scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Stardust Interstellar Preliminary Examination XI: Identification and elemental analysis of impact craters on Al foils from the Stardust Interstellar Dust Collector

01 Sep 2014-Meteoritics & Planetary Science (John Wiley & Sons, Ltd)-Vol. 49, Iss: 9, pp 1698-1719
TL;DR: The Stardust Interstellar Preliminary Examination team analyzed thirteen Al foils from the NASA Stardust interstellar collector tray in order to locate candidate interstellar dust (ISD) grain impacts.
Abstract: The Stardust Interstellar Preliminary Examination team analyzed thirteen Al foils from the NASA Stardust interstellar collector tray in order to locate candidate interstellar dust (ISD) grain impacts. Scanning electron microscope (SEM) images reveal that the foils possess abundant impact crater and crater-like features. Elemental analyses of the crater features, with Auger electron spectroscopy, SEM-based energy dispersive X-ray (EDX) spectroscopy, and scanning transmission electron microscope-based EDX spectroscopy, demonstrate that the majority are either the result of impacting debris fragments from the spacecraft solar panels, or intrinsic defects in the foil. The elemental analyses also reveal that four craters contain residues of a definite extraterrestrial origin, either as interplanetary dust particles or ISD particles. These four craters are designated level 2 interstellar candidates, based on the crater shapes indicative of hypervelocity impacts and the residue compositions inconsistent with spacecraft debris.

Content maybe subject to copyright    Report

Citations
More filters
Journal ArticleDOI
15 Aug 2014-Science
TL;DR: The Stardust Interstellar Dust Collector captured seven particles and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream and more than 50 spacecraft debris particles were also identified as discussed by the authors.
Abstract: Seven particles captured by the Stardust Interstellar Dust Collector and returned to Earth for laboratory analysis have features consistent with an origin in the contemporary interstellar dust stream. More than 50 spacecraft debris particles were also identified. The interstellar dust candidates are readily distinguished from debris impacts on the basis of elemental composition and/or impact trajectory. The seven candidate interstellar particles are diverse in elemental composition, crystal structure, and size. The presence of crystalline grains and multiple iron-bearing phases, including sulfide, in some particles indicates that individual interstellar particles diverge from any one representative model of interstellar dust inferred from astronomical observations and theory.

176 citations

Journal ArticleDOI
15 Apr 2016-Science
TL;DR: The results show that, remarkably, these grains lack carbon-bearing compounds and have been homogenized in the interstellar medium into silicates with iron inclusions, which suggest the presence of magnesium-rich grains of silicate and oxide composition, partly with Iron inclusions.
Abstract: Interstellar dust (ISD) is the condensed phase of the interstellar medium. In situ data from the Cosmic Dust Analyzer on board the Cassini spacecraft reveal that the Saturnian system is passed by ISD grains from our immediate interstellar neighborhood, the local interstellar cloud. We determine the mass distribution of 36 interstellar grains, their elemental composition, and a lower limit for the ISD flux at Saturn. Mass spectra and grain dynamics suggest the presence of magnesium-rich grains of silicate and oxide composition, partly with iron inclusions. Major rock-forming elements (magnesium, silicon, iron, and calcium) are present in cosmic abundances, with only small grain-to-grain variations, but sulfur and carbon are depleted. The ISD grains in the solar neighborhood appear to be homogenized, likely by repeated processing in the interstellar medium.

