Meteorites and mineral textures in meteorites. Tomoki Nakamura. Meteorites ~100 ton/yr Interplanetary dust ~40000 ton/yr.

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1 Meteorites ~100 ton/yr Interplanetary dust ~40000 ton/yr Meteorites and mineral textures in meteorites Tomoki Nakamura Челябинск Tohoku University Japan

2 Barringer crater (Arizona USA) 1275m diameter and 173m depth 30m size iron meteortie (parts of which are found as Canyon Diablo iron meteorite) hit the place 50K years ago. The high pressure upon impact made diamond from carbonaceous material and any life within 4km was extinguished.

3 Meteorite collection at Antarctica 2015 Tomoki found C chondrite

4 Asteroids parent body of meteorites

5 Meteorite-asteroid relationship reflectance spectra Reflectance (normalized) Wavelength (micron)

6 Solar nebula Early evolution of the inner solar system is recorded only in asteroidal materials. Small planetary bodies Asteroid-belt Kuiper-belt Short-peroid comet

7 Disk-shape gaseous nebula found around young stars in the Orion nebula They appear elliptical since each is tilted toward Earth at different angles. Disk-shape gaseous nebula commonly occurs around young stars and thus our Sun was also having such disk nebula

8 Interstellar molecular cloud The birth of solar system Interstellar molecular cloud low-temperature gas and small dust particles Solar nebula low~high temperature gas and dust particles

9 Presolar grains vs solar system material graphite Super nova Presolar period AGB star Presolar grains Time Diamond Molecular cloud 4.6Gyr Solar nebula Solar system period Chondrules at high temp region: Formation of solar system particles

10 Graphite Presolar grains SiC Diamond They are separated from primitive chondrites that escaped thermal process for 4.6 billion years. Concentrations are less than 1%.

Cubic Hexagonal Polytype distribution Cubic 3C 80% 2H/3C intergrowths 16% Hexagonal

11 Presolar SiC polytypes (Daulton et al. 2002) SiC grains from MurchisonPresolar 0.1μm 1μm 3C SiC is easily produced on commercial basis for polishing compounds. Cubic Hexagonal Polytype distribution Cubic 3C 80% 2H/3C intergrowths 16% Hexagonal 2H 2% 3C+2H is possible by condensation. Many 3C+ few 2H condense, no 6H condense is K.

12 What do we learn from isotope ratios of SiC? This is much more interesting in the case of SiC.

13 Xe isotope ratio of presolar SiC Xe in the solar system have 9 isotopes (124, 126, 128, 129, 130, 131, 132, 134, 136). But presolar SiC contains only five isotopes!

s process path in the Xe region (s-process = slow neutron capture + beta decay) Proton number atomic nucleus nuclear fusion + + Neutron number neutron capture

14 s process path in the Xe region (s-process = slow neutron capture + beta decay) Proton number atomic nucleus nuclear fusion + + Neutron number neutron capture neutron S process is one of neutron capture reactions (making heavy elements) taken place in stars. Only 128, 129, 130, 131, and 132Xe are produced by s process.

15 Presolar SiC was made around AGB stars SiC and AGB-star He shells Asymptotic Giant Branch: second time giant branch with 4 He exhaustion. Final phase of low- and middle mass star (<10 solar mass). Large mass ejection to outside results in formation of dust grains by condensation. Results from isotopes: AGB stars are one of parent stars of our solar system

16 First solar system material: chondrules (and CAIs) heating cooling Higher temperature heating Solid precursor (presolar grains) ~4.566 Bya Melting at high temperature (>1500K) Si enrichment Chondules (<1mm) High temperature regions

Barred olivine chondrules Product of total

Barred Olivine (BO) chondrules occupy ~5% of

(Grossman et al, 1988) Glass Olivine bar

Classic Barred Olivine 100μm open nicols One

17 Barred olivine chondrules Product of total melting. Barred Olivine (BO) chondrules occupy ~5% of all chondrules. (Grossman et al, 1988) Glass Olivine bar (Plate in 3D) crossed nicols Olivine rim Classic Barred Olivine 100μm open nicols One direction of parallel bars Bars and rim are single crystal Multiple Barred Olivine Multi-directions of parallel bars

18 Question How barred olivine chondrules were formed? To answer to this question, we need to experimentally reproduce barred olivine chondrules. Since 1980, many attempts have been made, but

19 Barred olivine chondrule reproduction experiments Lofgren and Lanier, (1990) Radomsky and Hewins, (1990) 500~2300 /h No BO chondrules are reproduced. Crystallization from wires and small supercooling are problems. 250~1000 /h

20 Barred olivine chondrule reproduction experiments Tsuchiyama et al., (2004) 1000 /h Heating in carbon capsule Very similar to BO chondrule, but olivine rim is not reproduced. Real BO rim

21 Levitated chondrule crystallization experiments (Tsukamoto et al. 1999) BO chondrules were crystallized from levitated melts in space Crystallization without any contact Large supercooling Radial pyroxene chondrules are reproduced.

22 Results of levitation experiments BO chondrule in Allende CV3 Experimental BO: 74.6 /s Much higher cooling rates are possible: ~ 100 /s vs ~1 /s (furnace) Much larger supercooling is possible: ~ 800 BO was produced, but still olivine rim is not reproduced.

convection and vibration of the surface induced by Ar

23 Why we cannot reproduce BO chondrule? Melt droplet Strong convection and vibration Strong convection and vibration of the surface induced by Ar gas used for levitation make crystallization of the rim difficult? Ar gas flow

24 Conclusions and implications Reproduction of olivine rims in BO chondrules requires crystallization at very static environments where surfaces of chondrules should stay very quiet. This conclusion constrains the formation mechanisms of BO chondrules. Shock wave formation model is probably less likely because in this model chondrules are heated by friction of H2 gas in the nebula. This induces strong convection and vibration of chondrule surfaces and makes olivine-rim formation difficult.

Dating. AST111 Lecture 8a. Isotopic composition Radioactive dating

Dating. AST111 Lecture 8a. Isotopic composition Radioactive dating Dating Martian Lafayette Asteroid with patterns caused by the passaged through the atmosphere. Line on the fusion crust were caused by beads of molten rock. AST111 Lecture 8a Isotopic composition Radioactive