The Tagish Lake Meteorite: Clues to the Maturation of Organic Matter in the Early Solar System

Transcription

1 The Tagish Lake Meteorite: Clues to the Maturation of Organic Matter in the Early Solar System Chris Herd Earth and Atmospheric Sciences Institute for Space Science, Exploration and Technology University of Alberta

2 Meteorites Meteorites and Other Astromaterials Asteroids Moon Mars Lunar samples Apollo Luna IDPs Sample Return Stardust Genesis Hayabusa Image credit: Widdowson (2004)

3 8:43 AM January 18, 2000 Artist s digital rendition on photo of landscape Hildebrand et al. (2006)

4 Carbonaceous chondrites Allende 1 mm The Solar Ga 1 mm

5 Organics in carbonaceous chondrites Extractable compounds of C, H, O, N and S < 25% soluble organic matter (SOM) > 75% insoluble organic matter (IOM), kerogen-like Similar to what is seen in space Cepheus B

6 The Tagish Lake Meteorite Image of Sample 2 courtesy of Ian Nicklin, Royal Ontario Museum Ungrouped carbonaceous chondrite Affinities to CI and CM Most C-rich chondrite nearly 6 wt% total C 3 wt% organic C Contains various organic species, including amino acids (Pizzarello et al., 2001)

7 Tagish Lake IOM: Previous Work Alexander et al. (2007) Cody and Alexander (2005)

8 The Tagish Lake Meteorite Sample 1; 159 g, ~10 cm in longest dimension Pristine specimens: Approx. 860 g collected days after the fall Minimal contamination, frozen Acquired in 2006 Michael Holly, Creative Services, University of Alberta Hildebrand et al. (2006)

9 Organic Matter in Carbonaceous Chondrites Observations - I: Enrichments in heavy stable isotopes (H, N, C) for a number of compounds Used as a telltale for extraterrestrial origin δd > +100, δ 15 N > +60, δ 13 C ~ -20 to +45 Structural diversity Branched-chain isomers Decrease in concentration with increasing carbon number Any enantiomeric excesses are L-excesses Life uses L-enantiomer (amino acids) Assumption: racemic mixtures are primary

10 Organic Matter in Carbonaceous Chondrites Observations - II: IOM is heterogeneous on a nanoscale D and 15 N-enriched nanoglobules Organic matter closely associated with lowtemperature minerals (matrix, esp. clays) Nakamura-Messenger et al. (2006)

11 Prebiotic Molecules in Carbonaceous Chondrites Amino Acids Amino Acids Sugars Fatty acids

12 Fatty/Carboxylic Acids 1 Formic acid Insect stings 2 Acetic acid Vinegar 4 Butyric acid Rancid butter 10 Capric acid

13 Phosphatidylcholine (a phospholipid) Main structural component of cell membranes

14 A Typical Cell Membrane Phospholipids self-assemble into a spherical bilayer

15 Organic Matter in Meteorites: Mechanisms Problem: multiple pathways to make the same compound In contrast to mineral assemblages, for which petrological analysis can differentiate primary minerals from aqueous-alteration products, methods are not established for identifying primary and secondary organic compounds in meteorites. Shock and Schulte (1990) Solutions (?): compound-specific stable isotopes; petrologic context

16 Organic Matter in Meteorites: Mechanisms Interstellar/nebular (cold space) Supported by high Deuterium contents, nanoglobules Parent body (asteroid) aqueous alteration Supported by mineralogy and petrology

17 What are the relative roles of interstellar, nebular, and parent body processes in the formation of organic molecules? Mineralogy and petrology reflect geologic processes Do differences in the type, amount, and composition of organic matter correlate with lithological differences?

