Unidentified infrared emission features in mid-infrared spectrum of comet 21P/Giacobini-Zinner
Unidentified infrared emission features in mid-infrared spectrum of comet 21P/Giacobini-Zinner
复制标题
21P/Giacobini-Zinner 彗星中红外光谱中未识别的红外发射特征
DOI：
10.1016/j.icarus.2019.113450
复制
发表时间：
2020
期刊：
影响因子：
3.2
通讯作者：
M.
中科院分区：
文献类型：
--
作者：
Ootsubo;T.;Kawakita;H.;Shinnaka;Y.;Watanabe;J.;& Honda;M.
21 P/Giacobini-Zinner彗星（以下简称21 P/G-Z彗星）是一颗彗星家族的彗星，也是十月天龙座流星雨的母彗星。如果来自彗星家族的流星体含有复杂的有机分子，如氨基酸，那么它们就是地球生命起源之谜的重要组成部分。2005年7月5日，我们使用8.2米斯巴鲁望远镜上的冷却中红外相机和光谱仪（COMICS）在中红外波段观测了21 P/G-Z彗星。在这里，我们报告了彗星21 P/G-Z的未识别的红外（UIR）发射特征，这可能是由于复杂的有机分子（脂肪族和芳香族烃），以及在其中红外低分辨率光谱中来自无定形/结晶硅酸盐和无定形碳颗粒的热发射。在21 P/G-Z彗星光谱中发现的~8.2 μm、~8.5 μm和~11.2 μm的UIR特征可以归因于被N或O原子污染的多环芳烃（或氢化无定形碳），尽管~11.2 μm的部分特征来自结晶橄榄石。在~9.2 μm处的另一特征可能来自脂肪烃。彗星21 P/G-Z富含复杂的有机分子。考虑到21 P/G-Z彗星中结晶硅酸盐的质量分数是典型的彗星，我们认为该彗星起源于一个巨行星（类似于木星和土星）的环星盘，那里比典型的彗星形成区（距太阳5-30 Au）更温暖，适合形成复杂的有机分子。来自环行星盘的彗星可能富含复杂的有机分子，如彗星21 P/G-Z，并可能通过直接撞击或流星雨为古代地球提供了前生物分子。
Comet 21P/Giacobini-Zinner (hereafter, comet 21P/G-Z) is a Jupiter-family comet and a parent comet of the October Draconids meteor shower. If meteoroids originating from a Jupiter-family comet contain complex organic molecules, such as amino acids, they are essential pieces of the puzzle regarding the origin of life on Earth. We observed comet 21P/G-Z in the mid-infrared wavelength region using the Cooled Mid-infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope on UT 2005 July 5. Here, we report the unidentified infrared (UIR) emission features of comet 21P/G-Z, which are likely due to complex organic molecules (both aliphatic and aromatic hydrocarbons), and the thermal emission from amorphous/crystalline silicates and amorphous carbon grains in its mid-infrared low-resolution spectrum. The UIR features at ~8.2 μm, ~8.5 μm, and ~11.2 μm found in the spectrum of comet 21P/G-Z could be attributed to polycyclic aromatic hydrocarbons (or hydrogenated amorphous carbons) contaminated by N- or O-atoms, although part of the feature at ~11.2 μm comes from crystalline olivine. The other feature at ~9.2 μm might originate from aliphatic hydrocarbons. Comet 21P/G-Z is enriched in complex organic molecules. Considering that the derived mass fraction of crystalline silicates in comet 21P/G-Z is typical of comets, we propose that the comet originated from a circumplanetary disk of giant planets (similar to Jupiter and Saturn) where was warmer than the typical comet-forming region (5–30 au from the Sun) and was suitable for the formation of complex organic molecules. Comets from circumplanetary disks might be enriched in complex organic molecules, such as comet 21P/G-Z, and may have provided pre-biotic molecules to ancient Earth by direct impact or meteor showers.