Showing papers by "Eberhard Grün published in 2014"

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.

Micrometeoroid impact charge yield for common spacecraft materials

Abstract: The impact ionization charge yield is experimentally measured from four common materials used in space and specifically on the two STEREO spacecraft (germanium-coated black Kapton, beryllium copper, multilayer insulation, and solar cells) Cosmic dust particle impacts on spacecraft have been detected by electric field and plasma and radio wave instruments The accurate interpretation of these signals is complicated by many factors, including the details of the spacecraft antenna system, the local spacecraft plasma environment, and our understanding of the physics of the impact process The most basic quantity, the amount of charge liberated upon impact, is generally considered poorly constrained and is suspected to depend on the target material Here we show that for common materials used on spacecraft this variability is small for impacts around 10 km/s, and the impact charge yield can be approximated by 80 fC for a 1 pg projectile At higher speeds (∼50 km/s), variation of up to a factor of 5 is observed The measured yields in the 10–50 km/s range are compared to measurements and predictions from the literature and are found to be lower than predicted by at least a factor of 12 at 10 km/s and at least a factor of 17 at 50 km/s Impact charge is also found to depend on angle of incidence; the data suggest a maximum at 45°

Properties of dust particles near Saturn inferred from voltage pulses induced by dust impacts on Cassini spacecraft

Abstract: The Cassini Radio and Plasma Wave Science (RPWS) instrument can detect dust particles when voltage pulses induced by the dust impacts are observed in the wideband receiver. The size of the voltage pulse is proportional to the mass of the impacting dust particle. For the first time, the dust impacts signals measured by dipole and monopole electric antennas are compared, from which the effective impact area of the spacecraft is estimated to be 4 m2. In the monopole mode, the polarity of the dust impact signal is determined by the spacecraft potential and the location of the impact (on the spacecraft body or the antenna), which can be used to statistically infer the charge state of the spacecraft. It is shown that the differential number density of the dust particles near Saturn can be characterized as a power law dn/dr ∝ rμ, where μ ~ − 4 and r is the particle size. No peak is observed in the size distribution, contrary to the narrow size distribution found by previous studies. The RPWS cumulative dust density is compared with the Cosmic Dust Analyzer High Rate Detector measurement. The differences between the two instruments are within the range of uncertainty estimated for RPWS measurement. The RPWS onboard dust recorder and counter data are used to map the dust density and spacecraft charging state within Saturn's magnetosphere.

Development of the nano-dust analyzer (NDA) for detection and compositional analysis of nanometer-size dust particles originating in the inner heliosphere

Abstract: A linear time-of-flight mass spectrometer is developed for the detection and chemical analysis of nanometer-sized particles originating near the Sun. Nano-dust particles are thought to be produced by mutual collisions between interplanetary dust particles slowly spiraling toward the Sun and are accelerated outward to high velocities by interaction with the solar wind plasma. The WAVES instruments on the two STEREO spacecraft reported the detection, strong temporal variation, and potentially high flux of these particles. Here we report on the optimization and the results from the detailed characterization of the instrument's performance using submicrometer sized dust particles accelerated to 8–60 km/s. The Nano Dust Analyzer (NDA) concept is derived from previously developed detectors. It has a 200 cm2 effective target area and a mass resolution of approximately m/Δm = 50. The NDA instrument is designed to reliably detect and analyze nanometer-sized dust particles while being pointed close to the Sun's direction, from where they are expected to arrive. Measurements by such an instrument will determine the size-dependent flux of the nano-dust particles and its variations, it will characterize the composition of the nano-dust and, ultimately, it may determine their source. The flight version of the NDA instrument is estimated to be <5 kg and requires <10 W for operation.

SUDA: A Dust Mass Spectrometer for Compositional Surface Mapping for a Mission to Europa

