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UV Photolysis of Cometary and Planetary Ices in the SubLIME Lab

Presentation #103.04 in the session Unmeltable Me, verse 1: From the Sky to the Lab.

Published onOct 20, 2022
UV Photolysis of Cometary and Planetary Ices in the SubLIME Lab

Ice is prevalent throughout the solar system, from the permanently shadowed depths of Mercurian craters to icy bodies in the far reaches of the Kuiper Belt and beyond. The chemistry of these ices is influenced by several parameters, including the solar UV flux and temperature. Understanding these influences help to uncover how molecular complexity evolves from relatively simple species in the natal molecular cloud to prebiotic molecules that may have been delivered to the early Earth by comets and meteorites. Studying this chemistry also may help to explain the chemical diversity observed in different planetary bodies. Laboratory studies of energetically processed cosmic ice analogues have revealed a large number of chemical formation routes and require sensitive analytical techniques to identify the composition of ice and gas products formed. The unique identification of organic species can be challenging and often requires structure-specific techniques to identify structural isomers, conformers, and isotopologues. The Sublimation Laboratory Ice Millimeter/submillimeter Experiment (SubLIME) explores cometary and planetary ice chemistry with the structure-specificity of rotational spectroscopy to identify and measure the abundance ratios of products sublimated from UV-photolyzed ices. Samples are formed at low temperature (~10 K) and photolyzed at temperatures relevant to planetary bodies. After photolysis, the samples are slowly heated to 300 K to sublimate the volatile products, the gas mixture of which is then analyzed with (sub)millimeter spectroscopy. We present the experimental setup and research projects of SubLIME, including results of UV-photolyzed ice analogues containing water (H2O), carbon monoxide (CO), methanol (CH3OH), and acetonitrile (CH3CN). We discuss previous findings of methanol photolysis, which yielded three newly detected complex organics—ethylene oxide, vinyl alcohol, and ketene—in the sublimated gas mixture (Yocum et al. 2021). Additionally, new work on mixed ices provokes interesting new species not necessarily detectable with other techniques. Experimental results and current projects are discussed in the context of observations of comets and other planetary bodies.

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