Meteorite studies suggest that each solar system object has a unique oxygen isotopic composition. Chondrites, the most primitive of meteorites, have been believed to be derived from asteroids, but oxygen isotopic compositions of asteroids themselves have not been established. We measured, using secondary ion mass spectrometry, oxygen isotopic compositions of rock particles from asteroid 25143 Itokawa returned by the Hayabusa spacecraft. Compositions of the particles are depleted in (16)O relative to terrestrial materials and indicate that Itokawa, an S-type asteroid, is one of the sources of the LL or L group of equilibrated ordinary chondrites. This is a direct oxygen-isotope link between chondrites and their parent asteroid.

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The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

39A comprehensive study of organic chemistry and mineralogy of an ultracarbonaceous 40 micrometeorite (UCAMM D05IB80), collected from near the Dome Fuji Station, Antarctica, 41 has been carried out in order to understand the genetic relationship among organic materials, 42 silicates, and water. The micrometeorite is composed of a dense aggregate of ~5-µm-sized 43 hollow ellipsoidal organic material containing submicrometer-sized phases such as GEMS 44 and mineral grains. There is a wide area of organic material (~15 x 15 μm) in its interior. 45Low-Ca pyroxene is much more abundant than olivine and shows various Mg/(Mg+Fe) ratios 46 from ~1.0 to 0.78, which is common to previous works of UCAMM. By contrast, GEMS 47 amide. The ratio of nitrogen to carbon (N/C) in the smooth region of the organics is ~0.15, 53 which is five times higher than insoluble organic macromolecules in types 1 and 2 chondritic 54 meteorites. In addition, the UCAMM organics is soluble in epoxy, and thus it has 55 hydrophilicity. These polar natures indicate that the organic material in the UCAMM is very 56 primitive. The surface of the organics is coated with an inorganic layer with a few nanometers 57 thickness, which consists of C, O, Si, S, and Fe. Sulfur is also contained in the interior, 58implying the presence of organosulfur moieties. There is no isotopic anomaly of D, 13 C and 59 15 N in the organic material. 60Since interstellar photochemistry alone would not be able to explain the N/C ratio of the 61 UCAMM organics, we suggest that very small amount of fluid on a comet must have been 62 necessary for the formation of UCAMM. The GEMS grains depleted in Mg and S in the 63 UCAMM prove a very weak degree of aqueous alteration, which is weaker than that of 64 carbonaceous chondrites. Short-duration weak alteration probably caused by planetesimal 65 shock locally melts cometary ice grains and releases water that dissolves organics, while the 66 fluid unlikely mobilizes because of very low thermal conductivity of the porous icy body. 67 This event allows formation of a large organic puddle of the UCAMM, as well as organic 68 matter sulfurization, formation of mineral membrane-like thin layers, and deformation of 69 5 organic nanoglobules. 70 (408 words (max. 500 words)) 71 72 9 124 2. Experimental 125 The Antarctic snow, collected by the 51st JARE team of the National Institute of Polar 126 Research (NIPR), was melted and filtered in a class 1000 clean room at Ibaraki University, 127 and the residual particles were manually picked up under a binocular microscope. Details of 128 the micrometeorite collecting method are described by Sakamoto et al. (2010). They were 129 observed with JEOL JSM-5600LV scanning electron microscope (SEM) equipped with 130 energy dispersive spectrometer (EDS) at Ibaraki University and micrometeorites were 131selected from terrestrial materials based on the morphology and EDS spectra with chondritic 132 composition rich in Si, Mg, Fe, and O (see electronic supplementary data, S1). About 90 133 micrometeorites ...

The compound distribution suggests a different source for each compound series or a chromatographic separation effect associated with fluid movement in the meteorite parent body. The DESI-HRMS imaging will further our understanding of organic compound distribution with respect to mineral and water interactions in meteorites.

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ZnO spherical powder with hierarchical structure was synthesized from zinc acetate anhydride and hexamethylenetetramine in a solvent of water and ethylene glycol (EG), and its time evolution was investigated by microscopic and isotope tracer studies. Initially, spherical ZnO particles made of nanocrystallites were precipitated. From the early growth stage, crystallites were radially aligned along the c-axis. With aging, the nanoparticles transformed into hexagonal prism-like particles with pyramidal tops, which showed clear radial alignment. Subsequently, the ZnO spheres became cracked and broke into wedge-shaped pieces of the pyramid-like particles. The microscopic studies suggested that the spherical particles grew through oriented attachment of small particles during the early growth stage, while Ostwald ripening through dissolution−recrystallization changed the component particles to a pyramidal shape in the later stage. In order to investigate the growth process, we attempted a novel isotope tracer study, where H 2 18 O was used for the solvent and the distribution of 18 O in the spherical particles was analyzed by a secondary ion mass spectrometer. The concentric 18 O distribution in the ZnO spherical powder aided the mechanism of continuous concentric-oriented attachment of nanoparticles to form spherical ZnO particles. The difference in the 18 O distribution before and after transformation into the pyramid shape was small, which implies that this change was a local reaction. The oxygen isotope tracer study in water−EG solvent was proven effective in determining the history of the particles and the development of their inner structures.