Abstract: We developed a dust mass spectrometer to measure the composition of ballistic dust particles populating the thin exospheres that were detected around each of the Galilean moons. Since these grains are direct samples from the moons’ icy surfaces, unique composition data will be obtained that will help to define and constrain the geological activities on and below the moons? surface. The proposed instrument will make a vital contribution to NASA’s planned Europa Clipper mission and provide key answers to its main scientific questions about the surface composition, habitability, the icy crust, and exchange processes with the deeper interior of the Jovian icy moon Europa. The SUrface Dust Aanalyser (SUDA) is a time-offlight, reflectron-type impact mass spectrometer, optimised for a high mass resolution which only weakly depends on the impact location. The small size (268× 250×171 mm), low mass (< 4 kg) and large sensitive area (220 cm) makes the instrument well suited for the challenging demands of the Europa Clipper mission. A full-size prototype SUDA instrument was built in order to demonstrate its performance through calibration experiments at the dust accelerator at NASA’s IMPACT institute at Boulder, CO with a variety of cosmochemically relevant dust analogues. The effective mass resolution of m/∆m of 200-250 is achieved for mass range of interest m = 1-250. 1. Dust Exoclouds The basic idea of compositional mapping [1, 6] is that moons without an atmosphere are ensgulfed in clouds of dust particles released from their surfaces by meteoroid bombardment. The ejecta cloud particles can be detected and their composition analyzed from orbit or during a spacecraft flyby. The ejecta pro-duction process is very efficient: a typical interplanetary 10−8 kg micrometeoroid impact on a Jovian moon produces a large number of ejecta particles whith a total mass on the order of a few thousand times of that of the impactor [2]. These ejecta particles move on ballistic trajectories and most of them re-collide with the satellite due to the lower initial speed. As a consequence, an almost isotropic dust exosphere is present around the moon [3, 7]. In 1999, the Galileo dust instrument measured the density profiles of the tenuous dust exospheres around the Galilean satellites Callisto, Ganymede, and Europa [4]. The cloud density decreases asymptotically with radial distance as r−5/2, i.e. the cloud extent is only of a few moon radii. However, a spacecraft during a close flyby at Europa will detect a substantial number of ejecta particles. The initial speed of most ejecta particles is smaller than the escape velocity, which in turn is much smaller than the speed of an orbiting spacecraft. The ejecta particles thus hit the dust detector with the velocity of the spacecraft and arrive from the apex direction. The dynamic properties of the particles forming the ejecta cloud are unique and can be clearly distinguished from any other kind of cosmic dust likely to be detected in the vicinity of the satellite. 2. Instrument description The SUrface Dust Analyser (SUDA) is a reflectrontype, time-of-flight impact mass spectrometer, which has heritage from the Cassini CDA and the Stardust CIDA instruments. The main challenge for the design of a dust mass spectro-meter is to achieve simultaneously a high mass resolution, a sufficiently large sensitive area, and a compact design. The plasma ions produced by the hypervelocity impact may have a broad energy distributions of up to 100 eV, which limits the mass resolution of linear TOF dust spectrometer of reasonable size to about m/∆m = 50. The effect of EPSC Abstracts Vol. 9, EPSC2014-229, 2014 European Planetary Science Congress 2014 c © Author(s) 2014 EPSC European Planetary Science Congress Entrance Grid Signal Acceleration Grid Signal

The Interplanetary Meteoroid Environment for eXploration - (IMEX) project

Abstract: The 'Interplanetary Meteoroid Environment for eXploration' (IMEX) project, funded by the European Space Agency (ESA), aims to characterize dust trails and streams produced by comets in the inner solar system. We are therefore developing a meteoroid stream model that consists of a large database of cometary streams from all known comets in the inner solar system. This model will be able to predict meteor showers from most known comets, that can be observed anywhere in the inner solar system, at any time 1980-2080. This is relevant for investigating meteor showers on the Earth, on other planets, or at spacecraft locations. Such assessment of the dust impact hazard to spacecraft is particularly important in the context of human exploration of the solar system.

Dust in the Solar System

Abstract: Solar system dust is finely divided particulate matter that exists between the planets. These cosmic dust particles are also often called micrometeoroids and range in size from assemblages of a few molecules to tenth-millimeter-sized grains, above which size they are called meteoroids. Sources of this dust are larger meteoroids, comets, asteroids, the planets, and their moons and rings; there is interstellar dust sweeping through the solar system. Because of their small sizes, forces additional to solar and planetary gravity affect their trajectories. Radiation pressure and the interactions with ubiquitous magnetic fields disperse dust particles in space away from their sources. In this way, micrometeoroids become messengers of their parent bodies in distant regions of the solar system. A tablespoon of finely dispersed micrometer-sized dust grains scatters about 10 million times more light than a single meteoroid of the same mass. Therefore, a tiny amount of dust becomes recognizable, while the parent body from which it derived may remain undetected.