meteorite impacts

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Meteorite impacts. Comparative energies. No human in past 1,000 years has been killed by a meteorite. Direct observations of meteorite impacts. Tunguska, Siberia, 30 June 1908…a big bang above the Earth’s surface Shoemaker-Levy 9, July 1994…impacts hitting Jupiter. - PowerPoint PPT Presentation

TRANSCRIPT

  • Meteorite impacts

  • Comparative energiesNo human in past 1,000 years has been killed by a meteorite

  • Direct observations of meteorite impacts

    Tunguska, Siberia, 30 June 1908a big bang above the Earths surface

    Shoemaker-Levy 9, July 1994impacts hitting Jupiter

  • Direct observations of meteorite impactsIn 1954, a 5-kg meteorite crashed through a house in Alabama

    the object bounced off a radio and hit the owner in the head

  • Effects upon children

  • Indirect evidence of meteorite impactsPreserved craters on the continents, mainly the oldest parts (shields)

    Lac cratre in northern Qubec is a simple crater

    its rim diameter is 3.4 km, it is 250 m deep, and it is 1.4 Ma in age

  • Location map of some impact craters seen at the surface

  • Lac cratre

  • Meteor crater in Arizona is another simple crater showing rim ejecta

  • ManicouaganThe Manicouagan crater in Qubec is a spectacular example of a complex crater

    Its original rim has been removed by erosionthe current diameter is 100 km

    It has an uplifted central core and outer rings, which are filled by a lake

    Its age - 210 Ma - coincides approximately with a large extinction at the end of the Triassic period

  • St. Lawrence RiverManicouagan

  • Central uplift

  • Asteroids and the Asteroid BeltThe Asteroid Belt lies between Mars and Jupiterthere are about 4,000 objects

    As asteroids collide with one another, they fragment and send pieces into near-Earth orbits

  • AsteroidsAsteroids are rocky fragments (diameter 10m to 1000 km) which either:

    failed to consolidate into a planet, or

    represent remnants of a fragmented planet

  • AsteroidsMetallic: some stony types are strong and hard and may hit the Earth.

    Weak, friable types likely will explode in the atmosphere at high altitudes.

  • CometsComets come from the far reaches of the Solar System (outer solar system, kuiper Belt and in the Oort Cloud).

    They mainly consist of frozen water, carbon dioxide, or both with admixed small rock fragments and dust, thus are referred to as dirty icebergs or dirty snowballs

    They have highly elongate, elliptical orbits which bring them close to the Sun

  • CometsThe tail of the comet is produced as ices melt and gases and dust particles are shed from the object.

    Generally explode in the atmosphere at high altitudes.

  • Comet West, 9 March 1976

  • Comet P/Shoemaker-Levy 9, July 1994This comet was first detected on 24 March 1993

    It was broken apart by a close pass to Jupiter on 7 July 1992Hubble image,1 July 1993

  • The sequence of eventsThe collision of the comet with Jupiter occurred over several days, 16-22 July 1994

    It was the first collision of 2 solar system bodies ever observed

    At least 20 fragments hit Jupiter at speeds of 60 km/second

  • EnergiesFragment A struck with energy equivalent to 225,000 megatons of TNT, the plume rising to 1000 km

    Fragment G was the biggie, with 6,000,000 megatons TNT energy and a plume rising to 3,000 km

    Fragment G (and K, L) created dark impact sites whose diameters were at least that of Earths radius

  • Other definitionsMeteor: light through the sky. Most meteors are destroyed in Earths atmosphere.

    Meteoroid: matter revolving around the Sun or any object in planetary space too small to be called an asteroid or a comet

    Meteorite: a meteoroid which reaches the surface of the Earth without being vaporized

  • Stony meteorites (94% of all meteorites)Two types:

    Chondritescontain chondrulesthey are very old and primitive

    Achondritesno chondrulesPhoto of a carbonaceous chondrite (carbon-bearing)

  • Types of meteorites derived from asteroidsAchondrites have a metallic core and stony silicate mantle

    As asteroids fragment, both metallic and silicate pieces are producedMetallic coreStony silicate mantle

  • Iron meteoritesThese consist of nearly pure metallic nickel and iron

    This photo shows an iron meteorite named ARISPE

  • Stony-iron meteoritesThese are a mixture of the previous two types

    Often they are fragmental, suggestive of violent processes

    This stony-iron meteorite is named ESTHER

  • Impact events1. Probabilities

    2. Nature of the event

    3. Consequences

    4. Mitigation

  • 1. Probabilities of a collisionWhat are the chances of a large meteorite hitting Earth?

