STRUCTURE AND BONDING OF PRIMITIVE ORGANIC MATTER IN CARBONACEOUS CHONDRITE METEORITES AND COMET 81P/WILD 2 PARTICLES COLLECTED BY STARDUST

Organic matter is present in several extraterrestrial materials, including carbonaceous chondrite meteorites, interplanetary dust particles, and cometary material collected by the Stardust mission. The most primitive of these materials contain presolar organic matter, identified by extreme enrichments of hydrogen and nitrogen isotopes relative to terrestrial and solar values. However, the origin, molecular structure, and degree of secondary alteration of this unprocessed, primitive organic matter (POM) are largely unknown. Robust characterization of the structure and bonding of POM in primitive extraterrestrial materials will provide insight into presolar and interstellar organic chemistry, as well as processes of initial solar system formation. Moreover, since delivery of extraterrestrial organic matter by meteorites, interplanetary dust, and comets onto the early Earth may have played a vital role in the emergence of living organisms, determining the nature of POM is important for understanding the building blocks of early life and potential prediction of life elsewhere in the universe.

We will present results of transmission electron microscopy (TEM) and scanning transmission x-ray microscopy (STXM) on select chondrite and cometary samples containing POM. Primitive “hotspots” are first identified by hydrogen and nitrogen isotopic mapping with secondary ion mass spectrometry. These hotspots are then extracted using a focused ion beam scanning electron microscope (FIB-SEM), which uses a Ga⁺ ion beam to excavate material on either side of a region of interest, resulting in thin sections transparent to electrons or x-rays. Molecular structure can be determined from correlated electron energy-loss near-edge structure spectroscopy (ELNES) in the TEM and x-ray absorption near-edge structure spectroscopy (XANES) in the STXM. ELNES and XANES are used to detect the relative abundance of aromatic and aliphatic carbon bonds and the presence of organic functional groups, such as carbonyl or nitrile.