Showing papers by "Eberhard Grün published in 2002"

Origins of Solar System Dust beyond Jupiter

Abstract: The measurements of cosmic interplanetary dust by the instruments on board the Pioneer 10 and 11 spacecraft contain the dynamical signature of dust generated by Edgeworth-Kuiper belt objects, as well as short-period Oort cloud comets and short-period Jupiter-family comets. While the dust concentration detected between Jupiter and Saturn is mainly due to the cometary components, the dust outside Saturn's orbit is dominated by grains originating from the Edgeworth-Kuiper belt. In order to sustain a dust concentration that accounts for the Pioneer measurements, short-period external Jupiter-family comets, on orbits similar to that of comet 29P/Schwassmann-Wachmann 1, have to produce 8 × 104 g s-1 of dust grains with sizes between 0.01 and 6 mm. A sustained production rate of 3 × 105 g s-1 has to be provided by short-period Oort cloud comets on 1P/Halley-like orbits. The comets cannot, however, account for the dust flux measured outside Saturn's orbit. The measurements there can only be explained by generation of dust grains in the Edgeworth-Kuiper belt by mutual collisions of the source objects and by impacts of interstellar dust grains onto the objects' surfaces. These processes have to release in total 5 × 107 g s-1 of dust from the Edgeworth-Kuiper belt objects in order to account for the amount of dust found by Pioneer beyond Saturn, making the Edgeworth-Kuiper disk the brightest extended feature of the solar system when observed from afar.

A tenuous dust ring of Jupiter formed by escaping ejecta from the Galilean satellites

Abstract: [1] This paper focuses on the dust environment between the orbits of the Galilean moons of Jupiter Recent discovery of dust clouds around the Galilean satellites formed by impact ejecta from hypervelocity impacts of interplanetary micrometeoroids [Kruger et al, 1999d] suggests that a fraction of the ejected particles may escape from the source satellites into circum-Jovian orbits We estimate production rates and study dynamical evolution of the escaping ejecta, controlled by gravitational, radiation pressure, and electromagnetic forces, to show that grains larger than several tenths of a micrometer in radius are likely to stay in bound orbits around Jupiter for tens or hundreds of years until they either are lost to collisions with the satellites or Jupiter or are ejected to interplanetary space It is concluded that these small debris form a broad dust ring with number densities up to ∼103 km−3, extending at least from Europa's orbit outward beyond the orbit of Callisto Our results are consistent with in situ measurements of the Galileo spacecraft We analyze impact events recorded by the Galileo dust detector from 1996 through 2001 and find more than 200 events outside the orbit of Europa, compatible with impacts of particles orbiting Jupiter in prograde orbits An empirical dust number density distribution derived from these data agrees quite well with the theoretical one

New information recovered from the Pioneer 11 meteoroid experiment data

Abstract: Data of the Pioneer 11 meteoroid experiment are re-evaluated. A probabilistic model of the dust detector is constructed with no assumption on the flux of particles, using built-in redundancy of the instrument only. The analysis of redundant data strongly suggests that the instrument had suffered a failure at launch that disabled a significant part of its impact sensors. This failure reduced the total sensitive area of the detector, and the fluxes derived earlier assuming the instrument was in good health underestimated the true fluxes. We apply our model to re-derive the true particle fluxes, taking now the reduction of the initial sensor number into account. We implement a kind of in-flight calibration of a dust detector in natural meteoroid environment. We end up with higher true fluxes and wider confidence intervals that represent the best knowledge of the instrument's in-flight characteristics.