18 Tagish Lake not all pieces are alike Sample 11i dark, dusty Sample 11h Sample 2 1 cm 1 cm Sample 11v disaggregated (collected and stored in Ziploc bag) Compact, coherent fragments 1 cm Sample 5b compact, coherent

19 Samples Sample 11i dark, dusty Preserved 1 cm SEM, TEM, EPMA Sample 2 Subsampling done with sterile scalpels in a walk-in freezer Soluble organic extraction (DCM, H2O) IOM analysis NanoSIMS Bulk 1 cm Sample 5b compact, coherent Compact, coherent fragments

20 Lithological Differences 5b Mineralogically very similar; petrologically different Indicators of aqueous alteration increase in the order 5b 11h 11i 11v is a breccia 11i 200 µm 1000 µm

21 Insoluble Organic Matter Herd et al. (2011)

22 Tagish Lake in situ IOM Raster ion images of IOM separates 5b D/H D/H v m m Herd et al. (2011)

23 Tagish Lake IOM Best explanation: Aqueous alteration on Tagish Lake parent body Reduces D, destroys nanoglobules, increases aromatic character Herd et al. (2011)

24 Tagish Lake IOM Analogous to terrestrial kerogens After Alexander et al. (2007)

25 Tagish Lake Soluble Organic Matter If hydrothermal alteration goes as 5b < 11h < 11i, do the soluble organics follow? Monocarboxylic acids (MCAs) Longer-chain homologues are fatty acids, components in cell walls Amino acids Building blocks of proteins Other (not discussed here)

26 δ 13 C ( ) MCAs: δ 13 C vs Carbon number If 5b 11h 11i Carbonates δ 13 C h 11v 11i 5b Murchison 0-10 acetic formic Mostly flushed out Carbon number From alteration of IOM

27 Mechanisms for MCA modification Trends indicate role of parent body processing Production of MCAs from IOM C (e.g., 5b) MCAs generated from oxidized Murchison IOM (Huang et al. 2007; Oba and Naraoka, 2006) Exchange of carboxyl C with inorganic C (e.g., 11h); with carbonate (+67 )? Insights from terrestrial oil-prone source rocks Overall loss (e.g., 11v, 11i)

28 Amino Acids If 5b 11h 11i After Glavin et al. (2010)

29 Amino Acids

30 L-Isovaline Excesses and b-alanine/glycine Ratios If 5b 11h 11i 11i 5b 11h Secondary pulse of glycine, racemic isovaline? After Herd et al. (2011)

31 Putting the pieces in order: Sample 11h Sample 11i Sample 5b (Sample 11v) 1 cm Sample 2 Preservation of nanoglobules, D- rich IOM MCAs from IOM L-excess amino acids Compact, coherent fragments 1 cm Modification/removal of nanoglobules, D- depletion of IOM Exchange of MCAs with carbonate Secondary amino acid production 1 cm More alteration by water Destruction of nanoglobules, further D-depletion of IOM, increasing aromatic character Loss of MCAs Loss of amino acids

32 Asteroid Hydrogeology After Young et al. (2003)

33 Delivery of prebiotic molecules to the early Earth

34 ISM/Outer Solar System formation The Big Picture Meteorite parent bodies Early Earth Hydrothermal processing (destruction or synthesis) LIFE

35 Sasha Blinova and Danielle Simkus Earth and Atmospheric Sciences Don Morgan Chemistry University of Alberta Robert Hilts and Aaron Skelhorne MacEwan University Collaborators Larry Nittler, Conel Alexander, George Cody, Yoko Kebukawa, Frank Gyngard Carnegie Institution of Washington Greg Slater, Jenny Kirby McMaster University Rhonda Stroud, Brad De Gregorio Naval Research Laboratory Science, 10 June 2011 (v. 332, ) Yongsong Huang, Rafael Tarozo Brown University Zach Sharp University of New Mexico Daniel Glavin, Michael Callahan, Jason Dworkin, Jamie Elsila NASA GSFC

36 Subzero Facility for Curation and Handling of Planetary Materials Unique facility Ar glove box within a -20 C environmental chamber Enables astromaterials processing under cold, clean conditions Class 1000 clean anteroom, with door to environmental chamber (at left)

37 Subzero Facility for Curation and Handling of Planetary Materials Prevents against: Volatile loss Atmospheric oxidation Terrestrial metabolism Ar glove box in freezer

38 Future work Processing of specimens under cold, inert conditions In situ analysis of interior surfaces Best practices for sample return Applications to other meteorite types, especially fresh falls Sample 1; 159 g, ~10 cm in longest dimension

39 This just in Fell July 18, 2011 > 15 kg recovered starting October First Martian meteorite fall since g specimen of the Tissint martian meteorite (University of Alberta Meteorite Collection)

40