Molecules Detected in Comet 21P/Giacobini-Zinner
Subaru Telescope | National Astronomical Observatory, Japan | 2019 Nov 18
Using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru Telescope, astronomers have detected an unidentified infrared emission band from comet 21P/Giacobini-Zinner (hereafter, comet 21P/G-Z) in addition to the thermal emissions from silicate and carbon grains. These unidentified infrared emissions are likely due to complex organic molecules, both aliphatic and aromatic hydrocarbons, contaminated by N- or O-atoms. Considering the properties of the dust and organic molecules, comet 21P/G-Z might have originated from the circumplanetary disk of a giant planet (like Jupiter or Saturn) where it was warmer than the typical comet-forming regions.
Comet 21P/G-Z is a Jupiter-family comet with an orbital period of about 6.6 years and is thought to be the parent body of the October Draconids meteor shower. Compared to other comets, this comet is peculiar in terms of its volatile content (depleted in carbon-chain molecules, NH2, and highly volatile species) and the properties of its dust grains, and is categorized as "G-Z type" (~6% of surveyed comets). Based on previous studies, it was proposed that comet 21P/G-Z originated in a different region than other comets, but we didn’t have any information about the specific region in the protoplanetary disk. A negative trend of linear polarization in the optical wavelength region is also reported for the dust continuum of comet 21P/G-Z. It is suggested that this negative wavelength gradient of polarization might be explained by a higher content of organic materials in the dust grains of 21P/G-Z. If complex organic molecules like amino acids are enriched in comet 21P/G-Z and in the meteoroids of the October Draconids, this meteor shower might have delivered complex organic materials to the ancient Earth. However, complex high-molecular-weight organic molecules have never been detected clearly in comets, except in comet 67P/Churyumov-Gerasimenko by the in-situ measurements of the Rosetta spacecraft. How much and how complex of organic molecules are contained in comet 21P/G-Z is still an open question. ...
Unidentified Infrared Emission Features in Mid-infrared
Spectrum of Comet 21P/Giacobini-Zinner ~ Takafumi Ootsubo et al
- Icarus 338:113450 (01 Mar 2020) DOI: 10.1016/j.icarus.2019.113450
- arXiv.org > astro-ph > arXiv:1910.03485 > 08 Oct 2019
