[Show abstract][Hide abstract] ABSTRACT: A 4 × 6 μm terminal particle from Stardust track 130, named Bidi, is composed of a refractory assemblage of Fo97 olivine, Al- and Ti-bearing clinopyroxene and anorthite feldspar (An97). Mineralogically, Bidi resembles a number of components found in primitive chondritic meteorites including Al-rich chondrules, plagioclase-bearing type I ferromagnesian chondrules and amoeboid olivine aggregates (AOAs). Measured widths of augite/pigeonite lamellae in the clinopyroxene indicate fast cooling rates suggesting that Bidi is more likely to be a chondrule fragment than an AOA. Bulk element concentrations, including an Al2O3 content of 10.2 wt%, further suggests that Bidi is more akin to Al-rich rather than ferromagnesian chondrules. This is supported by high anorthite content of the plagioclase feldspar, overall bulk composition and petrogenetic analysis using a cosmochemical Al2O3–Ca2SiO4–Mg2SiO4 phase diagram. Measured minor element abundances of individual minerals in Bidi generally support an Al-rich chondrule origin but are not definitive between any of the object types. Oxygen isotope ratios obtained from olivine (+minor high-Ca pyroxene)fall between the TF and CCAM lines and overlap similar minerals from chondrules in primitive chondrites but are generally distinct from pristine AOA minerals. Oxygen isotope ratios are similar to some minerals from both Al-rich and type I ferromagnesian chondrules in unequilibrated carbonaceous, enstatite and ordinary chondrites. Although no single piece of evidence uniquely identifies Bidi as a particular object type, the preponderance of data, including mineral assemblage, bulk composition, mineral chemistry, inferred cooling rates and oxygen isotope ratios, suggest that Bidi is more closely matched to Al-rich chondrules than AOAs or plagioclase-bearing type I ferromagnesian chondrules and likely originated in a chondrule-forming region in the inner solar system.
Full-text · Article · Nov 2014 · Geochimica et Cosmochimica Acta
[Show abstract][Hide abstract] ABSTRACT: We analyzed carbonaceous materials in the two main morphological types of Stardust tracks (A, and B). We analyzed 71 particles (∼1–10 μm in size) distributed along these tracks with transmission electron microscopy (TEM) and found carbon associated with 16 of them. The carbonaceous materials occur in five distinct morphologies: graphitic, smooth, dirty, spongy and globular, covering most of the range of morphologies observed in primitive meteorites and interplanetary dust particles. We measured N and C isotopic compositions on 5 of these particles and found that all but one have terrestrial isotopic compositions. The anomalous particle had a moderate 15N enrichment (δ15N = 150 ± 36‰, 2σ) and both globular and spongy morphologies. The carbonaceous materials are not preferentially associated with particles of a particular size but are randomly distributed in all three tracks.
No preview · Article · Sep 2013 · Geochimica et Cosmochimica Acta
[Show abstract][Hide abstract] ABSTRACT: A new CAI from comet Wild 2 is the third CAI discovered in a Stardust
track and is mineralogically and texturally similar to fine-grained
anorthite-spinel inclusions from reduced CV chondrites which were likely
precursors to type C CAIs.
[Show abstract][Hide abstract] ABSTRACT: We analyzed 2 ultra-carbonaceous interplanetary dust particles and 2 cometary
Wild 2 particles with infrared spectroscopy. We characterized the carrier of
the 3.4 micron band in these samples and compared its profile and the CH2/CH3
ratios to the 3.4 micron band in the diffuse interstellar medium (DISM), in the
insoluble organic matter (IOM) from 3 primitive meteorites, in asteroid 24
Themis and in the coma of comet 103P/Hartley 2. We found that the 3.4 micron
band in both Wild 2 and IDPs is similar, but different from all the other
astrophysical environments that we compared to. The 3.4 micron band in IDPs and
Wild 2 particles is dominated by CH2 groups, the peaks are narrower and
stronger than in the meteorites, asteroid Themis, and the DISM. Also, the
presence of the carbonyl group C=O at 1700 cm-1 (5.8 micron) in most of the
spectra of our samples, indicates that these aliphatic chains have O bonded to
them, which is quite different from astronomical spectra of the DISM. Based on
all these observations we conclude that the origin of the carrier of the 3.4
micron band in IDPs and Wild 2 samples is not interstellar, instead, we suggest
that the origin lies in the outermost parts of the solar nebula.
