Meteorites

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Meteorites

• Meteoroid in space
• Meteor in atmosphere
• Bolide, fireball very bright
• Trail observed
• Meteorite hits ground
• Stony, Iron, Stony-iron
• Fall
• Find
• Parent body

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Collecting

• Historical Reports
• Rocks from the sky? No way! Way!
• Collecting today
• Around known craters
• Antarctica
• Ocean floor
• Upper atmosphere (meteoritic dust)

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Fall Observations

• Brightness Size
• Train
• Sound
• Temperature
• Velocity
• 10-70 km/s
• Fragmentation

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Fall Rate

• Varies with planet, age of solar system
• Earth 107 109 kg/year
• Moon 4 x 106 kg/year
• Most common Micrometeorites
• Damaging impacts 1/year
• Serious damage Once/20 years
• More damage - rarer

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• Falls 95 Stony 4 Irons 1 St-I
• Finds 52 Stony 42 Irons 6 St-I
• Variety of meteorites
• Different sources/Differentiated source
• Indications of heating/melting
• Presence of volatiles no heating
• Breccia collisions
• Formation heating sorting (siderophiles vs
  lithophiles, chalcophile) breakup - fall

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Stony

• Chondrites 86
• Chondrules olivine, pyroxene, enstatite, etc.
• Most primitive
• Two groups
• Carbonaceous chondrites (5)
• Most primitive, lowest temperature, volatiles,
  low density, organics
• Black graphite (carbon), magnetite, etc.
• Outer asteroid belt
• CI 8-22 water, no chondrules
• CM, CV, CO less water, more chondrules
• Chemical variation as well

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Murchison Meteorite

• Fall September 28, 1969
• 100 kg collected
• CM type
• 92 amino acids
• 19 terrestrial

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• Ordinary Chondrites (81)
• Less water, carbon, more alterations
• Not too hot
• Formation 2.5 AU
• Classified by iron content/iron oxide content
• E (Enstatite), H (high iron), L (low iron), LL
  (low, low)

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• Achondrites (9 )
• No chondrules why?
• Like igneous earth rocks
• Common groups
• Diogenites, Howardites, Eucrites, Aubrites,
  Ureilites
• Differences in FeO, Ca-rich minerals, mineral
  ratios
• Asteroid Vesta a source?

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• Stony-Irons (1)
• Mix of stone/iron
• Transition region in parent body?
• Two main groups
• Mesosiderites chunks of metal in rock (breccia)
• Pallasites chunks of rock in metal (melt)

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Irons

• Actually Iron-Nickel mix
• Classified by Fe/Ni ratio, minerals
• Low Ni content forms kamacite
• High Ni content forms taenite
• Influences internal structures
• Types
• Hexahedrite
• 5 Ni (pure kamacite)
• Neumann bands

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• Octahedrites
• 6-14 Ni largest group
• Taenite, kamacite
• Widmanstatten pattern

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• Ataxites
• gt15 Ni
• no internal structure
• Other classifications based on chemical comp.

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Minerals

• Sphalerite
• Corundum
• Perovskite
• Hematite
• Magnetite
• Spinel
• Quartz
• Calcite
• Dolomite
• Gypsum

• Apatite
• Olivine
• Pyroxene
• Feldspar
• Plagioclase
• Orthoclase
• Zircon
• Serpentine
• Muscovite mica
• Etc.

• Taenite
• Kamacite
• Copper
• Sulfur
• Graphite
• Diamond
• Troilite
• Pyrite
• Chalcopyrite

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Parent Objects

• Asteroid Belt
• Spectra of asteroids similar to some meteorites
• Falls traced to asteroid orbits
• Comets
• Dust mainly
• Any big items?
• Moon
• Mars

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Martian Meteorites

• 34 MM out of 24,000 meteorites
• Isotope ratios, compositions
• SNCs
• 1996 Big NASA announcement
• ALH84001
• PAH (polycyclic aromatic hydrocarbons)
• Magnetite
• Fossils?

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Are we sure?
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Comets vs Asteroids

• Comets
• Icy
• Small
• Wild orbits
• Oort cloud

• Asteroids
• Rocky/metallic
• Large small
• Normal orbits
• Asteroid belt

Thats what we used to know. 1977
Chiron Asteroid or comet? Simple distinction
comets flare up, asteriods dont
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Whats out there?