102 citations

Journal Article
TL;DR: In this paper, the authors quantified the contribution of different microbial groups to absorption, backscattering, and marine reflectance during an El Nino-Southern Oscillation cold phase in the equatorial Pacific during the Etude du Broutage en Zone Equatoriale cruise on board the R/V L'Atalante.
Abstract: [1] Contributions of different microbial groups to absorption, backscattering, and marine reflectance (a(λ), b b (λ) and R(λ), respectively) were quantified during an El Nino-Southern Oscillation cold phase in the equatorial Pacific during the Etude du Broutage en Zone Equatoriale cruise on board the R/V L'Atalante. In situ data were collected at every degree of latitude from 8°S to 8°N, 180° (26 October to 13 November 1996), and satellite reflectances were available from POLDER-ADEOS for the 1-10 November 1996 decade. Bulk absorption and backscattering coefficients were estimated at 440 nm for the major microbial groups enumerated in the upper surface layer (heterotrophic bacteria, Prochlorococcus, Synechococcus, and <20-μm eukaryotic algae). Total absorption and backscattering coefficients were retrieved from space by a new inverse method. The observed ecosystem was typical of a well-developed equatorial upwelling, with maximal values of 0.4 mg m -3 for Tchl a, 0.026 m -1 for a p (440), 0.023 m -1 for a phy (440), and a low in situ a det (<14% of a p ). Prochlorococcus and nanoeukaryotic algae (3.4-μm mean diameter) were the dominant absorbers (97%), contributing about equally to a phy . The retrieved total absorption coefficient, a sat (440), from POLDER (maximum of 0.03 m -1 ) was higher than ap(440), as it included absorption by CDOM (estimated to be 15% of ap(440) + a w (440), where a w = absorption by pure water). Heterotrophic bacteria were the dominant contributors (73%) to total simulated microbial backscattering, b bmic (maximum = 3.7 × 10 -4 m -1 ), but b bmic was negligible compared to the inverted total backscattering by particles, b bp (2.7 x 10 -3 m -1 ), indicating that unidentified small nonliving particles contributed most to the satellite signal.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the trajectories of ISD in the solar system and the distribution of the impact speeds, directions, and flux of the ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission were predicted.
Abstract: On the basis of an interstellar dust model compatible with Ulysses and Galileo observations, we calculate and predict the trajectories of interstellar dust (ISD) in the solar system and the distribution of the impact speeds, directions, and flux of ISD particles on the Stardust Interstellar Dust Collector during the two collection periods of the mission. We find that the expected impact velocities are generally low (less than 10 km per second) for particles with the ratio of the solar radiation pressure force to the solar gravitational force beta greater than 1, and that some of the particles will impact on the cometary side of the collector. If we assume astronomical silicates for particle material and a density of 2 grams per cubic centimeter, and use the Ulysses measurements and the ISD trajectory simulations, we conclude that the total number of (detectable) captured ISD particles may be on the order of 50. In companion papers in this volume, we report the discovery of three interstellar dust candidates in the Stardust aerogel tiles. The impact directions and speeds of these candidates are consistent with those calculated from our ISD propagation model, within the uncertainties of the model and of the observations.

31 citations


Additional excerpts

  • ...A preliminary examination of the aerogel tiles on the interstellar side of the collector led to an identification of three candidate interstellar dust (ISD) particles (Westphal et al. 2014), and the examination of the aluminum foils resulted in four possible ISD impact craters (Stroud et al. 2014)....

    [...]

Journal ArticleDOI
TL;DR: In this paper, the authors report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector.
Abstract: We report the quantitative characterization by synchrotron soft X-ray spectroscopy of 31 potential impact features in the aerogel capture medium of the Stardust Interstellar Dust Collector. Samples were analyzed in aerogel by acquiring high spatial resolution maps and high energy-resolution spectra of major rock-forming elements Mg, Al, Si, Fe, and others. We developed diagnostic screening tests to reject spacecraft secondary ejecta and terrestrial contaminants from further consideration as interstellar dust candidates. The results support an extraterrestrial origin for three interstellar candidates: I1043,1,30 (Orion) is a 3 pg particle with Mg-spinel, forsterite, and an iron-bearing phase. I1047,1,34 (Hylabrook) is a 4 pg particle comprising an olivine core surrounded by low-density, amorphous Mg-silicate and amorphous Fe, Cr, and Mn phases. I1003,1,40 (Sorok) has the track morphology of a high-speed impact, but contains no detectable residue that is convincingly distinguishable from the background aerogel. Twenty-two samples with an anthropogenic origin were rejected, including four secondary ejecta from impacts on the Stardust spacecraft aft solar panels, nine ejecta from secondary impacts on the Stardust Sample Return Capsule, and nine contaminants lacking evidence of an impact. Other samples in the collection included I1029,1,6, which contained surviving solar system impactor material. Four samples remained ambiguous: I1006,2,18, I1044,2,32, and I1092,2,38 were too dense for analysis, and we did not detect an intact projectile in I1044,3,33. We detected no radiation effects from the synchrotron soft X-ray analyses; however, we recorded the effects of synchrotron hard X-ray radiation on I1043,1,30 and I1047,1,34.

19 citations


Additional excerpts

  • ...…2014); Sterken et al. (2014) predicted dust flux and trajectories based on Stardust flight information and dust propagation models; finally, a parallel ISPE effort to search and analyze impact craters in the Al foils, which separated aerogel tiles in the SIDC, is described by Stroud et al. (2014)....

    [...]

  • ...(Note that, in contrast, electron microscopy was a key ISPE technique for analysis of impact features in Al foils; Stroud et al. 2014.)...

    [...]

References
More filters
Journal ArticleDOI
TL;DR: The calculation of limits for small numbers of astronomical counts is based on standard equations derived from Poisson and binomial statistics; although the equations are straightforward, their direct use is cumbersome and involves both table-interpolations and several mathematical operations as discussed by the authors.
Abstract: The calculation of limits for small numbers of astronomical counts is based on standard equations derived from Poisson and binomial statistics; although the equations are straightforward, their direct use is cumbersome and involves both table-interpolations and several mathematical operations Convenient tables and approximate formulae are here presented for confidence limits which are based on such Poisson and binomial statistics The limits in the tables are given for all confidence levels commonly used in astrophysics

2,415 citations


"Stardust Interstellar Preliminary E..." refers background or methods in this paper

  • ...…(Table 1) on the two foils with candidate IS craters (1061N,1: 0.26– 11 cm 2; 1044N,1: 2.6–12 cm 2) is in statistical agreement with the average secondary crater density of 1.6–4.4 cm 2 within 1r uncertainty (Gehrels 1986), taking into account the random fluctuations in the sparse statistics....