    As of 2003, ~700 objects with diameters > 1 km known to have orbits which intersect that of Earth

    And 30 new objects are discovered each year, with the search only 8% complete!

  • Probabilities - ZebrowskiZebrowski shows that, on average, collisions of 1 km-diameter objects occur every 250,000 years

    Such an impact is sufficient to wipe out most of the human populationFrom Zebrowski (1997)

  • Probabilities - CourtillotIs Zebrowskis estimate too high? Courtillot suggests it is about 1 Ma between events

    In any case, you can see that these events are both very rare and very destructiveFrom Courtillot (1999)

  • 2. Nature of the event

    Impact cratering is an important process in the history of Earth and other planets

    107 to 109 kg of meteoritic flux strikes Earth each year, mostly in the form of dust

  • Impact events

    The cratering process is very rapid

    Since the objects travel so fast (4-40 km/second), a huge amount of energy is transferred upon impact

  • Cratering A blanket of ejecta is dispersed around the crater

    rock is fractured, crushed, and broken

    In large impact events, the rock can even be vaporized (depending on the type of rock)

  • Cratering (continued)

    Very high pressures are reached, resulting in shock metamorphism (pressure-temperature increases)

    After the initial compression comes decompression, which may cause the rock to melt

  • Simple craters are basically simple bowls

    With time, the ejecta blanket outside the crater is erodedEjecta blanketfracturingBroken rock

  • Central upliftComplex craters are generated by rebound of the central core

    This core, as it decompresses, may meltmelt

  • There are about 200 large, well-preserved impact craters worldwideBUT>>200 impact events during Earths historyThis map shows both SURFACE and SUB-SURFACE examples

  • Consequences of a large impact event

    These would apply for an object of about 1 km or larger

    Actually, you may not want to hear the list of death and destruction (or maybe you do)...

  • Consequences 1

    A base surge, similar to a volcanic pyroclastic flow, will be generated by the impact

    For a terrestrial impact, rock will be pulverized and/or vaporized, sending up huge amounts of dust into the stratosphere

  • Consequences 2For an oceanic impact:

    huge amounts of water will be vaporized

    Global tsunamis will be generated, which will ravage the Earths coastlines

  • Consequences 3

    In the short term, global wildfires will be generated by the impact event

    These fires will burn uncontrollably across the globe, sending more soot, dust, and gas into the stratosphere

  • Consequences 4All this suspended dust and soot will cause global winter and global darkness

    Acid rains will fall

    Crops will fail catastrophically

    The end result will be MASS EXTINCTIONS

  • Consequences 5One last interesting point:

    The impact likely will trigger devastating quakes around the globe, especially where tectonic stresses are high (i.e., plate margins)

    Volcanism (flood basalts) may occur on the opposite side of the globe from the impact, as a result of shock waves travelling through the center of the Earth

  • From Murck et al. (1996)

  • MitigationThe problem is the possibility of little or no warning

    There are proposals to use nuclear weapons and satellites to shoot down or destroy such killer objects

    For further edification, rent Armegeddon from Blockbuster (1998)

    Good subject for a paper !

  • Two case studies

    Tunguska 1908, Russia

    The Cretaceous-Tertiary extinction, 65 Ma

  • Tunguska, Russia, 30 June 1908Something big seems to have exploded in the atmosphere

    The exact cause is uncertain, but we suspect a comet or a meteorAerial view of Tunguska Natural Reserve

  • What happened?The objects entry appeared to be at an angle of 30-35

    The object shattered in a series of explosions at about 8 km altitudeTree blowdown from the explosions; Note parallel alignment of the trees

  • Big firesIn the central region, forests flashed to fires which burned for weeks

    a herd of 600-700 reindeer was incinerated

  • Aligned treesTrees were felled in a radial sense

    About 2,000 km2 were flattened by the blasts

  • What happened?Our best scientific guess is that it was part of a comet 20-60 meters in diameter

    no crater was found

    and no meteoritic debris has been foundFelled trees aligned parallel to each other

  • Area of devastation superimposed on a map or Rome. Yellow=charred trees; Green=felled treesThe lack of a crater suggests disintegration above the surface of the Earth

    The lack of solid debris implies a comet rather than an asteroid

  • A global view

    Soot from the fires circled the globe, producing spectacular sunrises and sunsets for months afterward

    The Tunguska event was the largest known comet/asteroid event in the history of civilization