Meteorites Meteoroid in space Meteor in atmosphere Bolide, fireball very bright Trail observed Meteorite hits ground Stony, Iron, Stony-iron Fall Find Parent body Collecting Historical Reports Rocks from the sky? No way! Way! Collecting today Around known craters Antarctica Ocean floor Upper atmosphere (meteoritic dust) Fall Observations Brightness Size Train Sound Temperature Velocity 10-70 km/s Fragmentation 1
Fall Rate Varies with planet, age of solar system Earth: 10 7 10 9 kg/year Moon: 4 x 10 6 kg/year Most common Micrometeorites Damaging impacts: ~ 1/year Serious damage: Once/20 years More damage - rarer 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 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 2
Murchison Meteorite Fall September 28, 1969 100 kg collected CM type 92 amino acids 19 terrestrial 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) 3
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? 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) 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 4
Octahedrites 6-14% Ni largest group Taenite, kamacite Widmanstatten pattern Ataxites >15% Ni no internal structure Other classifications based on chemical comp. Minerals Taenite Kamacite Copper Sulfur Graphite Diamond Troilite Pyrite Chalcopyrite Sphalerite Corundum Perovskite Hematite Magnetite Spinel Quartz Calcite Dolomite Gypsum Apatite Olivine Pyroxene Feldspar Plagioclase Orthoclase Zircon Serpentine Muscovite mica Etc. 5
Parent Objects Asteroid Belt Spectra of asteroids similar to some meteorites Falls traced to asteroid orbits Comets Dust mainly Any big items? Moon Mars Martian Meteorites 60 MM out of ~24,000 meteorites Isotope ratios, compositions SNCs 1996 Big NASA announcement ALH84001 PAH (polycyclic aromatic hydrocarbons) Magnetite Fossils? Are we sure? 6
Comets vs Asteroids Comets Icy Small Wild orbits Oort cloud Asteroids Rocky/metallic Large small Normal orbits Asteroid belt That s what we used to know. 1977 Chiron Asteroid or comet? Simple distinction comets flare up, asteriods dont What s out there? Comets Short period P<200 years Kuiper Belt objects Oort Cloud objects (captured) Long period P>200 years Oort Cloud objects Asteroids Grouped according to orbital parameters Atens Earth crossers Inferior objects ~ 750 known Apollos Earth crossers Superior objects ~4800 known Amors Mars crosser ~4050 known 7
Asteroid Belt Main location +36,000 known Many families (orbital parameters) Trojans L4, L5 of Jupiter ~5700 known Cometary object Centaurs Between Jupiter-Neptune 450 or so Trans-Neptunian Objects (TNOs) Classical Kuiper Belt 40-50 AU 1150 known objects Plutinos 3:2 orbital resonance with Neptune (~39 AU) 20% of TNOs Twotinos 2:1 orbital resonance with Neptune (~48 AU) Rarer Scattered Disk Objects Centaurs, and Kuiper belt Greater horizontal, vertical range Oort Cloud Edge of Kuiper belt 50,000 AU Millions of objects likely 8
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Inclination Angle Inclination (i) 3/20/2013 60 50 Uranus Neptune Plutinos 40 Kuiper Belt 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Semi-major axis (AU) 60 50 40 Centaurs 30 20 10 SDO 0 0 20 40 60 80 100 120 140 160 180 200 Distance (AU) 10
Eris Taxonomy Classification based upon spectrophotometry IR spectra mainly Colors, composition, albedos Tends to be arranged by distance Not universally agreed upon 11
E-types S-types Silicaceous (stony) Olivine, metal, pyroxenes 17% of asteroids Moderate albedo (~.15) Pallasite meteorites? Q-types M-types (for metals) Fe-Ni mix Moderate albedo Third largest asteroid group Iron meteorites V-types (for Vesta not Vendetta) R-types A-types C-type (for carbon) Main type of asteroid, 75% Beyond 2.7 AU Very low albedo (<.1) Water in minerals, organics, carbon, OH, silicates Reddish color CI, CM meteorites B, F, G, P, D, T-type 12
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 Comet/Asteroid Characteristics Limited up close observations Halley, Tempel, Wild 2, Hartley 2 Gaspra, Ida, Mathilde, Eros, Itokawa, NEOs Deep Impact/EPOXI and Stardust 13
Comets Dirty iceballs? Water 50-80% of mass NH 3, CH 4, CO 2 ice as well Few km in size Cratered, irregular shapes Low albedo Carbon, organics Core activation 5 20 AU flare-ups 3 AU, Coma formation hydrogen cloud, 10 6 km Jets fissures? Tails Type I Gas, Ion Type II Dust Gases in coma, tail Dust - CHON 14
KBO, Centaurs, etc Larger than comets though rarer Should be ~35,000 KBO between 100-300 km 10 8 10 9 objects sized 1 km Fragile comets Meteor showers 15
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) Mathilde C-type Ceres G-type Vesta V-type 16
Ida & Dactyl S-type Kleopatra M-type Eros 17
Itokawa A close shave.. 2012 DA14 18
Shoemaker-Levy 9 Discovered March 24, 1993 21 pieces Not gas, but dust July 1992 Inside Jupiter s Roche limit July 1994 Perijove < Jupiter s radius IMPACT! 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? 19
Russia Part 1 - Tunguska 20
Russia Part 2 - Chelyabinsk Damage Coincidence 21
Chelyabinsk 22