Elucidation of origin of water on rocky planets using isotopic records in meteorites

• Project/Area Number: 19K14790
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 17010:Space and planetary sciences-related
• Research Institution: Hiroshima University (2020-2021); Japan Aerospace EXploration Agency (2019)
• Principal Investigator: Koike Mizuho 広島大学, 先進理工系科学研究科(理), 助教 (60836154)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Project Status: Completed (Fiscal Year 2021)
• Budget Amount: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2020: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000); Fiscal Year 2019: ¥2,860,000 (Direct Cost: ¥2,200,000、Indirect Cost: ¥660,000)
• Keywords: 分化隕石 / 小惑星 / 放射年代測定 / 二次イオン質量分析計 / ウランー鉛年代測定 / 安定同位体 / 揮発性元素 / 始原的隕石 / 局所非破壊分析 / ウランー鉛年代 / 安定同位体分析 / NanoSIMS / 惑星の水の起源

Outline of Research at the Start

地球や火星などの岩石惑星の環境進化を論じる上で、水の挙動の理解は欠かせない。惑星は、いつ・どこから・どれほどの水を獲得したのだろうか？この手がかりを与えるのが、かつての微惑星~原始惑星の欠片である小天体由来の隕石群である。本研究では、岩石惑星が水を獲得するプロセスの解明を目的に、隕石の揮発性元素安定同位体比と放射年代記録を利用する。複数種類の隕石群について、高精度酸素同位体分析、局所年代分析、局所塩素・水素同位体分析を組み合わせ、母天体の水の記録の復元を目指す。

Outline of Final Research Achievements

This study focused on geochemical records in the ancient differentiated meteorites, which are believed to have originated from remnant planetesimals or protoplanets. Rocky meteorite groups named howardite, eucrite, and diogenite (called HED) are considered as initial crustal materials of asteroid 4-Vesta, that recorded various processes among the rocky planets region. To understand the origin of volatiles and evolution process of rocky planets, I have conducted in-situ radiometric dating by a secondary ion mass spectrometer (NanoSIMS) along with petrological observations and stable isotopic analysis of several differentiated meteorites, including HED and other samples. Based on this study, it is suggested that the collisional rate of the rocky planets region was much higher at early stage and decreased monotonically. Major collisional events should have ceased by 4.15 billion years ago, inferring that supply of volatiles ended before that time.

Academic Significance and Societal Importance of the Research Achievements

小惑星起源の試料には、地球や月以前の記録が残されている。従来、月試料などの同位体記録から、地球を含む岩石惑星領域での天体衝突は約39億年前（形成から６－７億年後）に急激に増加したと予想されてきた。本研究から、小惑星帯における主要な天体衝突は約45億―41.5億年前という比較的早い段階で完了していたことが示され、岩石惑星領域における物質移動と供給時期について新たな知見が得られた。太古の天体衝突と物質供給は、地球や火星における原始海洋の形成や最古の生命誕生にも関わる問題である。本研究の成果は、地球を始めとする惑星古環境進化の解明に貢献すると期待される。

