Nanometre-scale infrared chemical imaging of organic matter in ultra-carbonaceous Antarctic micrometeorites (UCAMMs)

Aims. The composition of comets and asteroids sheds light on the formation and early evolution of the solar system. The study of micrometeorites containing large concentrations of carbonaceous material (i.e. ultra-carbonaceous antarctic micrometeorites, UCAMMs) allows for unique information on the association of minerals and organics at surface of icy objects (comets) to be obtained.Methods. In this work we map the organic matter of UCAMMs collected in the Antarctic snow, at sub-wavelength spatial scales using the Atomic Force Microscope InfraRed (AFMIR) technique. The sample preparation did not involve any chemical pretreatment to extract organic matter. The AFMIR measurements were performed on a limited spectral coverage (1900–1350 cm−1 ) allowing chemical functional groups to be imaged at spatial scales relevant to the study of micrometeorites.Results. The AFMIR images reveal the variability of the functional groups at very small scales and the intimate association of carbon- and oxygen-bearing chemical bonds. We demonstrate the possibility to potentially separate the olefinic and aromatic C=C bonding in the subcomponents of the UCAMM fragment. These variations probably originate in the early mixing of the different reservoirs of organic matter constituting these dust particles. The measurements demonstrate the potential for analysing such complex organic-matter – mineral association at scales below the diffraction limit. The development of such studies and extension to the full infrared range spectral coverage will drive a new view on the vibrational infrared analysis of interplanetary material.