Organic matter in carbonaceous chondrites is distributed in fine-grained matrix. To understand pre- and postaccretion history of organic matter and its association with surrounding minerals, microscopic techniques are mandatory. Infrared (IR) spectroscopy is a useful technique, but the spatial resolution of IR is limited to a few micrometers, due to the diffraction limit. In this study, we applied the high spatial resolution IR imaging method to CM2 carbonaceous chondrites Murchison and Bells, which is based on an atomic force microscopy (AFM) with its tip detecting thermal expansion of a sample resulting from absorption of infrared radiation. We confirmed that this technique permits ∼30 nm spatial resolution organic analysis for the meteorite samples. The IR imaging results are consistent with the previously reported association of organic matter and phyllosilicates, but our results are at much higher spatial resolution. This observation of heterogeneous distributions of the functional groups of organic matter revealed its association with minerals at ∼30 nm spatial resolution in meteorite samples by IR spectroscopy.

Supplemental Materialof "Submicron-resolution polymer orientation mapping by optical photothermal infrared spectroscopy" Estimation of spatial resolution of O-PTIR measurementsWe estimated the spatial resolution of our O-PTIR system by measuring the spectral changes across the interface between the biphenol A type epoxy resin and the PET (Fig. S1(a)). A thick cross-sectioned sample with thickness of approximately 10 mm was measured. The peak intensities at 1730 cm −1 for the PET C=O group and 1508 cm −1 for the epoxy benzene ring were measured at a spacing of 50 nm to calculate the ratio of these intensities (I1730/I1508) (Fig. S1(b)). Even if a single peak intensity fluctuates as a result of defocusing caused by a nonhorizontal sample surface, the peak ratio should remain constant. The profile of the peak ratio (I1730/I1508) was then fitted to a sigmoid curve with a constant offset (red line) (Fig. S1(c)). The spatial resolution was estimated to be approximately 800 nm from the full width at half maximum (FWHM) of the first derivative (green line) of the fitted sigmoid curve with respect to the position across the interface.

A water soluble amorphous form of silk was made by ultra-short laser pulse irradiation and detected by nanoscale IR mapping. An optical absorptioninduced nanoscale surface expansion was probed to yield the spectral response of silk at IR molecular fingerprinting wavelengths with a high ∼ 20 nm spatial resolution defined by the tip of the probe. Silk microtomed sections of 1-5 µm in thickness were prepared for nanoscale spectroscopy and a laser was used to induce amorphisation. Comparison of silk absorbance measurements carried out by table-top and synchrotron Fourier transform IR spectroscopy proved that chemical imaging obtained at high spatial resolution and specificity (able to discriminate between amorphous and crystalline silk) is reliably achieved by nanoscale IR. A nanoscale material characterization using synchrotron IR radiation is discussed.

Asteroids and comets are thought to form in the inner and outer solar systems, respectively. Chondritic porous and smooth interplanetary dust particles (CP IDPs and CS IDPs, respectively) in the stratosphere are regarded as dust grains from comets and hydrated asteroids, respectively. Here, we describe an Antarctic micrometeorite (AMM) composed of lithologies of both CP and CS IDPs. In addition to the CS IDP-like compact lithology that experienced severe aqueous alteration, the CP IDP-like porous lithology shows evidence of very weak aqueous alteration. The structure of the organic matter in the porous lithology varies from that in the CP IDPs to aromatic-rich organic matter. In contrast, the structure of the organic matter in the compact lithology is homogenous, which is consistent with higher degrees of aqueous alteration. Its structure is more similar to that of CP IDPs and Wild 2 samples than that of meteoritic insoluble organic matter, suggesting that the compact lithology formed from the porous lithology. Some CP IDPs are related to cometary dust streams, such as those originating from 26P/Grigg-Skjellerup. In addition, the presence of this AMM indicates an additional origin of the CP IDPs and their equivalent AMMs. The mineralogy and organic chemistry of this AMM suggest that its parent body was composed of the same building blocks as those of the comets, and later experienced incomplete aqueous alteration. The AMM probably formed as microbreccia in the regolith layer composed of materials from a CP IDP-like crust and a hydrated interior.

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