Author
Ariel Leonard
Other affiliations: University of Washington
Bio: Ariel Leonard is an academic researcher from Washington University in St. Louis. The author has contributed to research in topics: Cosmic dust & Interstellar medium. The author has an hindex of 12, co-authored 17 publications receiving 403 citations. Previous affiliations of Ariel Leonard include University of Washington.
Papers
More filters
University of California, Berkeley1, United States Naval Research Laboratory2, Lawrence Berkeley National Laboratory3, Goethe University Frankfurt4, State University of New York at Plattsburgh5, Jacobs Engineering Group6, Heidelberg University7, Carnegie Institution for Science8, Field Museum of Natural History9, University of Leicester10, University of Washington11, University of Kent12, Ghent University13, University of New Mexico14, European Synchrotron Radiation Facility15, University of Chicago16, Washington University in St. Louis17, Max Planck Society18, International Space Science Institute19, Natural History Museum20, Argonne National Laboratory21, École normale supérieure de Lyon22, university of lille23, Ames Research Center24, University of Stuttgart25, Jet Propulsion Laboratory26
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
Space Sciences Laboratory1, Lawrence Berkeley National Laboratory2, Goethe University Frankfurt3, State University of New York at Plattsburgh4, Heidelberg University5, University of Stuttgart6, Braunschweig University of Technology7, Empik8, United States Naval Research Laboratory9, Field Museum of Natural History10, University of Leicester11, University of Washington12, University of Kent13, European Synchrotron Radiation Facility14, George Washington University15, University of Chicago16, Washington University in St. Louis17, Max Planck Society18, Natural History Museum19, Argonne National Laboratory20, École normale supérieure de Lyon21, university of lille22, Carnegie Institution for Science23, Ames Research Center24, Ghent University25, Jet Propulsion Laboratory26, Osaka University27
TL;DR: The results from the preliminary examination of this collection, the Stardust Interstellar Preliminary Examination (ISPE), were presented in this article, where extraterrestrial materials were found 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.
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)?
35 citations
University of Stuttgart1, Braunschweig University of Technology2, University of California, Berkeley3, European Space Agency4, Max Planck Society5, Heidelberg University6, Field Museum of Natural History7, United States Naval Research Laboratory8, Lawrence Berkeley National Laboratory9, Goethe University Frankfurt10, University of Leicester11, University of Washington12, University of Kent13, European Synchrotron Radiation Facility14, University of New Mexico15, University of Chicago16, Washington University in St. Louis17, State University of New York at Plattsburgh18, Natural History Museum19, Argonne National Laboratory20, École Normale Supérieure21, Carnegie Institution for Science22, Ames Research Center23, Ghent University24, Jet Propulsion Laboratory25
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
Space Sciences Laboratory1, Durham University2, Field Museum of Natural History3, United States Naval Research Laboratory4, Lawrence Berkeley National Laboratory5, Goethe University Frankfurt6, University of Leicester7, University of Washington8, University of Kent9, European Synchrotron Radiation Facility10, George Washington University11, University of Chicago12, Washington University in St. Louis13, State University of New York at Plattsburgh14, Max Planck Society15, Heidelberg University16, Natural History Museum17, Argonne National Laboratory18, École normale supérieure de Lyon19, university of lille20, Carnegie Institution for Science21, Ames Research Center22, Ghent University23, University of Stuttgart24, Jet Propulsion Laboratory25, Osaka University26
TL;DR: In this paper, Westphal et al. reported the identification of 69 tracks in approximately 250 cm 2 of aerogelcollectors of the Stardust Interstellar Dust Collector using a distributed internet-based virtual microscope and search engine.
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.
23 citations
United States Naval Research Laboratory1, Field Museum of Natural History2, Space Sciences Laboratory3, Lawrence Berkeley National Laboratory4, Goethe University Frankfurt5, University of Leicester6, University of Washington7, University of Kent8, European Synchrotron Radiation Facility9, George Washington University10, University of Chicago11, Washington University in St. Louis12, State University of New York at Plattsburgh13, Max Planck Society14, Heidelberg University15, Natural History Museum16, Sandia National Laboratories17, Argonne National Laboratory18, École normale supérieure de Lyon19, Carnegie Institution for Science20, University of Hawaii at Manoa21, Ames Research Center22, Ghent University23, Braunschweig University of Technology24, University of Stuttgart25, Jet Propulsion Laboratory26, Osaka University27
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.
22 citations
Cited by
More filters
TL;DR: In this article, the authors consider the extensive experimental and computer simulation studies that have been performed over the past several decades on what the nature of the primary damage is, and provide alternatives to the current international standard for quantifying this energetic particle damage, the Norgett-Robinson-Torrens displacements per atom (NRT-dpa) model for metals.
334 citations
TL;DR: The THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids) model as discussed by the authors is based upon a core model that was developed to explain the dust extinction and emission in the diffuse interstellar medium.
Abstract: Here we introduce the interstellar dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids), which takes a global view of dust and its evolution in response to the local conditions in interstellar media. This approach is built upon a core model that was developed to explain the dust extinction and emission in the diffuse interstellar medium. The model was then further developed to self-consistently include the effects of dust evolution in the transition to denser regions. The THEMIS approach is under continuous development and currently we are extending the framework to explore the implications of dust evolution in HII regions and the photon-dominated regions associated with star formation. We provide links to the THEMIS, DustEM and DustPedia websites where more information about the model, its input data and applications can be found.
204 citations
TL;DR: The THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids) model as discussed by the authors is based on a core model that was developed to explain the dust extinction and emission in the diffuse interstellar medium.
Abstract: Here we introduce the interstellar dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids), which takes a global view of dust and its evolution in response to the local conditions in interstellar media. This approach is built upon a core model that was developed to explain the dust extinction and emission in the diffuse interstellar medium. The model was then further developed to self-consistently include the effects of dust evolution in the transition to denser regions. The THEMIS approach is under continuous development and we are currently extending the framework to explore the implications of dust evolution in HII regions and the photon-dominated regions associated with star formation. We provide links to the THEMIS, DustEM and DustPedia websites where more information about the model, its input data and applications can be found.
199 citations
University of California, Berkeley1, United States Naval Research Laboratory2, Lawrence Berkeley National Laboratory3, Goethe University Frankfurt4, State University of New York at Plattsburgh5, Jacobs Engineering Group6, Heidelberg University7, Carnegie Institution for Science8, Field Museum of Natural History9, University of Leicester10, University of Washington11, University of Kent12, Ghent University13, University of New Mexico14, European Synchrotron Radiation Facility15, University of Chicago16, Washington University in St. Louis17, Max Planck Society18, International Space Science Institute19, Natural History Museum20, Argonne National Laboratory21, École normale supérieure de Lyon22, university of lille23, Ames Research Center24, University of Stuttgart25, Jet Propulsion Laboratory26
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
TL;DR: In this article, the authors show that the cold regions of the early Solar System were not isolated and were not a refuge where interstellar materials could commonly survive, and that 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.
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.
148 citations