The analysis of organic matter at the size scale of individual inclusions shown in Fig. 3 was difficult and similar to the challenges posed by interplanetary dust particles and returned Comet 81P/Wild2 samples/particles, for example. The most powerful tools for such analyses are STXMs (soft) or scanning transmission x-ray spectrometers. STXMs use Fresnel zone plate optics, providing a theoretical spot size of 30 nm; in optimum cases, smaller structures (approximately 15 nm) can be resolved. In the present case, the STXM located at beamline 5.3.2 at the Advanced Light Source, Lawrence Berkeley Laboratory, was used for all analyses. The maximum scanning rates for the STXM at beamline 5.3.2 is 12 Hz, with a scanning range of 4000 pixels by 2000 pixels, covering a region up to 20 mm by 4 mm, with a minimum step size of 2.5 nm. Sample position precision during spectra acquisition was better than 50 nm (controlled by laser interferometery). C-, N-, and O-XANES (x-ray absorption near-edge structure spectroscopy) spectra were acquired using a multispectral imaging method. The “stacks” method relied on creating a highly aligned hyperspectral data cube of x by y pixelated images acquired over a range of energies that span a given XANES region. In the fine structure regions of the near edge, the energy step size (ΔE) typically used was 0.1 eV; in the less featured pre- and post-edge regions, energy steps of 1 to 2 eV were sufficient for spectral resolution. C-XANES reveals the presence and abundance of various organic functional groups via the detection of characteristic absorption features in the near-edge (preionization) region of the x-ray absorption spectrum. In general, absorption at the lowest energies (approximately 285.0 eV) is well described by photoexcitation of carbon 1s electrons to low-energy, unoccupied, π0 orbitals of alkenyl and aromatic species (C and H substituted). Carbon substitution with more electronegative atoms (e.g., N and O) results in shifts to higher excitation energies, e.g., 288.5 eV in the case of carboxyl 1s-π0 transitions.

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