meteors and meteorites. “meteoroids” - still in space…
TRANSCRIPT
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Meteors and Meteorites
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“Meteoroids” - still in space…
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“Shooting Stars”
• Size of a pea
• velocities of 10’s km/sec
•~ 6/hour sporadic rate (any night)
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“Bolides” or “fireballs”
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Sometimes seen in daytime
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Sometimes break up
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Meteor “train” can persist
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If hit: “meteorites”
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Meteor showers occur when we cross paths of a broken up comet
Here the “Persieds” named …
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… named for constellation containing the radiant point
Leonids shown here or plotted…
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…plotted back to radiant in Leo
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Caused by perspective – the artist’s “vanishing point”
Driving in snow
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Major showers
Handout
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Leonids spectacular every 33 years
• Due to lumpiness in distribution of old comet within orbit
• This woodcut from 1833 – 100,000/hour
• My first chance – 1966
• Most recent 2000-2002-who saw?
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Meteors better after midnight
But…
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Meteorites: typesCarbonaceous
Stony
Iron-nickel
Iron
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Iron most commonly found but more stony meteorites more common!
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Widmanstatten patterns
these crystals take several millions of years to grow
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Stony meteorites – 93% of all meteorites
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Show chondrules (round stones) when cut and polished
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Stony-irons show a mix
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Carbonaceous chondrites
• this at right from 1969 Allende’ fall in Mexico
• Primordial in content
• Contain volatiles
• Organics
•Radioactive nuclei – 26Al may be from supernova that sparked the formation of our solar system
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Model to explain the variety
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Barringer crater in Arizona
1.2 km diameter, 25,000 years ago, 11 km/s = 20 Mton bomb
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Drilling found the rock
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41-mile diameter crater in Quebec
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Tunguska
Heard for 1000 km. Small comet? What if had happened 60 – 70 years later?
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Walter and Luis Alvarez found iridium clay layer at Cretacous-Tertiary boundary (65My ago)
Traced impact to …
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Chicxulub Impact structure• A bad day for dinosaurs
• Expect such hits every ~ 8 million years
• May find a kilometer within 10-20 years
• Need to look for 100-m objects
• Need a wakeup call?
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That’s all. Have a nice day!