David Anderson

Bio: David Anderson is an academic researcher from Space Sciences Laboratory. The author has contributed to research in topics: Cosmic dust & Interstellar medium. The author has an hindex of 12, co-authored 12 publications receiving 240 citations. Previous affiliations of David Anderson include University of California, Berkeley.

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.

Cord blood high density lipoproteins: Leningrad and Cincinnati.

Abstract: Summary: Adult Russian males (ages 40-49) have recently been shown, in collaborative Lipid Research Clinic (LRC) studies, to have substantially higher (8-10 mg/dl) plasma high-density lipoprotein cholesterol (C-HDL) than adult American males. Since C-HDL has a powerful inverse correlation with the risk of developing coronary heart disease, elucidation of the etiology of cross-cultural differences in C-HDL may be important in developing approaches to prevent or ameliorate coronary heart disease. This LRC study, using identically standardized LRC laboratories, focused on cord blood C-HDL in 423 neonates of Leningrad (USSR) and 425 neonates of Cincinnati (USA) to determine whether, like Russian adults, Russian neonates had higher C-HDL levels. Mean C-HDL levels in male and female American neonates were slightly (1-2 mg/dl), but not significantly higher (P = 0.22, 0.22) than in male and female Russian neonates, respectively. In subsets of the neonate American (260 of 425) and Russian (174 of 423) groups, mean C-HDL levels were 3 mg/dl and 3 mg/dl higher, respectively, in male and female American neonates than in their Russian counterparts, and these small mean differences were statistically significant, P < 0.025. Thus, adult Russian-American differences in C-HDL were not echoed by comparisons of neonates, using identical laboratory methods for lipoprotein determination. The within-culture, cross-sex comparisons of cord blood lipids and lipoproteins, did, however, parallel findings in older children and young adults. Both female American and Russian neonates had higher C-HDL levels than did males (P = 0.001, 0.002). Within the limits of inheritance as expressed by cord blood lipoproteins, the dichotomy between Russian and American neonates and adults for C-HDL suggests that higher adult Russian C-HDL levels may possibly reflect an aggregate of variables grouped under the term "environmental effect." Speculation: Because population studies and studies of kindreds with familial hyper-α-lipoproteinemia reveal a strong inverse correlation of C-HDL with coronary heart disease, the elucidation of the etiology of cross-cultural and cross-racial differences in C-HDL might have considerable importance in identifying "protective" environmental differences relevant to development of coronary heart disease.

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.