Dust en-route to jupiter and the galilean satellites

Abstract: Spacecraft investigations during the last ten years have vastly improved our knowledge about dust in the Jovian system. All Galilean satellites, and probably all smaller satellites as well, are sources of dust in the Jovian system. In-situ measurements with the dust detectors on board the Ulysses and Galileo spacecraft have for the first time demonstrated the electromagnetic interaction of charged dust grains with the interplaetary magnetic field and with a planetary magnetosphere. Jupiter's magnetosphere acts as a giant mass-velocity spectrometer for charged 10-nanometer dust grains. These dust grains are released from Jupiter's moon Io with typical rate of ≈ 1 kg s − . The dust streams probe the plasma conditions in the Io plasma torus and can be used as a potential monitor of Io's volcanic plume activity. The other Galilean satellites are surrounded by tenuous impact-generated clouds of mostly sub-micrometer ejecta grains. Galileo measurements have demonstrated that impact-ejecta derived from hypervelocity impacts onto satellites are the major—if not the only—constituent of dusty planetary rings. We review the in-situ dust measurements at Jupiter and give an update of most recent results.

Io revealed in the Jovian dust streams

Abstract: The Jovian dust streams are high-speed bursts of submicron-sized particles traveling in the same direction from a source in the Jovian system. Since their discovery in 1992, they have been observed by three spacecraft: Ulysses, Galileo and Cassini. The source of the Jovian dust streams is dust from Io's volcanoes. The charged and traveling dust stream particles have particular signatures in frequency space and in real space. The frequency-transformed Galileo dust stream measurements show different signatures, varying orbit-to-orbit during Galileo's first 29 orbits around Jupiter. Time-frequency analysis demonstrates that Io is a localized source of charged dust particles. Aspects of the particles' dynamics can be seen in the December-2000 joint Galileo-Cassini dust stream measurements. To match the travel times, the smallest dust particles could have the following range of parameters: radius: 6nm, density: 1.35-1.75gr/cm$^3$, sulfur charging conditions, which produce dust stream speeds: 220|450km/sec (Galileo|Cassini) and charge potentials: 5.5|6.3Volt (Galileo|Cassini).

Charging Processes for Dust Particles in Saturn's Magnetosphere

Abstract: We investigated the electrostatic charging behavior of submillimeter-sized dust particleslocated in Saturn's magnetosphere. The charging effects we considered included electron/ion capture from the magnetospheric plasma, electron/ion capture from the solarwind plasma, the photoelectric effect from solar radiation, and secondary electron emission from energetic electrons. In our results we show charging times and equilibrium charges for particles located in different regions of Saturn's magnetosphere. We find that charging in Saturn's magnetosphere is not particularly sensitive to the dust particle's material properties. The equipotential ranges from ∼−2 V at 3.5 R S , decreasing to ∼−5 V at 6 R S , and then increasing to ∼−1.5V at 10 R S . The charging time for one micron-sized particles is a few minutes, and for 0.01 micron-sized particles the charging time is 6 hours (or more). The latter is a significant fraction of Saturn's rotation period.

Charging processes for dust particles in Saturn's magnetosphere

Abstract: We investigated the electrostatic charging behavior of submillimeter-sized dust particles located in Saturn's magnetosphere. The charging effects we considered included electron/ion capture from the magnetospheric plasma, electron/ion capture from the solar-wind plasma, the photoelectric effect from solar radiation, and secondary electron emission from energetic electrons. In our results, we show charging times and equilibrium potentials for particles located in different regions of Saturn's magnetosphere. We find that charging in Saturn's magnetosphere is not particularly sensitive to the dust particle's material properties. The equipotential ranges from $\sim$-2 V at 3.5 R$_S$, decreasing to $\sim$-5 V at 6 R$_S$, and then increasing to $\sim$-1.5 V at 10 R$_S$. The charging time for micron-sized particles is a few minutes, and for 0.01 micron-sized particles the charging time is 6 hours (or more). The latter is a significant fraction of Saturn's rotation period.

