Where do meteorites come from? Well-photographed meteors which have produced meteorites: Pribram, Czechoslovakia1959H5 Lost City, Oklahoma1970H5 Innisfree, Alberta1977LL5 Peekskill, New York1992H6 Tagish Lake, British Columbia2000CM1 Tagish Lake fireball
Meteoroid orbits: aphelia between Mars & Jupiter (asteroid belt) Jupiter Mars
Spectral reflectance of various meteorites & asteroids
How do meteorites get to the Earth? (1) Perturbations by Jupiter can put asteroidal material into Earth-crossing orbits (Kirkwood gap clearing). (2) The Yarkovsky Effect can cause rotating m-sized objects to spiral inwards to (or outwards from) the sun. Cosmic-ray exposure (CRE) ages of meteorites (~1 Ma to ~0.5 Ga) give travel time needed for m-sized object-- consistent with Yarkovsky Effect
Meteorites: different types DesignationProportion of metal & silicate Stony>> 50 % silicate Stony-iron ~ 50% metal, ~ 50% silicate) Iron>> 50% metal alloy
Meteorite types & parent bodies # parent DesignationClass & rock typesbodies* Stonychondrites: agglomerate> 13 Stonyachondrites: igneous, breccia> 8 Stony-ironpallasite: igneous> 3 Stony-ironmesosiderite: meta-breccia1 (2) Ironmany groups: igneous50-80? * as inferred from chemical & isotopic studies
Meteorites: different types DesignationType of rock Chondriteagglomerate-- never melted (stony) All elseigneous; impact breccias-- (stony, stony- melted at least once iron, iron)
Chondrites have “solar composition” for most elements
Chondrites most contain chondrules mm to sub-mm-sized objects formed as melted dispersed objects some contain refractory inclusions (CAIs) mm to cm-sized objects formed at high temperatures in solar nebula some contain pre-solar grains grains formed around other stars some contain pre-biotic organic matter
“Chondritic texture”: an agglomeration of chondrules and fine-grained matrix matrix chondrules 0.2 mm
Mesosiderite origin: collision of a stripped metal core & another differentiated asteroid?
Studies of meteorites provide evidence for: 1) widespread transient, high-T heating events in the solar nebula -- to form chondrules, CAIs 2) gas-dust chemical equilibrium in the solar nebula -- “equilibrium condensation model” valid 3) incomplete mixing & heating of dust in the solar nebula -- pre-solar material survived solar system formation!
Studies of meteorites provide evidence for: 4) short-lived heat sources in meteorite parent bodies -- many asteroids melted & differentiated -- many asteroids metamorphosed & aqueously altered -- short-lived radionuclides, induction heating (?) were important in early solar system 5) water in many meteorite parent bodies -- in the form of ice or hydrated materials -- water in some asteroids too
Studies of meteorites provide evidence for: 6) pre-biotic organic synthesis -- precursor materials for life formed in space! 7) impact & collision processes -- collisions important, probably even early in solar system -- asteroids may have been disrupted & reassembled
Studies of meteorites provide evidence for: 8) interplanetary rock-swapping -- we have martian & lunar meteorites -- this has implications for life