 125 20 160

  19. Consequences Size Damage Typical fatalities • m Fall rocks 0 (Peekskill) • m Air burst hundreds to thousands (Tunguska) 200 m Regional damage thousands to millions (Meteor Crater) 2 km Global damage 100’s of millions to (Civilization threat) billions 10 km Global catastrophe billions or extinction (Chicxulub)

  20. The Extinction of the Dinosaurs • On Earth, 65 million years ago, dinosaurs and other species were extinguished. • Hypothesis – sudden extinctions were due to impact of an asteroid with the earth. • Impact caused much dust into the atmosphere to block the sun for months. • This caused plants and animals to die, including the dinosaurs. • Evidence – world-wide soot layer has been found in rock 65 million years old. • (Similar to nuclear winter theories).

  21. Meteorite Falls A Total of 1800 meteorite falls are listed in the Hey Catalogue of Meteorites; of these, 785 are falls and 1015 are finds. But the Antarctic recoveries are changing these statistics rapidly. Recent Spectacular Falls: • Tunguska, Siberia, June 20, 1908 • Brilliant fireball set up air-compression waves detected around the world. Seismographs in Europe detected the interaction with the Earth. Trees were destroyed over an area 50 miles in size. A man was knocked down 80 km away. • Size ~ 60 meters • Mass ~ 100,000 tons • Totally exploded and vaporized just before impact • No crater, no pieces recovered. • Near Vladivostok, USSR, February 12, 1947 • Fireball as bright as the Sun • Impact produced 106 craters, up to 30 meters each. More than 23 tons of iron meteorite fragments found. • Illinois, USA, September 29, 1938 • Meteorite pierced the roof of a garage and the roof of a car and was found buried in the car seat. • Alabama, USA, 1954 • A woman was struck and injured.

  22. Tunguska 1908

  23. Meteorite Craters • Each century several meteorites strike the earth to produce craters more than 10 meters across. • Mass ~ 2 tons • Size ~ half meter • Barringer Crater (Winslow, AZ) • Crater Size 1300 meters across 180 meters deep Rim rises 45 meters • Fragments ~ 25 tons iron meteorites collected finds as far as 7 km • Age ~25,000 years • Velocity ~15 km/sec (Shocked and Shattered the Rock) • Impact Pressure More than 130,000 atmospheres (Diamonds in the Iron Fragments formed by shock pressure) Energy of impact for 0.1 second created heat that vaporized most of the meteor and the impact surface.

  24. Iron meteorites were probably the first to be used to construct primitive instruments and weapons. • Meteorites used as burial sacred objects by American Indians • Kept as sacred possession of an Alaskan tribe • Sacred stone at the Temple of Diana at Ephesus • A Black Stone enshrined ~ 600 A.D. in the Moslem Shrine at the Ka`aba in Mecca • When a meteorite fell at Ensisheim, France, in 1492 A.D., the Emperor Maximilian decided to go on a crusade. (Meteorite in Ensisheim Church). • Meteorites are now mostly in museums.

  25. Numbers • On a moonless night, one can see about one meteor every ten minutes (these will be within ~100 miles from the observer). • Over the whole Earth 25 million meteors per day can be visible. • During “meteor showers” 10 to 60 meteors per hour can be seen. • The Earth gains about 10,000 tons of matter per year from the meteorites (~30 tons per day). Most are small specks of dust, some are larger. • Meteors enter the Earth’s atmosphere at speeds of 10 to 60 km/sec ( A rifle bullet travels ~0.7 km/sec). • Large objects, ~10,000 tons, fall every few centuries (~ nuclear blast scale). • In 1972, an object of 1,000 tons just missed the Earth, skipping off the atmosphere, it was filmed and detected by reconnaissance satellites. • Impacts with “Comets” are rare (one per 100 million year?).

  26. Types of Meteorites Meteorite Type Percentage of all Falls Remarks Stony Carbonaceous chondrite 6 Most primitive, least altered material available from early solar system. Chondrite 80 Commonest type. Defined by millimeter-scale spherical silicate inclusions, sometimes glassy, called CHONDRULES. Tektites – glassy small objects. Achondrite 7 Most nearly like earth rocks. Lack of chondrules. Stony-Iron 1 Contain stony and metallic sections in contact with each other Iron 6 Nickel-iron material. Museum specimens are often cut, polished, and etched to show interlocking crystal structure. This table is based on meteorites called FALLS – those actually seen to fall.

  27. Radar Echoes from Meteor Trails • Discovered during World War II radar experiments. Developed at Jodrell bank, Manchester, UK. • Detection of echoes from ionized meteor trails ~100 km above ground, at low frequencies (30-100 MHz) • Observe meteors • day and night • clear and overcast • Determination of • Statistics • Velocities • Directions • Interest by amateur radio astronomers and engineers

  28. Lunar Craters • Pre 20th century theory Volcanic Origin Bubbles of Molten Surface (Degassing) • 1910 most scientists agreed that lunar craters were due to impact, since it follows from the processes of capture and accretion by which the solar system objects were formed. • If lunar craters are due to impacts, where are the craters on Earth? The Earth has not escaped meteoritic bombardment, but effects diminished due to erosion. The absence of an atmosphere on the Moon causes almost no erosion to take place. • By 1910 more than 32,000 craters were counted on the Moon.

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