Research Products

• [Int'l Joint Research] The Open University(英国)
• [Journal Article] In-situ preservation of nitrogen-bearing organics in Noachian Martian carbonates (2020)
  • Author(s): Koike Mizuho、Nakada Ryoichi、Kajitani Iori、Usui Tomohiro、Tamenori Yusuke、Sugahara Haruna、Kobayashi Atsuko
  • Journal Title: Nature Communications Volume: 11 Issue: 1 Pages: 1988-1988
  • DOI: 10.1038/s41467-020-15931-4
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] The Importance of Phobos Sample Return for Understanding the Mars-moon System. (2020)
  • Author(s): Usui, T., Bajo, K., Fujiya, W., Furukawa, Y., Koike, M., Miura, Y. N., Sugahara, H., Tachibana, S., Takano, Y., and Kuramoto, K.
  • Journal Title: Space Science Reviews Volume: 216 Issue: 4 Pages: 49-49
  • DOI: 10.1007/s11214-020-00668-9
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Evidence for early asteroidal collisions prior to 4.15 Ga from basaltic eucrite phosphate U-Pb chronology (2020)
  • Author(s): Koike Mizuho、Sano Yuji、Takahata Naoto、Iizuka Tsuyoshi、Ono Haruka、Mikouchi Takashi
  • Journal Title: Earth and Planetary Science Letters Volume: 549 Pages: 116497-116497
  • DOI: 10.1016/j.epsl.2020.116497
  • Peer Reviewed / Open Access
• [Journal Article] Migration of D-type asteroids from the outer solar system inferred from carbonate in meteorites. (2019)
  • Author(s): Fujiya, W., Hoppe, P., Ushikubo, T., Fukuda, K., Lindgren, P., Lee, M. R., Koike, M., Shirai, K., and Sano, Y.
  • Journal Title: Nature Astronomy Volume: 3 Issue: 10 Pages: 910-915
  • DOI: 10.1038/s41550-019-0801-4
  • Peer Reviewed / Int'l Joint Research
• [Presentation] Uranium-lead dating of zircon and phosphate minerals in a highly-shocked eucrite Northwest Africa 13166 (2022)
  • Author(s): Sumiya, Y., Koike, M., Onishi, K., Kurokawa, A., Takahata, N., Asanuma, H., and Sano, Y.
  • Organizer: 53rd Lunar and Planetary Science Conference
  • Int'l Joint Research
• [Presentation] 火星の表層環境史解明に向けた局所窒素化学種解析 (2022)
  • Author(s): 大西健斗, 小池みずほ, 黒川愛, 住谷優太, 中田亮一, 菅原春菜, 臼井寛裕
  • Organizer: 第46回生命の起原および進化学会学術講演会
• [Presentation] 隕石の放射年代分析から探る小惑星の衝突進化史 (2021)
  • Author(s): 小池みずほ, 佐野有司, 高畑直人
  • Organizer: 第82回応用物理学会秋季学術講演会シンポジウム
  • Invited
• [Presentation] 火星における窒素の循環進化: ALH84001 の痕跡と将来展望 (2021)
  • Author(s): 小池みずほ
  • Organizer: 第22回惑星圏研究会(SPS2021)
  • Invited
• [Presentation] 火星隕石から探る火星の表層環境進化 (2021)
  • Author(s): 小池みずほ
  • Organizer: 生命の起原および進化学会2021年シンポジウム
  • Invited
• [Presentation] Investigation of “Martian nitrogen cycle” and its evolution: The case of a young meteorite, Tissint. (2021)
  • Author(s): M. Koike, R. Nakada, I. Kajitani, ,H. Sugahara, T. Usui
  • Organizer: JpGU-AGU Joint Meeting 2021
  • Invited
• [Presentation] In-situ detection of early Noachian nitrogen-bearing organics from Martian carbonates. (2020)
  • Author(s): M. Koike, R. Nakada, I. Kajitani, T. Usui, Y.Tamenori, H. Sugahara, A. Kobayashi
  • Organizer: JpGU-AGU Joint Meeting 2020
• [Presentation] In-situ detection of nitrogen-bearing organics in Noachian Martian carbonates: Implication for nitrogen- cycle on early Mars. (2020)
  • Author(s): M. Koike, R. Nakada, I. Kajitani, T. Usui, Y.Tamenori, H. Sugahara, A. Kobayashi
  • Organizer: Goldschmidt Conference 2020
  • Int'l Joint Research
• [Presentation] In-situ detection of the nitrogen-bearing organic materials in 4-billion-year-old carbonates from martian meteorite Allan Hills 84001. (2019)
  • Author(s): Koike, M., Nakada, R., Kajitani, I., Usui, T., Tamenori, Y., Sugahara, H., and Kobayashi, A
  • Organizer: The Ninth International Conference on Mars
  • Int'l Joint Research
• [Presentation] ALH84001 炭酸塩鉱物からの有機窒素化合物の検出 (2019)
  • Author(s): Koike, M., Nakada, R., Kajitani, I., Usui, T., Tamenori, Y., Sugahara, H., and Kobayashi, A
  • Organizer: 日本地球化学会 第66回年会
• [Remarks] （広島大学 論文プレスリリース）【研究成果】40億年前より古い大量隕石衝突の痕跡を発見
  • URL: https://www.hiroshima-u.ac.jp/news/59830
• [Remarks] Remnants of an ancient asteroid shed new light...
  • URL: https://www.eurekalert.org/pub_releases/2020-09/hu-roa092420.php
• [Remarks] 40億年前の火星の有機物を発見. 最先端の分析技術で最古の火星史へ迫る
  • URL: https://academist-cf.com/journal/?p=13534
• [Remarks] 4-billion-year-old nitrogen-containing organic...
  • URL: https://eurekalert.org/pub_releases/2020-04/tiot-4no042720.php
• [Remarks] 個人website
  • URL: https://sites.google.com/view/mizuhokoike/home?authuser=0