The Fine Detail of Comet Wild 2: TEM and Synchrotron Characterisation

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1 The Fine Detail of Comet Wild 2: TEM and Synchrotron Characterisation John Bridges Hitesh Changela Steve Gurman Space Research Centre, Dept. of Physics & Astronomy, University of Leicester, UK JeNAM 29, Bridges et al. Comet Wild2

2 Oxide Minerals in Wild 2 Sample return from short period Comet Wild2, 26- Identify and characterise oxide minerals in Wild2 How common are they in the samples? Capture related oxidation? High temperature e.g. Fe-Cr-V-Ti oxides? Other origins - low temperature hydrothermal, space weathering? Compare this short period comet to chondrites, Interplanetary Dust Particles (IDPs)

3 Samples: Tracks 41, 121, 134 Track 41 type B turnip Track 134 type A carrot Track length 4 mm, slice.8 mm from entrance - No previous analyses Track length.4 mm Track 121 type A carrot - ferric oxide (Hematite) microraman Foster et al. LPSC XXXIX, Mg-silicates Bridges et al. LPSC XXXIX Track length.9 mm

4 Samples: Tracks 41, 121, 134 Track 41 Grossemy et al. 28 predict near entrance samples will show some oxidation 1 mm Track No previous analyses Au Track Terminal area slices on Au mounts Fe-O 5 m Au 5 m

5 Techniques 1: FIB-SEM, TEM 1 m 1 m FIB-SEM extraction of Fe oxide from track 121 material on Au mounts Quanta 2 3D, Omniprobe, 1 nm wafers on Cu grid (Changela & Bridges, LPSC XXXX; Bridges et al. MAPS 29) TEM Jeol 21 LaB 6, 2 kv Selected Area Diffraction, STEM, EDS Microtome sections (NASA- JSC), FIB-SEM sections (U. Leicester) 1 m

6 Techniques 2: Synchrotron 1 cm Diamond Light Source, UK 3 GeV, 2 ma Beamline I18, nine element Ge detector (detect Ca upwards), monochromated, 13 kev range, E/E XANES (& EXAFS) Energy steps.2-.4 ev, ev Mineral standards Fe, hematite, XRS magnetite, goethite, pyrrhotite, olivine 4 m step size, 5s spot analyses 25 m x 25 m maps Sample mount Beamline I18

7 Intensity Track 121 Terminal Area TEM 5 m 5 m Fe-oxide Au M Au Fe M K C Kα STEM EDX α 8 STEM image.2 m EDS Mapping Au Mα Fe Lα O Ga Energy (kev) Energy KeV β No electron diffraction - amorphous JeNAM 29, Bridges et al. Comet Wild2

8 Flux Flux Flux Flux Flux Track 41 slice XRS maps and spectra Ni K similar) 8 m 1 mm 8 m 8.x1 4 6.x1 4 Fe hotspot Fe hotspot 4.x x Cr K Zn K red green blue x1 4 6x1 4 5x1 4 4x1 4 3x1 4 2x1 4 1x1 4 Ti K Fe-Ti oxide x1 4 7x1 4 6x1 4 5x1 4 4x1 4 3x1 4 2x1 4 1x1 4 Fe-Ti-V-Cr oxide Cr V Mn Ti Fe Fe Channel Channel Ni K FeK Fe-Ni

9 Flux Flux Flux Flux Flux Track 41 slice XRS maps and spectra Ni K similar) 8 m 1 mm 8 m 8.x1 4 6.x1 4 Fe hotspot Fe hotspot 4.x x1 4 V in chromite FeCr2O4. is an extraterrestrial signature e.g. Alwmark & Schmitz Fe-Ti oxide 27 7x1 4 6x1 4 5x1 4 4x1 4 3x1 4 2x1 4 1x Ti K x1 4 7x1 4 6x1 4 5x1 4 4x1 4 3x1 4 2x1 4 1x1 4 Cr V Mn Ti Fe Fe red Cr Ka green Zn Ka blue Fe-Ti-V-Cr oxide Channel Channel Ni K FeK Fe-Ni

10 Normalised Absorbance Normalised Absorbance Track 41 slice Fe-XANES Pre edge feature 7111 ev shows presence of Fe Fe hotspot Iron Hotspot olivine Fe hotspot hematite..12 Hematite pyrrhotite.9 hematite Energy (ev) Energy (ev)

11 Normalised Absorbance FIT Track 41 slice Fe-XANES Best fit magnetite 38%, hematite 62% Fe Hotspot Magnetite Goethite Hematite Fit: Fe [(1-a)magnetite +a.hematite] a Hematite Energy (ev) Magnetite

12 Track 41 Fe-XANES FeNi has an absorbance feature at 716 ev Characteristic of metal (Pingitore et al. 22) Absorbance features A, ev and dashed line show presence of Fe 3+ FeNi has been partially oxidised CrVTiFe oxide Energy (ev)

13 Track XRS a 5 m Red ( ) 4 m pixels Green (Ni K ) Blue (Ca K ) c Fe-Ni grains mid track Fe hotspots concentrated towards terminal end Terminal Grain Fe-S

14 FIT Normalised Absorbance Track 134 mid track Fe oxide Fe Hotspot mid track Hematite Goethite Magnetite Energy (ev) Best fit to standards: 95% magnetite, 5% hematite Hematite a Magnetite

15 Normalised Absorbance Track 134 Terminal Grain Fe XANES Close fit to pyrrhotite standard over XANES, near edge region Terminal grain Pyrrhotite standard.2..5 mean difference fit, sd Energy (ev)

16 Conclusions XANES, TEM shows that Fe-bearing oxides are common in Comet Wild2 samples (e.g. in each of tracks 41, 121, 134) and have a variety of origins FeNi metal partially oxidised (Fe3+) during capture e.g. track 41 slice (near entrance) shown by Fe-XANES near edge structure Hematite-magnetite grains vary in proportion between the 2 minerals 5-68% Wild2 has an intermixed variety of oxidation states e.g. chromite, magnetite and FeNi metal, pyrrhotite (FeS) co-exist in same samples reminiscent of chondrites (Bridges et al. 29, MAPS) Next stage compare directly to chondrite groups