A new dust source for the Heidelberg dust accelerator

Abstract: The Max-Planck-Institut fur Kernphysik in Heidelberg owns a dust accelerator, whichis able to provide micron and submicron sized particles with speeds between 1 and 80 km s −1 . The type of dust materials and the speed and mass range of the accelerated particles is dependent on the design of the dust reservoir at the front end of the accelerator beam line. In order to improve the capabilities of this reservoir, a new dust source was developed. A simplification in the source design allows a more efficient particle extraction. Also new sorts of dust can now be accelerated at the Heidelberg facilities: Iron, silver, copper, carbon and latex. This paper describes the dust source and the properties of the first accelerated dust samples. The experiments were performed at both, the 20 kV test bench and the 2 MV accelerator.

CDA cruise science: Comparison of measured dust flux at 1 AU with models

Abstract: The data gathered by the Cosmic Dust Analyser (CDA) on board Cassini close to 1 AU are investigated To compare the measured flux with models, the sensitivity of the targets is derived from calibration data The interplanetary model by Staubach [1] underestimates the measured flux by more than one order of magnitude Our attempt to classify the measured events as impacts on the large and the small target, indiates that there are impacts on the side walls which lead to measurable signals on the targets This brings the measured flux closer to the model, but cannot explain the large discrepancy It is shown that interstellar particles could fill the gap between the interplanetary flux model and the measured impact rate

Dust telescope: A new tool for dust research

Abstract: Dust particles in space carry information about their birth at a remote site in space and time not accessible to direct investigation. When we know where dust particles come from, we can derive from their state and composition important knowledge about the processes by which they were formed. This information can be gained by a combination of trajectory analysis together with the physical and chemical analysis of dust particles. Potential targets of a dust telescope can be interstellar dust phenomena (e.g. local interstellar medium or dusty stellar systems like beta-Pictoris), interplanetary phenomena (e.g. meteor stream dust, cometary, or asteroidal dust, or dust from the moon), or even space debris (e.g. fine grains from solid rocket burns). It is proposed to use a 1 m 2 dust telescope with 50° aperture. Such an instrument would detect 5 and 0.5 interplanetary dust grains of 10 −15 g and 10 −12 g per day, respectively. A state-of-the-art dust telescope consists of an array of parallel mounted dust analyzers. Potential components are a high resolution impact mass spectrometer, a dust analyzer for the determination of physical and chemical dust properties, a dust momentum sensor, and a large-area impact detector with trajectory analysis. A first example of such a dust telescope is carried by the proposed Galactic DUNE mission. The goal of DUNE is the analysis of interstellar grains near Earth.

Mars Dust Counter (MDC) on board NOZOMI: Initial results

Abstract: Mars Dust Counter (MDC) is a light-weight (730g) impact-ionization dust detector onboard NOZOMI, a Japanese Mars mission, which was launched on July 4th 1998. The main aim of MDC is to detect the predicted Martian dust rings/tori. It can also cover velocitymass ranges of interplanetary and interstellar dust particles. By August 2000, MDC had detected more than 60 dust particles. In 1999, it detected five fast particles probably of interstellar origin. For five years from 1999 to 2003, NOZOMI will orbit the sun and MDC can measure interplanetary and interstellar dust between the Earth's and Mars' orbits.

Application of new, low density projectiles to the laboratory calibration of the Cassini Cosmic Dust Analyser (CDA)

Abstract: The Cassini Dust Analyser (CDA) has the capacity to provide composition informationfrom impacting micrometeoroids through impact ionization, time-of-flight mass spectrometry. The instrument, aboard the Cassini-Huygens mission, has been collecting data since March 1999 during its journey to the Saturnian system (2004) via Jupiter (December 2000). The University of Kent at Canterbury is using A 2-MV Van de Graaff electrostatic accelerator and laboratory CDA model to perform a calibration programme primarily focused upon the Chemical Analyser. The particles used to simulate impacts and characterise the instrument responses are of the same velocity (up to 37 km s −1 ) and mass (10 −19 –10 −15 kg) as those expected from interplanetary space. A variety of materils are used although of particular interest are revolutionary low-density, coated-latex particles. They enable complex organic spectra to be obtained under laboratory conditions. The suitability of these particles for the calibration of CDA type instruments and the current status of the ongoing programme to investigate the system's response are reported.