Quantitative organic and light‐element analysis of comet 81P/Wild 2 particles using C‐, N‐, and O‐μ‐XANES

Abstract

INTRODUCTIONThe Stardust comet sample return mission from comet 81P/Wild 2 provides an unprecedented opportunity to assess the organic chemistry of what may be the most primitive solar system material, providing a link to the molecular cloud material that was the ultimate source of the matter from which our solar system originated. Prior to the Stardust mission, our understanding of the early history of the solar system, in terms of extraterrestrial organic carbon, has been restricted to the analysis of chondrites and interplanetary dust particles (IDPs). In the case of the former, it is clearly evident that the parent body accretion and subsequent alteration has altered the organic matter to an unknown extent from its most primitive origins (e.g., Cody and Alexander 2005;Alexander et al. 2007). In the case of IDPs, thermal processing due to atmospheric entry heating may also transform labile organic matter . In the case of the Stardust mission to comet 81P/Wild 2, sample capture was designed to be as benign as possible given the constraints imposed on Discovery-class missions . Silica aerogel, with a density of 5 to 50 mg/cm 3 , provides a means of Abstract-Synchrotron-based soft X-ray micro-analysis was performed on particles extracted from the Stardust aerogel collector in order to obtain detailed organic functional group information on any organic solids captured as part of the Principal Examination suite of analyses for samples from comet 81P/Wild 2. It is observed that cometary organic carbon captured in aerogel is present in a number of different manifestations and often intimately associated with silicates. Carbon X-ray absorption near edge structure (XANES) spectra reveal considerable chemical complexity in all of the organic particles studied so far. Universally, the comet 81P/Wild 2 organic particles contain low concentrations of aromatic and/or olefinic carbon relative to aliphatic and heteroatom-containing functional groups, e.g., amide, carboxyl, and alcohol/ethers. N-XANES confirms the presence and assignments of these functional groups. In general, the XANES data record considerable chemical complexity across the range of organic samples currently analyzed. The atomic ratios, N/C and O/C, derived from XANES data reveal a wide range in heteroatom content; in all cases these elemental ratios are higher than that of primitive meteoritic organic matter. The wide range in chemistry, both in elemental abundances and specific organic functional groups, suggests that the comet 81P/Wild 2 organic solids may have multiple origins. Quantitative organic and light-element analysis of comet 81P/Wild 2 particles using C-, N-, and O-μ-XANES

Hayabusa2: Scientific importance of samples returned from C-type near-Earth asteroid (162173) 1999 JU3

“…The presence of sulfides formed by aqueous alteration processes (Berger et al, 2011) indicates either aqueous activity on comet Wild 2 or delivery of inner solar-system sulfides to the comet-forming region before comet formation. Organic materials recovered from the Stardust samples were enriched in nitrogen and had more fragile molecular structures compared to those of carbonaceous chondrites, suggesting that they had not been heavily processed and remained frozen in the comet Cody et al, 2008). These new findings have stimulated discussion on material circulation in the proto-solar disk (e.g., Ciesla, 2007).…”

Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites

“…EELS C-K (left column) and N-K edges (right column) of Maribo, Jbilet Winselwan (L#1 = mx1, L#2 = mx2) and Bells, all normalized to total carbon (320 eV) and nitrogen (430 eV). Peak positions are from Cody et al (2008), where in the p à transition (1) $285 eV is associated with aromatic or olefinic carbon (C@C); (2) $286.5 eV is associated with carbonyl/ester (C@O) and ether groups, (CAO) in aldehydes and ketones, as well as nitrile bonding (C"N) environments; (3) $287.5 eV corresponds to aliphatic carbon; (4) $288.5 eV is associated with carbonyl groups in carboxyl moieties (COOH) and (5) $291 eV corresponds to CAC bonding environments in graphene carbon ring structures. Peaks in the N-K edges correspond to: (1) $400 eV nitrile functional groups (C"N); (2) The broader peaks between $403-407 eV belong to amine functional groups in imidazole and pyrrole and the broad peak starting at $411 eV is related to amine functional groups in imidazole.…”

Tanpopo: Astrobiology Exposure and Micrometeoroid Capture Experiments— Proposed Experiments at the Exposure Facility of ISS-JEM

“…Complex organic compounds were also found in comets by the direct analysis of the dust from Comet Halley with mass spectrometer on spacecraft 17) . Ground-based chemical analyses of cometary dust particles returned by Stardust mission have revealed more details of organic chemistry of Comet 81P/Wild 2 18,[30][31][32][33][34] .…”

“…As a subtheme of Tanpopo project, we propose to collect IDPs at low Earth orbit, which will avoid the sample damage due to atmospheric entry heating and the terrestrial contamination. The IDPs will be collected using low-density silica aerogel (0.01 g/cc) 31) . In a ground-based experiment capturing hypervelocity carbonaceous chondrite with aerogel, it has been demonstrated that organic carbon survived in the meteorite samples with only a partial modification after the impact with the velocity of 4 km/s 36) .…”