Formation of an ultracarbonaceous Antarctic micrometeorite through minimal aqueous alteration in a small porous icy body

Abstract

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 ...

Evolution of interstellar organic compounds under asteroidal hydrothermal conditions

“…Although the chondritic IOM contains pyrrole and alkylpyridine groups ( Pizzarello and Williams, 2012;Remusat et al, 2005b ), it is not as N-rich as the IOM that forms in the present experiments (C 100 H 60-80 O 16-18 N 3 S 2-7 ( Derenne and Robert, 2010 ) vs C 100 H 120 O 31 N 30 ). In fact, in terms of N/C and XANES signatures, the insoluble organic products of the present experiments are closer to organic materials of ultracarbonaceous micrometeorites (UCAMM -N/C of ∼0.15-0.2 - Dartois et al, 2013;Yabuta et al, 2017 ). Yabuta et al (2017) have recently interpreted the N-rich organic compounds from one UCAMM as products of incipient aqueous alteration reactions that likely occurred within water coming from locally melted cometary ice grains.…”

“…While the impact of hydrothermal processes on mineral phases has been well identified and constrained (e.g. formation of phyllosilicates, carbonates and sulfides), it remains a subject of investigations for OM ( Alexander et al, 2014Burton et al, 2012;Cody et al, 2011;Cody and Alexander, 2005;Glavin et al, 2010;Martins and Sephton, 2009;Orthous-Daunay et al, 2013;Remusat et al, 2010;Vinogradoff et al, 2017;Yabuta et al, 2017 ). The present study aims at experimentally constrain the impact of hydrothermal alteration on a molecule that is typically formed in interstellar ice analogs.…”

Dome C ultracarbonaceous Antarctic micrometeorites

“…Several countries are involved in these collecting expeditions (e.g. Nakamura et al 2005;Duprat et al 2007;Taylor et al 2008;van Ginneken et al 2012;Yabuta et al 2012Yabuta et al , 2017. The Concordia/CSNSM collection contains thousands of Antarctic micrometeorites collected near the Frenchsend offprint requests to emmanuel.dartois@u-psud.fr Part of the equipment used in this work has been financed by the French INSU-CNRS program "Physique et Chimie du Milieu Interstellaire" (PCMI).…”

A microchondrule‐bearing micrometeorite and comparison with microchondrules in CM chondrites

“…; Yabuta et al. ) and provide a compelling example of how extraterrestrial dust has expanded our collective inventory of solar system materials. Likewise, unique micrometeorites with asteroidal affinities are also known; these include a fragment of basaltic crust derived from a differentiated protoplanet (Gounelle et al.…”

“…Carbon-rich micrometeorites, characterized by extreme deuterium excesses (Duprat et al 2010), and containing glass with embedded metal sulfides (GEMS) and primitive nebular condensates are currently associated with distant cometary parent bodies, formed beyond the nitrogen snow line (Dartois et al 2013(Dartois et al , 2018. These particles are termed ultracarbonaceous Antarctic micrometeorites (UCAMMs) (Dobricǎ et al 2009;Duprat et al 2010;Imae et al 2013;Noguchi et al 2017;Yabuta et al 2017) and provide a compelling example of how extraterrestrial dust has expanded our collective inventory of solar system materials. Likewise, unique micrometeorites with asteroidal affinities are also known; these include a fragment of basaltic crust derived from a differentiated protoplanet ); a polycrystalline, fine-grained micrometeorite exhibiting evidence of flash heating and quench cooling while in space (Noguchi et al 2013); and an unusually Ni-rich, oxidized, and irradiated giant micrometeorite with possible affinities to the CK chondrite class (Cordier et al 2018).…”