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原始太陽系星雲の高温過程で形成されたコンドリュールの再現実験
Reproduction experiments of chondrules formed at high‐temperature processes in the protoplanetary disk
中村智樹 1，森田朋代 1，渡邉華奈 1, 小山千尋 2，木村勇気 3，三浦均 4, 土山明 5，織田裕久 2，下西里奈 2
Tomoki NAKAMURA1, Tomoyo MORITA1, Kana Watanabe1, Chihiro KOYAMA2, Yuki KIMURA3,Akira TSUCHIYAMA4, Hirohisa ODA2, and Rina SHIMONISHI2
東北大，Tohoku Univ.,
宇宙航空研究開発機構, JAXA,
3 北海道大, Hokkaido Univ.,
4 名古屋市立大学, Nagoya City University
5 立命館大, Ritsumeikan Univ.

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1. Introduction
Chondrules are small solid particle with a diameter of about 1 mm occur in primitive chondritic meteorites(Figure 1) and are the major component of solid particles that were suspended in the protoplanetary disk.
Chondrules are thought to have been produced by high‐temperature heating of the precursor dust in the nogravity conditions of the protoplanetary disk, followed by various rates of cooling, but the specific formation
mechanism has not been specified1‐3). The main reason is that the structure and the elemental distribution ofchondrules cannot be reproduced perfectly by ground‐based experiments. In this study, we aim to reproducechondrules in microgravity experiments in the ELF equipment.

Figure 1. Barred olivine chondrule.

Chondrules are classified into several categories based on their textures, and the chondrule that we will
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reproduce in this experiment is barred‐olivine (BO) chondrule (Figure 1). We chose this type of chondrule
because (i) it was formed by total melting of the precursor material, which clearly constrains the melting andcooling conditions in the experiment, and thus the high‐temperature phenomena that occurred in the nebula,(ii) it has a characteristic texture (Figure 1: barred olivine and glass between them, with an olivine rim
surrounding the whole structure). (iii) because it is easy to determine the success or failure of reproducible
experiments.
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Experiments at ELF

In this experiment, starting materials has chemical composition of BO chondrules in meteorites (Table 1). The
starting material is heated to a temperature (about 1700°C) to melt total and then cooled to approximately
700°C by various cooling rates (0.5 K/s to 100 K/s in the crystallization temperature range). The detailed coolingprofile will be determined basis on simulations based on phase field theory and the results of groundexperiments. In developing the experimental conditions, we would like to perform experiments that
reproduced perfectly the texture and compositional features as seen in natural BO chondrules. Table 2 is theupdated success criteria for our experiment.

Table 1. Chemical compositions of starting material.

Type I
Na2O

1.5mol %MgO

46mol %

Al2O3

4.5mol %SiO238mol %CaO

4.5mol %FeO

5mol %NiO

0.5mol %Table 2. Updated success criteria of our experiment.

Success

Criteria
To obtain the temperature history of the sample from melting tosolidification.

Minimum SuccessTo recover the solidified samples to the earth.
To obtain information on the internal structure and composition ofsamples solidified at different rates of cooling.
In addition to the above, one of the following must be possible The

Full Successolivine bar structure found in natural chondrules is formed. Formpart of the olivine rim structure. Investigate the effects of vibration on
the rim bar structure.
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In addition to the above, one of the following must be possible. RimExtra
Success

structures covering the entire chondrule can be formed. Rims ofdifferent thicknesses can be formed under different conditions.
Elemental fractionation between olivine (bar and rim structures) andglass can be reproduced.

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Summary

Chondrules are the major building blocks of the asteroids and the Earth, they are the most important solid
particles in the formation of the inner solar system bodies 1). Therefore, to uncover the chondrule formation
mechanism and the heat source is one of the most important issues in solar‐system science. If we canreproduce the BO chondrules perfectly in terms of texture and elemental distribution in our ELF experiments,
the obtained conditions for chondrule formation (e.g., cooling rate and surface vibration) will provide strong
constraints on the currently available many models of chondrule formation (Figure 2).

Figure 2. Relationship between chondrule formation conditions and corresponding formation models.

References
1)
2)
3)

Alexander, C. M. D. (2022). An exploration of whether Earth can be built from chondritic components, not bulk
chondrites. Geochimica et Cosmochimica Acta, 318, 428‐451. DOI: 10.1126/sciadv.ade2067
Hood, L. L., and Horanyi, M. (1991). Gas dynamic heating of chondrule precursor grains in the solar nebula. Icarus,93(2), 259‐269. doi.org/10.1016/0019‐1035(91)90211‐B
Connolly Jr, H. C., & Love, S. G. (1998). The formation of chondrules: Petrologic tests of the shock wave model.
Science, 280(5360), 62‐67. DOI: 10.1126/science.280.5360.6© 2024 by the authors. Submitted for possible open access publication under theterms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/li censes/by/4.0/).
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