Laboratory study for understanding the meaning of the nuclear-spin temperature of water in interstellar clouds, protoplanetary disks, and comets

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H06024
• Research Category: Grant-in-Aid for Young Scientists (A)
• Allocation Type: Single-year Grants
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: Hokkaido University
• Principal Investigator: Hama Tetsuya 北海道大学, 低温科学研究所, 助教 (20579172)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 星間塵 / 星間分子 / 核スピン温度 / アモルファス氷 / 核スピン異性体 / 彗星 / 原始惑星系円盤

Outline of Final Research Achievements

The nuclear-spin temperature of gaseous water (H2O) in space have been used to study the past formation temperature of H2O ice on interstellar dust. However, the relation between the formation temperature of H2O ice on the dust surface and the nuclear-spin temperature of gaseous H2O desorbed from the ice has yet to be explored experimentally. In this study, we report that the nuclear-spin temperature of gaseous H2O desorbed from ice at 10 K shows the high-temperature limit (> 50 K), even when the ice is produced in situ by hydrogenation of O2, a known formation process of interstellar H2O ice. This indicates that the nuclear-spin temperature of gaseous H2O in space cannot be used to deduce the past formation temperature of H2O ice on dust.

Free Research Field

地球宇宙化学

Academic Significance and Societal Importance of the Research Achievements

これまで，宇宙の水(H2O)の核スピン温度は「H2O氷が星間塵の表面で生成したときの温度を反映している（生成温度計）」と考えられてきたが，本研究によって「H2Oの核スピン温度からはH2O氷の生成時の温度環境を知ることはできない（生成温度計ではない）」ことが明らかになった．この結果は，これまでのH2Oの核スピン温度の観測結果すべてを再解釈する必要があることを示している．今後本研究の成果に基づいて，宇宙でどのようにしてH2Oが生成したのかについて理解が進むことが期待される．