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50 result(s) for "Grün, Eberhard"
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The Dawn of Dust Astronomy
We review the development of dust science from the first ground-based astronomical observations of dust in space to compositional analysis of individual dust particles and their source objects. A multitude of observational techniques is available for the scientific study of space dust: from meteors and interplanetary dust particles collected in the upper atmosphere to dust analyzed in situ or returned to Earth. In situ dust detectors have been developed from simple dust impact detectors determining the dust hazard in Earth orbit to dust telescopes capable of providing compositional analysis and accurate trajectory determination of individual dust particles in space. The concept of Dust Astronomy has been developed, recognizing that dust particles, like photons, carry information from remote sites in space and time. From knowledge of the dust particles’ birthplace and their bulk properties, we learn about the remote environment out of which the particles were formed. Dust Observatory missions like Cassini, Stardust, and Rosetta study Saturn’s satellites and rings and the dust environments of comet Wild 2 and comet Churyumov-Gerasimenko, respectively. Supplemented by simulations of dusty processes in the laboratory we are beginning to understand the dusty environments in space.
High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko
The COSIMA mass spectrometer on the Rosetta spacecraft has analysed the solid organic matter found in dust particles emitted by comet 67P/Churyumov–Gerasimenko; this matter is similar to the insoluble organic matter extracted from carbonaceous chondrites such as the Murchison meteorite, but is perhaps more primitive. Organic matter on comet 67P The COSIMA mass spectrometer on board the ESA Rosetta spacecraft has detected more than 27,000 particles in the vicinity of comet 67P/Churyumov–Gerasimenko. Of these, more than 200 particles have been analysed so far and this paper presents further chemical analysis of two of these particles, dubbed Kenneth and Juliette. The results reveal the presence of solid organic matter, in which the carbon is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The authors conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but has suffered less modification before and/or after incorporation in the comet. The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley 1 , 2 . Such matter is generally thought to have originated in the interstellar medium 3 , but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed 4 . This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization 5 . Many gaseous organic molecules, however, have been observed 6 , 7 , 8 , 9 ; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei 8 . These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula 10 . Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites 11 , 12 . The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies 11 . We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
Mercury Dust Monitor (MDM) Onboard the Mio Orbiter of the BepiColombo Mission
An in-situ cosmic-dust instrument called the Mercury Dust Monitor (MDM) had been developed as a part of the science payload for the Mio (Mercury Magnetospheric Orbiter, MMO) stage of the joint European Space Agency (ESA)–JAXA Mercury-exploration mission. The BepiColombo spacecraft was successfully launched by an Ariane 5 rocket on October 20, 2018, and commissioning tests of the science payload were successfully completed in near-earth orbit before injection into a long journey to Mercury. MDM has a sensor consisting of four plates of piezoelectric lead zirconate titanate (PZT), which converts the mechanical stress (or strain) induced by dust-particle impacts into electrical signals. After the commencement of scientific operations, MDM will measure the impact momentum at which dust particles in orbit around the Sun collide with the sensor and record the arrival direction. This paper provides basic information concerning the MDM instrument and its predicted scientific operation as a future reference for scientific articles concerning the MDM’s observational data.
Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft
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.
Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring
During Cassini's close flyby of Enceladus on 14 July 2005, the High Rate Detector of the Cosmic Dust Analyzer registered micron-sized dust particles enveloping this satellite. The dust impact rate peaked about 1 minute before the closest approach of the spacecraft to the moon. This asymmetric signature is consistent with a locally enhanced dust production in the south polar region of Enceladus. Other Cassini experiments revealed evidence for geophysical activities near Enceladus' south pole: a high surface temperature and a release of water gas. Production or release of dust particles related to these processes may provide the dominant source of Saturn's E ring.
Modelling cometary meteoroid stream traverses of the Martian Moons eXploration (MMX) spacecraft en route to Phobos
The Martian Moons Exploration (MMX) spacecraft is a JAXA mission to Mars and its moons Phobos and Deimos. MMX will be equipped with the Circum-Martian Dust Monitor (CMDM) which is a newly developed light-weight (650g) large area (1m2) dust impact detector. Cometary meteoroid streams (also referred to as trails) exist along the orbits of comets, forming fine structures of the interplanetary dust cloud. The streams consist predominantly of the largest cometary particles (with sizes of approximately 100μm to 1 cm) which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new and recently published universal model for cometary meteoroid streams in the inner Solar System. We use IMEX to study the detection conditions of cometary dust stream particles with CMDM during the MMX mission in the time period 2024 to 2028. The model predicts traverses of 12 cometary meteoroid streams with fluxes of 100μm and bigger particles of at least 10-3m-2day-1 during a total time period of approximately 90 days. The highest flux of 0.15m-2day-1 is predicted for comet 114P/Wiseman-Skiff in October 2026. With its large detection area and high sensitivity CMDM will be able to detect cometary meteoroid streams en route to Phobos. Our simulation results for the Mars orbital phase of MMX also predict the occurrence of meteor showers in the Martian atmosphere which may be observable from the Martian surface with cameras on board landers or rovers. Finally, the IMEX model can be used to study the impact hazards imposed by meteoroid impacts onto large-area spacecraft structures that will be particularly necessary for crewed deep space missions.
