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Deuterium Isotope Fractionation of Polycyclic Aromatic Hydrocarbons in Meteorites as an Indicator of Interstellar/Protosolar Processing HistoryThe stable isotope composition of soluble and insoluble organic compounds in carbonaceous chondrites can be used to determine the provenance of organic molecules in space. Deuterium enrichment in meteoritic organics could be a residual signal of synthetic reactions occurring in the cold interstellar medium or an indicator of hydrothermal parent-body reactions. δD values have been measured in grains and bulk samples for a wide range of meteorites; however, these reservoirs are highly variable and may have experienced fractionation during thermal and/or aqueous alteration. Among the plethora of organic compounds in meteorites are polycyclic aromatic hydrocarbons (PAHs), which are stable and abundant in carbonaceous chondrites, and their δD ratio may preserve evidence about their formation environment as well as the influence of parent-body processes. This study tests hypotheses about the potential links between PAHs-deuteration concentrations and their formation conditions by examining the δD ratio of PAHs in three CM carbonaceous chondrites representing an aqueous alteration gradient. We use deuterium enrichments in soluble 2–5-ring PAHs as an indicator of either photon-driven deuteration due to unimolecular photodissociation in warm regions of space, gas-phase ion–molecule reactions in cold interstellar regions of space, or UV photolysis in ices. We also test hypothesized reaction pathways during parent-body processing that differ between partially and fully aromatized PAHs. New methodological approaches were developed to extract small, volatile PAHs without fractionation. Our results suggest that meteoritic PAHs could have formed through reactions in cold regions, with possible overprinting of deuterium enrichment during aqueous parent-body alteration, but the data could not rule out PAH alteration in icy mantles as well.
Document ID
20220012219
Acquisition Source
Goddard Space Flight Center
Document Type
Accepted Manuscript (Version with final changes)
Authors
H V Graham
(Goddard Space Flight Center Greenbelt, Maryland, United States)
J E Elsila ORCID
(Goddard Space Flight Center Greenbelt, Maryland, United States)
J P Dworkin ORCID
(Goddard Space Flight Center Greenbelt, Maryland, United States)
S A Sandford
(Ames Research Center Mountain View, California, United States)
J C Aponte ORCID
(Goddard Space Flight Center Greenbelt, Maryland, United States)
Date Acquired
August 8, 2022
Publication Date
September 1, 2022
Publication Information
Publication: Life
Publisher: MDPI
Issue Publication Date: September 1, 2022
e-ISSN: 2075-1729
Subject Category
Astrophysics
Funding Number(s)
WBS: 811073.02.52.01.04.06
CONTRACT_GRANT: NASA Emerging Worlds Program 16-EW16_2-0046
CONTRACT_GRANT: NASA Emerging Worlds Program 17-EW17_2-0033
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
Technical Review
External Peer Committee
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