    [...]

  • ...4 cm 2 within 1r uncertainty (Gehrels 1986), taking into account the random fluctuations in the sparse statistics....

    [...]

  • ...The 1r confidence range of secondary crater areal density is calculated as the 1r confidence interval (Gehrels 1986) of the number of secondary...

    [...]

Journal ArticleDOI
15 Dec 2006-Science
TL;DR: The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study, and preliminary examination shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin.
Abstract: The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

886 citations


Additional excerpts

  • ...Whereas the successful capture of Wild 2 grains was readily apparent from the first direct visual observations of the cometary collector tray (Brownlee et al. 2006), achieving a reasonable level of confidence that detectable interstellar grains were captured in the ISD collector tray has required a…...

    [...]

Journal ArticleDOI
15 Dec 2006-Science
TL;DR: Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials.
Abstract: Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single 17 O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is 16 O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

370 citations

Journal ArticleDOI
TL;DR: In this article, a review of the measurement processes and the interpretations needed to obtain actual isotope and element abundances from measurements is presented, with emphasis placed on descriptions of the measurements.
Abstract: Measurements of the present-day abundances of elements and isotopes, combined with model calculations, allow us to trace the history of nucleosynthesis in the universe. Throughout this review, emphasis will be placed on descriptions of the measurement processes and the interpretations needed to obtain actual isotope and element abundances from measurements. Comparisons of the abundances of isotopomers of a given element are less affected by systematic effects than are comparisons of the abundances of different elements. Thus ratios of isotopomers should be given a greater weight when data and models are compared. As is generally accepted, the universe began with an explosive event, the Big Bang. The nucleosynthesis associated with this event produced `primordial' abundances of the `light elements', deuterium, , , and . Subsequent stellar processing of the light elements has altered the relative abundances, and also produced heavier elements such as carbon, nitrogen and oxygen. Stellar nucleosynthesis products from solar and larger mass stars are expelled into the interstellar medium (ISM). The goal of studies of the abundances of the light elements is to estimate the primordial abundances, that is, the abundances produced in the Big Bang. It is believed that D is always net destroyed in stars; and may be net produced, is certainly net produced. In the Solar System itself, results are obtained from in situ measurements with space probes to Jupiter, measurements of solar wind constituents, the analysis of the content of meteorites, and spectral line measurements of the solar photosphere. For sources outside the Solar System, these data are based on spectral line measurements of gas-phase species. The ratio of gas-phase abundances of elements, such as carbon to lithium may be affected by differing amounts of condensation onto dust grains; however such a process will not affect the ratio of isotopes such as . The most reliable measurements of D to H ratios are based on spectroscopic measurements of Lyman series ultraviolet absorption lines from foreground interstellar gas. Measurements of clouds in our galaxy have been obtained with satellites such as the International Ultraviolet Observatory, Copernicus, and the Hubble Space Telescope. The most interesting new development is the measurement of distant clouds with large redshifted velocities. Such data can be taken with Earth-bound optical telescopes. In the near future the Far Ultra Violet Explorer will refine and extend measurements of D/H ratios in relatively nearby regions. Abundances of in the ISM have been measured using the hyperfine transition of , in galactic H II regions which are ionized by high-mass stars. is the most abundant of the light elements. The primordial abundance must be very accurately determined if one wishes to use this quantity to estimate the baryon density in the early universe. Recently /H ratios have been measured in a number of metal-poor compact blue galaxies. These sources seem to have had little stellar evolution, so the ratio should be close to the primordial value. Estimates of the primordial abundance of are made for a population of old stars found far from the plane of our galaxy. A refinement of Li abundance estimates requires a more detailed understanding of the Li destruction processes in stars.

323 citations

Journal ArticleDOI
15 Dec 2006-Science
TL;DR: Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth.
Abstract: Particles emanating from comet 81P/Wild 2 collided with the Stardust spacecraft at 6.1 kilometers per second, producing hypervelocity impact features on the collector surfaces that were returned to Earth. The morphologies of these surprisingly diverse features were created by particles varying from dense mineral grains to loosely bound, polymineralic aggregates ranging from tens of nanometers to hundreds of micrometers in size. The cumulative size distribution of Wild 2 dust is shallower than that of comet Halley, yet steeper than that of comet Grigg-Skjellerup.

308 citations

Related Papers (5)