Dust Environment Modelling of Comet 67P/Churyumov-Gerasimenko
Dust is an important constituent of cometary emission; its analysis is one of the major objectives of ESA's Rosetta mission to comet 67P/Churyumov-Gerasimenko (C-G). Several instruments aboard Rosetta are dedicated to studying various aspects of dust in the cometary coma, all of which require a certain level of exposure to dust to achieve their goals. At the same time, impacts of dust particles can constitute a hazard to the spacecraft. To conciliate the demands of dust collection instruments and spacecraft safety, it is desirable to assess the dust environment in the coma even before the arrival of Rosetta. We describe the present status of modelling the dust coma of 67P/C-G and predict the speed and flux of dust in the coma, the dust fluence on a spacecraft along sample trajectories, and the radiation environment in the coma. The model will need to be refined when more details of the coma are revealed by observations. An overview of astronomical observations of 67P/C-G is given, because model parameters are derived from this data if possible. For quantities not yet measured for 67P/C-G, we use values obtained for other comets, e.g. concerning the optical and compositional properties of the dust grains. One of the most important and most controversial parameters is the dust mass distribution. We summarise the mass distribution functions derived from the in-situ measurements at comet 1P/Halley in 1986. For 67P/C-G, constraining the mass distribution is currently only possible by the analysis of astronomical images. We find that both the dust mass distribution and the time dependence of the dust production rate of 67P/C-G are those of a fairly typical comet.
Constraints on dust production in the Edgeworth-Kuiper Belt from Pioneer 10 and New Horizons measurements
Impact ejecta and collisional debris from the Edgeworth‐Kuiper Belt are the dominant source of micron‐sized grains in the outer solar system, as they slowly migrate inwards through the outer solar system before most grains are ejected during close encounters with Jupiter. These grains drive several phenomena in the outer solar system, including the generation of impact ejecta clouds at airless bodies, the formation of ionospheric layers and neutral gases in the atmospheres of the giant planets due to meteoric ablation, the generation of tenuous outer planetary ring systems and the spatial and compositional alteration of Saturn's main rings. Previous analyses have offered estimates of the net mass production rate from the Edgeworth‐Kuiper Belt both theoretically and observationally. In order to improve upon these estimates, we compare measurements of the interplanetary dust density in the outer solar system by both the Pioneer 10 meteoroid detector and the New Horizons Student Dust Counter with a dynamical dust grain tracing model. Our best estimates for the net mass production rate and the ejecta mass distribution power law exponent are (8.9 ± 0.5) × 105 g/s and 3.02 ± 0.04, respectively. Key Points Dust grains produced in the Kuiper Belt migrate inward Dynamical dust grain tracing code is used to establish relative dust densities Measurements by Pioneer 10 and New Horizons constrain dust production rates
SUDA: A SUrface Dust Analyser for Compositional Mapping of the Galilean Moon Europa
The Surface Dust Analyser (SUDA) is a mass spectrometer onboard the Europa Clipper mission for investigating the surface composition of the Galilean moon Europa. Atmosphereless planetary moons such as the Galilean satellites are wrapped into a ballistic dust exosphere populated by tiny samples from the moon’s surface produced by impacts of fast micrometeoroids. SUDA will measure the composition of such surface ejecta during close flybys of Europa to obtain key chemical signatures for revealing the satellite’s composition such as organic molecules and salts, history, and geological evolution. Because of their ballistic orbits, detected ejecta can be traced back to the surface with a spatial resolution roughly equal to the instantaneous altitude of the spacecraft. SUDA is a Time-Of-Flight (TOF), reflectron-type impact mass spectrometer, optimized for a high mass resolution which only weakly depends on the impact location. The instrument will measure the mass, speed, charge, elemental, molecular, and isotopic composition of impacting grains. The instrument’s small size of 268 mm × 250 mm × 171 mm , radiation-hard design, and rather large sensitive area of 220 cm 2 matches well the challenging demands of the Clipper mission.
Composition of Saturnian Stream Particles
During Cassini's approach to Saturn, the Cosmic Dust Analyser (CDA) discovered streams of tiny (less than 20 nanometers) high-velocity ([approximately]100 kilometers per second) dust particles escaping from the saturnian system. A fraction of these impactors originated from the outskirts of Saturn's dense A ring. The CDA time-of-flight mass spectrometer recorded 584 mass spectra from the stream particles. The particles consist predominantly of oxygen, silicon, and iron, with some evidence of water ice, ammonium, and perhaps carbon. The stream particles primarily consist of silicate materials, and this implies that the particles are impurities from the icy ring material rather than the ice particles themselves.