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Title: Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust

Abstract

We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed ({approx}180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930144
Report Number(s):
BNL-80800-2008-JA
Journal ID: ISSN 0193-4511; SCEHDK; TRN: US200822%%1202
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Science; Journal Volume: 314; Journal Issue: 5806
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; COMETS; DUSTS; METEORITES; CHEMICAL COMPOSITION; national synchrotron light source

Citation Formats

Flynn,G., Bleuet, P., Borg, J., Bradley, J., Brenker, F., Brennan, S., Bridges, J., Brownlee, D., Bullock, E., and et al. Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust. United States: N. p., 2006. Web. doi:10.1126/science.1136141.
Flynn,G., Bleuet, P., Borg, J., Bradley, J., Brenker, F., Brennan, S., Bridges, J., Brownlee, D., Bullock, E., & et al. Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust. United States. doi:10.1126/science.1136141.
Flynn,G., Bleuet, P., Borg, J., Bradley, J., Brenker, F., Brennan, S., Bridges, J., Brownlee, D., Bullock, E., and et al. Sun . "Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust". United States. doi:10.1126/science.1136141.
@article{osti_930144,
title = {Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust},
author = {Flynn,G. and Bleuet, P. and Borg, J. and Bradley, J. and Brenker, F. and Brennan, S. and Bridges, J. and Brownlee, D. and Bullock, E. and et al.},
abstractNote = {We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed ({approx}180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.},
doi = {10.1126/science.1136141},
journal = {Science},
number = 5806,
volume = 314,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • No abstract prepared.
  • NASA's Stardust spacecraft collected dust from the coma of Comet 81P/Wild 2 by impact into aerogel capture cells or into Al-foils. The first direct, laboratory measurement of the physical, chemical, and mineralogical properties of cometary dust grains ranging from <10-15 to ?10-4 g were made on this dust. Deposition of material along the entry tracks in aerogel and the presence of compound craters in the Al-foils both indicate that many of the Wild 2 particles in the size range sampled by Stardust are weakly bound aggregates of a diverse range of minerals. Mineralogical characterization of fragments extracted from tracks indicatesmore » that most tracks were dominated by olivine, low-Ca pyroxene, or Fe-sulfides, although one track was dominated by refractory minerals similar to Ca-Al inclusions in primitive meteorites. Minor mineral phases, including Cu-Fe-sulfide, Fe-Zn-sulfide, carbonate and metal oxides, were found along some tracks. The high degree of variability of the element/Fe ratios for S, Ca, Ti, Cr, Mn, Ni, Cu, Zn, and Ga among the 23 tracks from aerogel capture cells analyzed during Stardust Preliminary Examination is consistent with the mineralogical variability. This indicates Wild 2 particles have widely varying compositions at the largest size analyzed (>10 ?m). Because Stardust collected particles from several jets, sampling material from different regions of the interior of Wild 2, these particles are expected to be representative of the non-volatile component of the comet over the size range sampled. Thus, the stream of particles associated with Comet Wild 2 contains individual grains of diverse elemental and mineralogical compositions, some rich in Fe and S, some in Mg, and others in Ca and Al. The mean refractory element abundance pattern in the Wild 2 particles that were examined is consistent with the CI meteorite pattern for Mg, Si, Cr, Fe, and Ni to 35%, and for Ca, Ti and Mn to 60%, but S/Si and Fe/Si both show a statistically significant depletion from the CI values and the moderately volatile elements Cu, Zn, Ga are enriched relative to CI. This elemental abundance pattern is similar to that in anhydrous, porous interplanetary dust particles (IDPs), suggesting that, if Wild 2 dust preserves the original composition of the Solar Nebula, the anhydrous, porous IDPs, not the CI meteorites, may best reflect the Solar Nebula abundances. This might be tested by elemental composition measurements on cometary meteors.« less
  • Infrared spectra of material captured from comet 81P/Wild 2 by the Stardust spacecraft reveal indigenous aliphatic hydrocarbons similar to those in interplanetary dust particles thought to be derived from comets, but with longer chain lengths than those observed in the diffuse interstellar medium. Similarly, the Stardust samples contain abundant amorphous silicates in addition to crystalline silicates such as olivine and pyroxene. The presence of crystalline silicates in Wild 2 is consistent with mixing of solar system and interstellar matter. No hydrous silicates or carbonate minerals were detected, which suggests a lack of aqueous processing of Wild 2 dust.
  • Among the samples returned from comet 81P/Wild 2 by the Stardust spacecraft is a suite of particles from one impact track (Track 25) that are Ca-, Al-rich and FeO-free. We studied three particles from this track that range in size from 5.3 x 3.2 {micro}m to 15 x 10 {micro}m. Scanning and transmission electron microscopy show that they consist of very fine-grained (from {approx}0.5 to {approx}2 {micro}m) Al-rich, Ti-bearing and Ti-free clinopyroxene, Mg-Al spinel, anorthite, perovskite, and osbornite (TiN). In addition to these phases, the terminal particle, named 'Inti', also contains melilite. All of these phases, with the exception ofmore » osbornite, are common in refractory inclusions and are predicted to condense at high temperature from a gas of solar composition. Osbornite, though very rare, has also been found in meteoritic refractory inclusions, and could have formed in a region of the nebula where carbon became enriched relative to oxygen compared to solar composition. Compositions of Ti-pyroxene in Inti are similar, but not identical, to those of fassaite from Allende inclusions. Electron energy loss spectroscopy shows that Ti-rich pyroxene in Inti has Ti{sup 3+}/Ti{sup 4+} within the range of typical meteoritic fassaite, consistent with formation under reducing conditions comparable to those of a system of solar composition. Inti is {sup 16}O-rich, with {delta}{sup 18}O {approx} {delta}{sup 17}O {approx} 40{per_thousand}, like unaltered phases in refractory inclusions and refractory IDPs. With grain sizes, mineralogy, mineral chemistry, and an oxygen isotopic composition like those of refractory inclusions, we conclude that Inti is a refractory inclusion that formed in the inner solar nebula. Identification of a particle that formed in the inner Solar System among the comet samples demonstrates that there was transport of materials from the inner to the outer nebula, probably either in a bipolar outflow or by turbulence.« less