¹Evan Groopman, ¹Ernst Zinner, ¹Sachiko Amari, ¹Frank Gyngard, ²Peter Hoppe, ³Manavi Jadhav, ⁴Yangting Lin, ⁴Yuchen Xu, ⁵Kuljeet Marhas, ⁶Larry R. Nittler
¹Laboratory for Space Sciences, Physics Department, Washington University, One Brookings Drive, Campus Box 1105, Saint Louis, MO 63130, USA
²Max Planck Institute for Chemistry, Particle Chemistry Department, P.O. Box 3060, D-55020 Mainz, Germany
³Department of the Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA
⁴Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
⁵Planetary Sciences Division, Physical Research Laboratory, Ahmedabad, Gujarat, 380009 India
⁶Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA

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Reference
Groopman E, Zinner E, Amari S, Gyngard F, Hoppe P, Jadhav M, Lin Y, Xu Y, Marhas K, Nittler LR (2015) Inferred Initial 26Al/27Al Ratios in Presolar Stardust Grains from Supernovae are Higher than Previously Estimated.
Astrophyical Journal 803, 31.
Link to Article [doi:10.1088/0004-637X/809/1/31]

^1,2Alyssa K. Cobb, ^1,2Ralph E. Pudritz, ^1,2Ben K. D. Pearce
¹Origins Institute, McMaster University, ABB 241, 1280 Main Street, Hamilton, ON L8S 4M1, Canada
²Department of Physics and Astronomy, McMaster University, ABB 241, 1280 Main Street, Hamilton, ON L8S 4M1, Canada

Carbonaceous chondrite meteorites are known for having high water and organic material contents, including amino acids. Here we address the origin of amino acids in the warm interiors of their parent bodies (planetesimals) within a few million years of their formation, and we connect this with the astrochemistry of their natal protostellar disks. We compute both the total amino acid abundance pattern and the relative frequencies of amino acids within the CM2 (e.g., Murchison) and CR2 chondrite subclasses based on Strecker reactions within these bodies. We match the relative frequencies to well within an order of magnitude among both CM2 and CR2 meteorites for parent body temperatures <200°C. These temperatures agree with 3D models of young planetesimal interiors. We find theoretical abundances of approximately 7 × 105 parts per billion, which is in agreement with the average observed abundance in CR2 meteorites of (4 ± 7) × 105, but an order of magnitude higher than the average observed abundance in CM2 meteorites of (2 ± 2) × 104. We find that the production of hydroxy acids could be favored over the production of amino acids within certain meteorite parent bodies (e.g., CI1, CM2) but not others (e.g., CR2). This could be due to the relatively lower NH3 abundances within CI1 and CM2 meteorite parent bodies, which leads to less amino acid synthesis. We also find that the water content in planetesimals is likely to be the main cause of variance between carbonaceous chondrites of the same subclass. We propose that amino acid abundances are primarily dependent on the ammonia and water content of planetesimals that are formed in chemically distinct regions within their natal protostellar disks.

Reference
Cobb AK, Pudritz RE, Pearce BKD (2015) Nature’s Starships. II. Simulating the Synthesis of Amino Acids in Meteorite Parent Bodies. Astrophysical Journal 809, 6.

Link to Article [doi:10.1088/0004-637X/809/1/6]

¹Thomas J. Zega, ^2,3Pierre Haenecour, ²Christine Floss, ⁴Rhonda M. Stroud
¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721-0092, USA
²Laboratory for Space Sciences and Physics Department, Washington University, One Brookings Drive, Campus Box 1105, St. Louis, MO 63130, USA
³Department of Earth and Planetary Sciences, Washington University, One Brookings Drive, Campus Box 1169, St. Louis, MO 63130, USA
⁴Materials Science and Technology Division, Code 6366, Naval Research Laboratory, 4555 Overlook Ave, SW Washington, DC 20375, USA

We report the first microstructural confirmation of circumstellar magnetite, identified in a petrographic thin section of the LaPaz Icefield 031117 CO3.0 chondrite. The O-isotopic composition of the grain indicates an origin in a low-mass (~2.2 M⊙), approximately solar metallicity red/asymptotic giant branch (RGB/AGB) star undergoing first dredge-up. The magnetite is a single crystal measuring 750 × 670 nm, is free of defects, and is stoichiometric Fe3O4. We hypothesize that the magnetite formed via oxidation of previously condensed Fe dust within the circumstellar envelope of its progenitor star. Using an empirically derived rate constant for this reaction, we calculate that such oxidation could have occurred over timescales ranging from approximately ~9000–500,000 years. This timescale is within the lifetime of estimates for dust condensation within RGB/AGB stars.

Reference
Zega TJ, Haenecour P, Floss C, Stroud RM (2015) Circumstellar Magnetite from the LAP 031117 CO3.0 Chondrite. Astrophysical Journal 808 55.
Link to Article [doi:10.1088/0004-637X/808/1/55]