Full-text · Article · Jan 2013 · The Astrophysical Journal
[Show abstract][Hide abstract] ABSTRACT: Highlights
► We analyzed oxygen isotope ratios of nine crystalline silicates from comet Wild 2. ► Oxygen isotope ratios are highly variable: 16O-rich to 16O-poor. ► 16O-rich Mn-rich forsterites may be condensates from an 16O-rich solar nebula gas. ► Δ17O-Mg# trend of 16O-poor silicates resembles that of CR chondrite chondrules. ► Many of Wild 2 silicates may have been transported from the outer asteroid belt.
No preview · Article · Dec 2012 · Earth and Planetary Science Letters
[Show abstract][Hide abstract] ABSTRACT: Transmission electron microscopy examination of 87 large fragments from
16 carrot-shaped and bulbous Stardust (SD) tracks was performed to study
the range and diversity of materials present in comet Wild 2. Olivines
and low-Ca pyroxenes represent the largest proportions of fragments
observed; however, a wide range of minerals and rocks were found
including probable ferromagnesian, Al-rich and Si-rich chondrule
fragments, a refractory inclusion, possible matrix mineral/lithic
clasts, and probable condensate minerals. These materials, combined with
fine-grained components in the tracks, are analogous to components in
unequilibrated chondrite meteorites and cluster interplanetary dust
particles (IDPs). Two unusual lithologies in the bulbous tracks are only
observed in chondritic porous IDPs and may have direct links to IDPs.
The absence of phyllosilicates indicates that comet Wild 2 may be a
"dry" comet that did not accrete or form significant amounts of hydrated
phases. Some large mineral fragments in the SD tracks are analogous to
large mineral IDPs. The large variations of the coarse-grained
components within and between all 16 tracks show that comet Wild 2 is
mineralogically diverse and unequilibrated on nearly all scales and must
have accreted materials from diverse source regions that were widely
dispersed throughout the solar nebula.
[Show abstract][Hide abstract] ABSTRACT: The solid 2-10 μm samples of comet Wild 2 provide a limited but
direct view of the solar nebula solids that accreted to form Jupiter
family comets. The samples collected by the Stardust mission are
dominated by high-temperature materials that are closely analogous to
meteoritic components. These materials include chondrule and CAI-like
fragments. Five presolar grains have been discovered, but it is clear
that isotopically anomalous presolar grains are only a minor fraction of
the comet. Although uncertain, the presolar grain content is perhaps
higher than found in chondrites and most interplanetary dust particles.
It appears that the majority of the analyzed Wild 2 solids were produced
in high-temperature "rock forming" environments, and they were then
transported past the orbit of Neptune, where they accreted along with
ice and organic components to form comet Wild 2. We hypothesize that
Wild 2 rocky components are a sample of a ubiquitously distributed flow
of nebular solids that was accreted by all bodies including planets and
meteorite parent bodies. A primary difference between asteroids and the
rocky content of comets is that comets are dominated by this widely
distributed component. Asteroids contain this component, but are
dominated by locally made materials that give chondrite groups their
distinctive properties. Because of the large radial mixing in this
scenario, it seems likely that most comets contain a similar mix of
rocky materials. If this hypothesis is correct, then properties such as
oxygen isotopes and minor element abundances in olivine, should have a
wider dispersion than in any chondrite group, and this may be a
characteristic property of primitive outer solar system bodies made from
widely transported components.
[Show abstract][Hide abstract] ABSTRACT: Eight ferromagnesian Wild 2 particles show diverse oxygen isotope ratios
and chemistry: ^1^6O-rich (Mn-rich forsterite) and ^1^6O-poor (FeO-rich
and -poor), similar to AOAs and chondrules in CR chondrites. This
suggests a genetic link to CR chondrites.
