Argon retentivity of carbonaceous materials: feasibility of kerogen as a carrier phase of Q-noble gases in primitive meteorites

Abstract

Extremely large amounts of heavy noble gases are concentrated in phase Q, which seems to be a carbonaceous phase analogous to terrestrial Type III kerogen. Phase Q must have very high noble gas retentivity based on the presence of such extremely large amounts of heavy noble gases in a very minor fraction of the meteorite. To verify that kerogen is a carrier phase of Q-noble gases, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) using synchrotron radiation were carried on for kerogens (coals) and carbon allotropes that had been bombarded by 3-keV Ar ions, and the Ar retentivities of the two materials were compared. This comparison of the estimated Ar concentrations in the target materials revealed that carbon allotropes (graphite, fullerene, carbon nanotube, and diamond) have a much higher Ar retentivity than kerogens. This unexpected result clearly shows that the terrestrial kerogens tested in our study are not suitable as a carrier phase of Ar and, consequently, that phase Q may not be similar to the terrestrial kerogen tested. If heavy noble gases are really concentrated in carbonaceous components of primitive meteorites, phase Q may have a more ordered structure than terrestrial kerogen based on the fact that the greatest difference between terrestrial kerogen and carbon allotropes is the degree of order of the molecular structure.

Exploring Refractory Organics in Extraterrestrial Particles

“…Its disordered structure can be described as a mixture of aromatic and aliphatic subunits containing a large number of functional groups. It is now well accepted that the refractory organic materials in cometary dust as well as in meteorites are dominated by high molecular weight organic components very similar to kerogen-like materials (Osawa et al 2009;Matthewman et al 2013;Wooden et al 2017).…”

Trapped Water on Silicates in the Laboratory and in Astrophysical Environments

“…In order to modify the morphology and structure of the condensed silicates (in particular the grain sizes and porosity), two samples were annealed in a 2 mbar argon atmosphere for three hours at 500°C and 900°C, respectively. It is now well accepted that the refractory organic materials in cometary dust as well as in meteorites are dominated by high-molecular-weight organic components very similar to the kerogen-like material (Osawa et al 2009;Matthewman et al 2013;Wooden et al 2017). The disordered structure of kerogen is not well defined and can be described as a mixture of aromatic and aliphatic subunits containing a large number of functional groups.…”

Quantitative Estimation Methods for Concentrations and Layer Thicknesses of Elements Using Edge-jump Ratios of X-ray absorption spectra

“…A previous work used the edge-jump ratio of Ar K edge on XAS as an index for the concentration of Ar. 1 The amount of atoms implanted in the target material need to be measured using the appropriate type of mass spectrometry to determine its accurate concentration. However, the measurements completely destroy the sample because the sample has to be totally pyrolyzed in an ultra-high vacuum or totally dissolved in acids.…”