Brit Hvide

Bio: Brit Hvide is an academic researcher from Field Museum of Natural History. The author has contributed to research in topics: Cosmic dust & Interstellar medium. The author has an hindex of 11, co-authored 12 publications receiving 222 citations.

Final reports of the Stardust Interstellar Preliminary Examination

Abstract: With the discovery of bona fide extraterrestrial materials in the Stardust Interstellar Dust Collector, NASA now has a fundamentally new returned sample collection, after the Apollo, Antarctic meteorite, Cosmic Dust, Genesis, Stardust Cometary, Hayabusa, and Exposed Space Hardware samples. Here, and in companion papers in this volume, we present the results from the Preliminary Examination of this collection, the Stardust Interstellar Preliminary Examination (ISPE). We found extraterrestrial materials in two tracks in aerogel whose trajectories and morphology are consistent with an origin in the interstellar dust stream, and in residues in four impacts in the aluminum foil collectors. While the preponderance of evidence, described in detail in companion papers in this volume, points toward an interstellar origin for some of these particles, alternative origins have not yet been eliminated, and definitive tests through isotopic analyses were not allowed under the terms of the ISPE. In this summary, we answer the central questions of the ISPE: How many tracks in the collector are consistent in their morphology and trajectory with interstellar particles? How many of these potential tracks are consistent with real interstellar particles, based on chemical analysis? Conversely, what fraction of candidates are consistent with either a secondary or interplanetary origin? What is the mass distribution of these particles, and what is their state? Are they particulate or diffuse? Is there any crystalline material? How many detectable impact craters (> 100 nm) are there in the foils, and what is their size distribution? How many of these craters have analyzable residue that is consistent with extraterrestrial material? And finally, can craters from secondaries be recognized through crater morphology (e.g., ellipticity)?

Stardust Interstellar Preliminary Examination X: Impact speeds and directions of interstellar grains on the Stardust dust collector

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.

Stardust Interstellar Preliminary Examination I: Identification of tracks in aerogel

Abstract: –Here, we report the identification of 69 tracks in approximately 250 cm 2 of aerogelcollectors of the Stardust Interstellar Dust Collector. We identified these tracks throughStardust@home, a distributed internet-based virtual microscope and search engine, in which> 30,000 amateur scientists collectively performed >9 9 10 7 searches on approximately 10 6 fields of view. Using calibration images, we measured individual detection efficiency, andfound that the individual detection efficiency for tracks > 2.5 lm in diameter was >0.6, andwas >0.75 for tracks >3 lm in diameter. Because most fields of view were searched >30times, these results could be combined to yield a theoretical detection efficiency near unity.The initial expectation was that interstellar dust would be captured at very high speed. Theactual tracks discovered in the Stardust collector, however, were due to low-speed impacts,and were morphologically strongly distinct from the calibration images. As a result, thedetection efficiency of these tracks was lower than detection efficiency of calibrationspresented in training, testing, and ongoing calibration. Nevertheless, as calibration imagesbased on low-speed impacts were added later in the project, detection efficiencies for low-speed tracks rose dramatically. We conclude that a massively distributed, calibrated search,with amateur collaborators, is an effective approach to the challenging problem ofidentification of tracks of hypervelocity projectiles captured in aerogel.1510 A. J. Westphal et al.

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

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.

Stardust Interstellar Preliminary Examination IV: Scanning transmission X-ray microscopy analyses of impact features in 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.

Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft

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.

The Stardust Mission: Analyzing Samples from the Edge of the Solar System

Abstract: Comet samples returned to Earth by the NASA Stardust mission have provided a surprising glimpse into the nature of early Solar System materials and an epiphany on the origin of the initial rocky materials that once filled the cold regions of the solar nebula. The findings show that the cold regions of the early Solar System were not isolated and were not a refuge where interstellar materials could commonly survive. Wild 2, the sampled comet, appears to be a typical active Jupiter family comet, and yet most of its sampled micron and larger grains are familiar high-temperature meteoritic materials, such as chondrule fragments, that were transported to cold nebular regions. The rocky components in primitive asteroids and comets may differ because asteroid formation was dominated by local materials, whereas comets formed from mixed materials, many of which were transported from very distant locations.

Flux and composition of interstellar dust at Saturn from Cassini's Cosmic Dust Analyzer.

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.

X-ray computed tomography of planetary materials: A primer and review of recent studies

Abstract: X-ray computed tomography (XCT) is a powerful 3D imaging technique that has been used to investigate meteorites, mission-returned samples, and other planetary materials of all scales from dust particles to large rocks. With this technique, a 3D volume representing the X-ray attenuation (which is sensitive to composition and density) of the materials within an object is produced, allowing various components and textures to be observed and quantified. As with any analytical technique, a thorough understanding of the underlying physical principles, system components, and data acquisition parameters provides a strong foundation for the optimal acquisition and interpretation of the data. Here we present a technical overview of the physics of XCT, describe the major components of a typical laboratory-based XCT instrument, and provide a guide for how to optimize data collection for planetary materials using such systems. We also discuss data processing, visualization and analysis, including a discussion of common data artifacts and how to minimize them. We review a variety of recent studies in which XCT has been used to study extraterrestrial materials and/or to address fundamental problems in planetary science. We conclude with a short discussion of anticipated future directions of XCT technology and application.

2016 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry and its applications

Abstract: This review describes advances in the XRF group of techniques published approximately between April 2015 and March 2016. Fundamental contributions in the instrumentation sections include the development of synchrotron radiation sources, semiconductor design technology and evaluating the quality of in situ hand-held XRF results. A bench top TXRF spectrometer for the measurement of the elements from carbon to uranium is described that offers achievable detection limits that range from ng g−1 to μg g−1. The applications sections aim to give a representative overview of the range of applications that use XRF techniques with an emphasis on papers that describe technical or application innovation. Sample size investigated ranged from the planet Mercury down to nano-gram quantities of cement secreted by settlement stage barnacle larvae. The archaeological and cultural heritage section this year includes an authentic report on the use of cannabis as a filler in ancient lime plaster and heartening news that the construction of an underground parking garage in the centre of Zurich (Switzerland) unearthed the remains of seven Neolithic settlements from the 4th and 3rd millennium BC. The X-ray excitation of iron present in ancient iron-gall inks was presented as a step toward the non-invasive reading of fragile and/or unopenable documents. Feedback from readers of this review is most welcome and the review coordinator may be contacted using the email address provided.