Liquid-like behavior of UV-irradiated interstellar amorphous ice and its physical properties

2019 Fiscal Year Final Research Report

• Project/Area Number: 16H04072
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Petrology/Mineralogy/Economic geology
• Research Institution: Hokkaido University
• Principal Investigator: Kouchi Akira 北海道大学, 低温科学研究所, 教授 (60161866)
• Project Period (FY): 2016-04-01 – 2020-03-31
• Keywords: アモルファス氷 / 紫外線照射 / 液化 / 粘性

Outline of Final Research Achievements

Amorphous ices including impurity molecules is the most abundant solid component of interstellar molecular clouds and the outer cold part of protoplanetary disks. Ultraviolet (UV) photon irradiation of amorphous H2O-dominated may play a key role in synthesizing complex organic matter, amino acids, sugars, and nucleobases. However, there has been no study on the physical properties of UV-irradiated ices. Therefore, we investigated the heating process of UV-irradiated ices using optical and electron microscopy. We found that UV-irradiated amorphous ices composed of H2O, CH3OH, and NH3 and of pure H2O show liquid-like behavior over the temperature ranges of 65 to 150 K and 50 to 140 K, respectively. This low-viscosity liquid-like ice may enhance the formation of organic compounds including prebiotic molecules and the accretion of icy grains to form icy planetesimals.

Free Research Field

地球惑星科学

Academic Significance and Societal Importance of the Research Achievements

これまで，アモルファス氷は固体であり，紫外線照射によって変化することはないと考えられてきた．しかし，本研究の発見によりこの常識は覆された．また，この結果は，液化した氷（水）中では光化学反応が格段に速く進むこと，これらの微粒子同士の付着成長が促進される可能性があることを示している．これまでの惑星科学の常識を見直す必要があることを示している．