title: Organic globules in the Tagish Lake meteorite: remnants of the protosolar disk.
abstract: Coordinated transmission electron microscopy and isotopic measurements of organic globules in the Tagish Lake meteorite shows that they have elevated ratios of nitrogen-15 to nitrogen-14 (1.2 to 2 times terrestrial) and of deuterium to hydrogen (2.5 to 9 times terrestrial). These isotopic anomalies are indicative of mass fractionation during chemical reactions at extremely low temperatures (10 to 20 kelvin), characteristic of cold molecular clouds and the outer protosolar disk. The globules probably originated as organic ice coatings on preexisting grains that were photochemically processed into refractory organic matter. The globules resemble cometary carbon, hydrogen, oxygen, and nitrogen (CHON) particles, suggesting that such grains were important constituents of the solar system starting materials.
authors.affiliation: Robert M. Walker Laboratory for Space Science, Astromaterials Research and Exploration Science Directorate, NASA Johnson Space Center, Houston, TX 77058, USA. keiko.nakamura-1@nasa.gov
authors.forename: Keiko
authors.initials: K
authors.lastname: Nakamura-Messenger
authors.forename: Scott
authors.initials: S
authors.lastname: Messenger
authors.forename: Lindsay P
authors.initials: LP
authors.lastname: Keller
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Clemett
authors.forename: Michael E
authors.initials: ME
authors.lastname: Zolensky
mesh_terms: D002244:Carbon / Q000032:analysis*; D002247:Carbon Isotopes / Q000032:analysis; D003903:Deuterium / Q000032:analysis; D006859:Hydrogen / Q000032:analysis*; D007053:Ice; D019110:Meteoroids; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D010100:Oxygen / Q000032:analysis; D013696:Temperature; D014466:Ultraviolet Rays
chemical_list: D002247:Carbon Isotopes; D007053:Ice; D009587:Nitrogen Isotopes; D002244:Carbon; D006859:Hydrogen; D003903:Deuterium; D009584:Nitrogen; D010100:Oxygen