[Show abstract][Hide abstract] ABSTRACT: We compared the organic carbonaceous material in a stardust particle and
an IDP and found that texturally the material is identical but the IR
data in the IDP shows many more peaks and variability than the SD
[Show abstract][Hide abstract] ABSTRACT: TEM studies of large fragments from Stardust track 77 indicate that
Comet Wild 2 is mineralogically heterogeneous on the micrometer scale.
Isotopic measurements further suggest the fragments were derived from
diverse source regions in the nebula.
[Show abstract][Hide abstract] ABSTRACT: Abstract– Coordinated in situ transmission electron microscopy and isotopic measurements of carbonaceous phases in interplanetary dust particles were performed to determine their origins. Five different types of carbonaceous materials were identified based on their morphology and texture, observed by transmission electron microscopy: globular, vesicular, dirty, spongy, and smooth. Flash heating experiments were performed to explore whether some of these morphologies are the result of atmospheric entry processes. Each of these morphologies was found to have isotopically anomalous H and N. Rare C isotopic anomalies were also observed. The isotopic and morphological properties of several of these phases, particularly the organic globules, are remarkably similar to those observed in other extraterrestrial materials including carbonaceous chondrites, comet 81P/Wild 2 particles collected by the Stardust spacecraft, and Antarctic micrometeorites, indicating that they were widespread in the early solar system. The ubiquitous nature and the isotopic anomalies of the nanoglobules and some other morphologies strongly suggest that these are very primitive phases. Given that some of the isotopic anomalies (D and 15N excesses) are indicative of mass fractionation chemical reactions in a very cold environment, and some others (13C and 15N depletions) have other origins, these carbonaceous phases come from different reservoirs. Whatever their origins, these materials probably reflect the first stages of the evolution of solar system organic matter, having originated in the outermost regions of the protosolar disk and/or interstellar cold molecular clouds.
[Show abstract][Hide abstract] ABSTRACT: Abstract– We optically classified 5682 micrometeorites (MMs) from the 2000 South Pole collection into textural classes, imaged 2458 of these MMs with a scanning electron microscope, and made 200 elemental and eight isotopic measurements on those with unusual textures or relict phases. As textures provide information on both degree of heating and composition of MMs, we developed textural sequences that illustrate how fine-grained, coarse-grained, and single mineral MMs change with increased heating. We used this information to determine the percentage of matrix dominated to mineral dominated precursor materials (precursors) that produced the MMs. We find that at least 75% of the MMs in the collection derived from fine-grained precursors with compositions similar to CI and CM meteorites and consistent with dynamical models that indicate 85% of the mass influx of small particles to Earth comes from Jupiter family comets. A lower limit for ordinary chondrites is estimated at 2–8% based on MMs that contain Na-bearing plagioclase relicts. Less than 1% of the MMs have achondritic compositions, CAI components, or recognizable chondrules. Single mineral MMs often have magnetite zones around their peripheries. We measured their isotopic compositions to determine if the magnetite zones demarcate the volume affected by atmospheric exchange during entry heating. Because we see little gradient in isotopic composition in the olivines, we conclude that the magnetites are a visual marker that allows us to select and analyze areas not affected by atmospheric exchange. Similar magnetite zones are seen in some olivine and pyroxene relict grains contained within MMs.
[Show abstract][Hide abstract] ABSTRACT: Two Wild-2 particles and three anhydrous IDPs show oxygen isotope ratios similar to those of other Wild-2 particles, anhydrous IDPs, and carbonaceous chondrite chondrules, suggesting the presence of the common oxygen isotope reservoir.
[Show abstract][Hide abstract] ABSTRACT: The large solid particles in comet Wild 2 may represent a large particle
component that was distributed to all early bodies in the solar nebula.
This hypothesis is tested by comparing large solid particles from a
variety of cometary sources.
[Show abstract][Hide abstract] ABSTRACT: Large mineral and rock fragments studied in 16 SD tracks represent a wide range of materials that formed in the nebula including chondrules, RI's, mineral grains and unequilibrated minerals and rock assemblages that are analogous to cluster IDPs or chondrite matrix.