The Chemical Analyser subsystem of the Cosmic Dust Analyser (CDA) aboard the Cassini spacecraft performs in situ measurements of the chemical composition of dust in space. The instrument records ...time-of-flight mass spectra of cations, extracted from the impact cloud that is created by high-velocity particle impacts onto the detector target. Thus, the spectra not only show signals of particle components but also of ions from the target material and target contamination. The aim of this work is to determine which non-particle ions are to be expected in the spectra obtained in space operation at Saturn.
We present an analysis of the contamination state of the instrument's impact target. Beside investigations of the purity of the rhodium target surface, spectra from CDA calibration experiments at the dust accelerator facility are evaluated with regard to contamination signatures. Furthermore, contamination mass lines in spectra obtained by impacts of Jovian and Saturnian dust stream particles are analysed. Due to their small size and high speed, stream particle impacts predominantly produce ions from the target material and therefore the spectra are excellent probes of the contamination state of the target operating in space. With the exception of adsorbed hydrogen and carbon, the level of contamination is very low.
Implications for CDA spectra of Saturnian E ring particle impacts are derived. The findings confirm the published interpretations. The low level of alkali metal contamination implies a significant sodium contribution in the composition of E ring ice particles. Additionally, ionisation thresholds for the occurrence of contamination mass lines can be utilised to set limits for the impact velocity.
We present a method for producing metal-coated low-density (≲1600
kg
m
−3) aggregate silicate dust particles for use in hypervelocity impact (HVI) experiments. Particles fabricated using the method ...are shown to have charged and electrostatically accelerated in the Max Planck Institut für Kernphysik (MPI-K) 2
MV Van de Graaff accelerator, allowing the production of impact ionisation mass spectra of silicate particles (impacting at velocities ranging from <4 to >30
km
s
−1, corresponding to sizes of >1 to <0.1
μm) using the large area mass analyser (LAMA) instrument, designed for cosmic dust detection in space. Potential uses for the coated grains, such as in the calibration of aerogel targets similar to those used on the Stardust spacecraft, are also discussed.
Abstract
We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavours, and programmatic aspects that are important to maintain or develop ...in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an interstellar probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute – through measuring dust – to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it ‘rolls’ into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions.
Anorthite, the Ca‐rich end‐member of plagioclase feldspar, is a dominant mineral component of the Lunar highlands. Plagioclase feldspar is also found in comets, meteorites and stony asteroids. It is ...therefore expected to contribute to the population of interplanetary (and circumplanetary) dust grains within the solar system. After coating micron‐ and submicron‐sized grains of Anorthite with a conductive layer of Platinum, the mineral was successfully accelerated to hypervelocity speeds in the Max Planck Institut für Kernphysik's Van de Graaff accelerator. We present impact ionization mass spectra generated following the impacts of anorthite grains with a prototype mass spectrometer (the Large Area Mass Analyser, LAMA) designed for use in space, and discuss the behavior of the spectra with increasing impact energy. Correlation analysis is used to identify the compositions and sources of cations present in the spectra, enabling the identification of several molecular cations (e.g., CaAlO2, CaSiO2, Ca2AlO3/CaAlSi2O2) which identify anorthite as the progenitor bulk grain material.
Key Points
Laboratory simulation of cosmic dust impact ionization
Mass spectra of anorthite grains vary with impact velocity
Key spectral features are found which may identify the mineral
Stream particles are nanometer‐scale dust particles ejected with speeds ≳100 km s−1 from both the Jovian and Saturnian systems. Here we report the dynamical analysis of Saturnian stream particles on ...the basis of observations made by the Cosmic Dust Analyzer on board the Cassini spacecraft during its first three orbits around Saturn. The time span of the presented measurements covers from the beginning of orbit A to the end of orbit C (from the Saturn orbit insertion on 1 July 2004 UTC to 16 January 2005 UTC). During these orbits the Cassini spacecraft was usually located outside but not far from Saturn's magnetosphere. The Cassini observations therefore provide important information on the dynamics of stream particles just ejected from the system. As with earlier observations, two impact populations are identified. These appear as faint but continuous impacts as well as semiregular and energetic impact bursts. Faint impacts from directions close to the Saturn line of sight are recognized as recently ejected stream particles, while energetic dust bursts most probably consist of previously ejected particles that experienced significant acceleration within the solar wind. The presented measurements not only confirm the previous proposed stream particle ejection scenario but also serve as essential inputs for detailed dynamical modeling.