• Comets
• Short period
• Plt200 years
• Kuiper Belt objects
• Oort Cloud objects (captured)
• Long period
• Pgt200 years
• Oort Cloud objects

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• Asteroids
• Grouped according to orbital parameters
• Atens
• Earth crossers
• Inferior objects
• 500 known
• Apollos
• Earth crossers
• Superior objects
• 3000 known
• Amors
• Mars crosser
• 2500 known

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• Asteroid Belt
• Main location
• 30,000 known
• Many families (orbital parameters)
• Trojans
• L4, L5 of Jupiter
• 3000 known
• Cometary object
• Centaurs
• Between Jupiter-Uranus
• 250 or so

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• Trans-Neptunian Objects (TNOs)
• Classical Kuiper Belt (Cubewanos)
• 40-50 AU
• 1100 known objects
• Plutinos
• 23 orbital resonance with Neptune
• ¼ of TNOs
• Twotinos
• 21 orbital resonance with Neptune
• Rarer
• Scattered Disk Objects
• Edge of Kuiper belt
• Greater horizontal, vertical range
• Oort Cloud
• Edge of Kuiper belt 50,000 AU
• Millions of objects likely

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Taxonomy

• Classification based upon spectrophotometry
• IR spectra mainly
• Colors, composition, albedos
• Tends to be arranged by distance
• Not universally agreed upon

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• E-types
• Enstatite, forsterite rich
• High albedo (gt.3)
• Source of enstatite achondritic meteorites?
• S-types
• Silicaceous (stony)
• Olivine, metal, pyroxenes
• 17 of asteroids
• Moderate albedo ( .15)
• Pallasite meteorites?

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• Q-types
• Olivine, pyroxene, metals
• High albedo
• Chondrite meteorite (H, L, LL)
• M-types (for metals)
• Fe-Ni mix
• Moderate albedo
• Third largest asteroid group
• Iron meteorites
• V-types (for Vesta not Vendetta)
• High albedo
• Similar to S-types, but more pyroxene, feldspar
• Basaltic achondritic meteorites

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• R-types
• Olivine, pyroxene, maybe plagioclase
• Between A, V type
• High albedo
• Achondritic meteorite
• A-types
• Olivine
• High albedo
• Achondritic, pallasite meteorites

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• C-type (for carbon)
• Main type of asteroid, 75
• Beyond 2.7 AU
• Very low albedo (lt.1)
• Water in minerals, organics, carbon, OH,
  silicates
• Reddish color
• CI, CM meteorites
• B-type
• Like C, but not as red
• Low albedo
• Water, OH, silicates, carbon, organics
• Altered CI, CM meteorite

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• F-type
• Like B, but lacks water features in spectra
• Very low albedo
• Altered CI, CM
• G-type
• Like C, but with additional spectral features
• Phyllosilicate minerals (clays, micas)
• Altered CI, CM
• P-type
• Organic rich silicates, carbon, anhydrous
  silicates, reddish color
• Very low albedo
• C meteorites (but dry)

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• D-type
• Organic rich silicates, carbon, anhydrous
  silicates, water-ice interior?
• Trojans like this
• Water on surface?
• Very reddish
• Very low albedo
• Dry C-meteorite
• T-type
• Dark, featureless spectra
• Similar to P, D-types
• Very low albedo
• OH, silicates, carbon, organics,
• Altered CI, CM meteorites

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• Trends with distance
• Rocky/Metallic ? Carbon/Ice rich
• High albedo ? low albedo
• Asteroids ? Comets?
• Redder with distance (organics)
• Trojans, Centaurs, TNO also reddish
• Historical Clues
• 2.5-2.7 AU, Carbon (soot) line
• 3-4 AU, Ice line

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Comet/Asteroid Characteristics

• Limited up close observations
• Halley, Tempel, Wild 2
• Gaspra, Ida, Mathilde, Eros, NEOs
• Deep Impact and Stardust

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Comets

• Dirty iceballs?
• Water 50-80 of mass
• NH3, CH4, CO2 ice as well
• Few km in size
• Cratered, irregular shapes
• Low albedo Carbon, organics

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• Core activation
• 5 20 AU flare-ups
• 3 AU, Coma formation hydrogen cloud, 106 km
• Jets fissures?
• Tails
• Type I Gas, Ion
• Type II Dust
• Gases in coma, tail
• Dust - CHON

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• KBO, Centaurs, etc
• Larger than comets though rarer
• 35,000 KBO between 100-300 km
• 108 109 objects sized 1 km
• Fragile comets
• Meteor showers

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Asteroids

• Not exactly like meteorites
• Few meters 1000 km
• Density varies with type
• C-types, 1200 kg/m3
• M-types, 4000 kg/m3
• Lower than that of meteorites why?
• Moderate rotation rates correlated with size
• Slow retain surface material (regolith)

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Mathilde C-type
Ceres G-type
Vesta V-type
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Ida Dactyl S-type
Kleopatra M-type
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Eros
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Shoemaker-Levy 9

• Discovered March 24, 1993
• 21 pieces
• Not gas, but dust
• July 1992
• Inside Jupiters Roche limit
• July 1994
• Perijove lt Jupiters radius
• IMPACT!

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• Impact velocity 60 km/s
• Temperature 10,000 K
• Water vapor, sulfur vapor, sulfur compounds
  comet or asteroid?
• Dark markings on Jupiter carbon?
• What was it?

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Tunguska
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