Can the ortho-to-para ratio of ammonia in comet be a probe for the initial temperature of the solar system?

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K23450
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0204:Astronomy, earth and planetary science, and related fields
• Research Institution: Hokkaido University
• Principal Investigator: Kitajima Kensei 北海道大学, 低温科学研究所, 博士研究員 (70845445)
• Project Period (FY): 2019-08-30 – 2021-03-31
• Keywords: 核スピン / オルソパラ比 / アンモニア / 硫化水素

Outline of Final Research Achievements

We measured the ortho to para ratios (OPRs) of molecular species containing hydrogen atoms desorbed from the extremely low temperature ice surface, and investigated whether the value could be a probe that reflects the ice surface temperature. If the obtained OPRs are different from the statistical weight (3/1), it is considered to reflect the ice surface temperature. However, recent H2O experiments suggest that the OPRs of photodesorbed molecules are always 3/1. Therefore, in this study, we measured the hydrogen-containing molecules such as H2S and NH3 in the same way, and confirmed the OPR of the photodesorbed molecules. As a result, the value was 3/1 as previously shown in H2O.

Free Research Field

地球惑星科学およびその関連分野

Academic Significance and Societal Importance of the Research Achievements

従来の天文学では氷表面から脱離した分子のO/P比は，分子生成時の氷の表面温度を反映した値であるとされてきた．その結果から太陽系初期温度が推定されてきた．しかし本研究では，氷表面から脱離した分子のO/P比は，氷表面温度によらず，統計重率(3/1)であるという結果が示された．これは，従来のH2Oの測定結果で示唆されたように，太陽系初期温度を分子のO/P比から推定する天文学的なアプローチを再検討する必要性を示している．