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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - Photonis (Isotope Fractionation of Light Elements Upon Ionization: Cosmochemical and Geochemical Implications)

Teaser

Summary

Volatile elements such as hydrogen, nitrogen and noble gases present large isotope variations among solar system objects and reservoirs (including planetary atmospheres) that remain unexplained at present. Works based on theoretical approaches are model-dependent and do not reach a consensus. Laboratory experiments are required in order to develop the underlying physical mechanisms.

The aim of the project is to investigate the origins of and processes responsible for isotope variations of the light elements and noble gases in the Solar System through an experimental approach involving ionization of gaseous species. We investigate the significant isotope variations observed for noble gases and stable isotopes among solar system objects and reservoirs, which are presently debated between a pre-solar origin (ion-molecule interactions, or nucleosynthetic anomalies) and protosolar nebula processing. We target the second possibility by carrying out new experiments. There were three tasks:
Task 1: Synthesis of solid organic compounds by microwave plasma ionization of gas in the laboratory.
Task 2: Synthesis of gaseous and solid organics by photon ionization/dissociation of gas mixtures in a VUV cell coupled to the DESIRS line, Soleil synchrotron.
Task 3: Gas-ice interactions: fractionation of noble gases and stable isotopes. This task was designed to investigate the origin and processing of volatile elements in cometary ice, for which new constraints arose from the analysis of the coma of Comet 67P/Churyumov-Gerasimenko.

The project is to investigate the sources of volatile elements in the solar system and processes that fractionated their isotopic compositions. Doing so, we aim at understanding processes that led to the genesis of organic matter in the solar system, as well as to the the development and processing of planetary atmospheres, a long debated subject which is relevant to the origin of environmental conditions necessary for the development of life on Earth.

Work performed

\"Task 1: Synthesis of solid organic compounds by microwave plasma ionization of gas.

We have developed a new system; called \"\"Nebulotron\"\" consisting of a high vacuum glass line in which adjustable gas mixtures can be flowed through a microwave (2.45 GHz) plasma discharge. The system was implemented from a previous generation, by adapting it to high vacuum, precluding the use of any organic joint. The system has been built and the first analyses were carried out during the first year of the project. The flown gases were mixtures of H2, CO, N2 and noble gases. We succeeded in producing organics. We carried out a series of analyses dedicated to investigate the molecular structure (gas chromatography-mass spectrometry, 13C-nuclear magnetic resonance spectroscopy, Fourier transformed infrared spectroscopy) and isotopic composition (NanoSIMS) of H and N in Nebulotron products (collaboration with the laboratory of Sylvie Derenne, Univ. Paris 6). We have coinjointly carried out a modeling approach in which the results were integrated in a global model of organic matter generaton and transport in the nascent solar system, in collaboration with Dr. SÃ©bastien Charnoz (IPGP) (Bekaert et al, 2018).

Task 2: Synthesis of gaseous and solid organics by photon ionization/dissociation of gas mixtures in a VUV cell coupled to the DESIRS line, Soleil synchrotron.

We are investigating the effect of photo-irradiation on the isotope composition of organic products formed in the context of the protoplanetary disk. Using the high flux of the DESIRS UV-photon line, we expect to form and trap the organic products of the irradiation of simple gas mixtures (N2:CH4 and H2:N2:CO) to measure their chemical and isotopic composition at CRPG and compare them to extraterrestrial organic materials. Unfortunately and contrary to our expectation, we have been awarded only 5 days of beam time on DESIRS but have applied for additional time. During these 5 days, we observed the formation of organic products with the QMS (notably HCN and C2H2). The condensable gas products were collected with cold traps during or after the experiments. The released of the mixture in the evacuated chamber after two experiments was performed to characterise the molecular composition with the QMS. We observed the production and trapping of C2- and C3-hydrocarbons as well as HCN molecules. No solid product was observed nor collected during these experiments. Five cold traps were brought back to CRPG for further analyses of their chemical and isotopic composition using mass spectrometers with a higher sensitivity than the QMS used for the analyses. we also carried out original experiments of photo-ionization using the APSIS setup at LATMOS laboratory to provide experimental insights into pathways of photochemistry-driven molecular growth within outer Circum-Stellar Envelopes (CSE). EUV photons mimicking the interstellar UV field were generated by using a neon gas-discharge type VUV lamp coupled windowless to the photochemical APSIS reactor (Tigrine et al. 2016).

Task 3: Gas-ice interactions: fractionation of noble gases and stable isotopes.

The idea was to study the fractionation of noble gas and stable isotopes upon trapping in ice, and irradiation of ice. Originally, we planned to do the experiments in the laboratory of Dr. Murthy Gudipati (JPL). we investigated the ionization dynamics of Xe atoms interacting with water ice using the recently developed Resonant Two- Step Laser Ablation Mass Spectrometry (2S-LAI-MS). Due to inherent difficulties of the installation for our application (see the Problems and Difficulties section), we decided to develop at CRPG Nancy a new system ada pted to our research goals. The EXCITING (Exploring Xenon in Cometary Ice by Trapping and Irradiating Noble Gases) experimental set-up has been successfully built in our laboratory. It allows water-noble gas mixtures to be flown and adjusted using a quadrupole mass spectrometer, before being condensed onto\"

Final results

We develop the production of organic matter upon irradiation of gas mixtures. In particular, we aim at using photons to do so, which is a world premiere.
We develop two original systems: a new high vacuum ionization line, and a new ice irradiation experiment. With the latter, we are able to analyse directly noble gas and stable isotope compositions with online analyzers.
We use the latest analytical techniques to characterize the elemental, molecular, and isotopic compositions of synthesized organics using an large array of methods including ion probe, noble gas, stable isotope and state of the art organic analyses.
At the end of the project, we expect to be able to decipher the origin of organic matter in the solar system. We also develop a modeling approach for transport of organics in the solar system, which is fed with our experimental results. Such an approach has never be attempted before.