Key Points
Dust stream particle measurement at the vicinity of Saturn
New information about nanoparticle‐solar wind interaction
Semi‐periodic impact pattern
To understand the process of cosmic dust particle impacts and translate crater morphology on smoothed metallic surfaces to dust properties, correct calibration of the experimental impact data is ...needed. This article presents the results of studies of crater morphology generated by impacts using micron‐sized polypyrrole (PPy)‐coated olivine particles. The particles were accelerated by an electrostatic dust accelerator to high speeds before they impacted onto polished aluminum targets. The projectile diameter and velocity ranges were 0.3–1.2 μm and 3–7 km s−1. After impact, stereopair images of the craters were taken using scanning electron microscope and 3‐D reconstructions made to provide diameter and depth measurements. In this study, not just the dimensions of crater diameters and depths, but also the shape and dimensions of crater lips were analyzed. The craters created by the coated olivine projectiles are shown to have complicated shapes believed to be due to the nonspherical shape of the projectiles.
We present helium, argon, xenon and nitrogen isotopic data from Oceanic Island Basalts (OIBs), obtained from stepped heating and vacuum crushing experiments. Signatures of
3He/
4He in the present ...samples, except for those from the Canary Islands, are significantly higher (up to 20
×
the air ratio) than the MORB signature (8.5
×
air ratio). The argon (
40Ar/
36Ar) and xenon (
129Xe/
132Xe and
136Xe/
132Xe) isotopic data are consistent with a two-component mixture of gases from the mantle (either MORB or OIB source) and air contamination. In the stepwise heating data,
δ
15N varies from −
20‰ to +
15‰ in the different heating steps. The vacuum crushing data show a narrower range (−
5‰ to +
8‰) of
δ
15N, which, except for one Réunion sample, is somewhat heavier than the totals from the stepped heating experiments.
Simultaneous argon and nitrogen isotopic systematics of the present data suggest contributions from mantle (somewhat different from MORB), recycled materials and air contamination. This is also consistent with the
36Ar/
132Xe elemental ratio. The present stepped heating data are consistent with a nitrogen isotopic component with
δ
15N
~
−
25‰ in the OIB mantle. In line with the oxygen isotopic composition of the bulk Earth, this would be consistent with a contribution from enstatite chondrite-like volatiles to the planet's accretion.
We have performed infrared spectroscopy of meteoritic calcium-aluminum-rich inclusions (CAIs) from the CV chondrites Leoville and Allende. While some previous studies have focused on the wavelength ...range l < 25 km, we aimed at a detection and identification of CAI bands at wavelengths from 6 to 75 km. The resulting spectra have been compared with laboratory mineral spectra of typical CAI constituents such as melilite (a solid solution of gehlenite Ca sub(2)Al sub(2)SiO sub(7) and akermanite Ca sub(2)MgSi sub(2)0 sub(7)), spinel (MgAl sub(2)O sub(4)), diopside (CaMgSi sub(2)O sub(6)), and its Al- and Ti-rich variety fassaite. Sixteen bands in a type-B1 Leoville CAI transmittance spectrum could be assigned to melilite and spinel, 13 bands in the spectrum of a B3 Allende CAI were assigned to Al-Ti-diopside (fassaite), spinel, and nepheline; both cases were in accordance with the sample's respective mineralogical and chemical composition. CaO (lime) is not detected spectroscopically in the CAI spectra, as it is (contrary to previous notions) not even a trace component in CAIs, at least in their present (partially reprocessed) state. The astrophysical relevance of our study lies in the fact that the main CAI minerals such as melilite, Al-Ti-diopside (fassaite), spinel, and anorthite are expected to be present in protoplanetary disks. Hence, the detection of Ca, Al-minerals in protoplanetary disks should only be a matter of increased instrumental sensitivity, or spatial and spectral resolution, and quality (e.g., wavelength coverage) of comparative laboratory spectra.
The processes of alteration of airless bodies exposed to the space environment are referred to be as “space weathering.” Multiple agents contribute generally to space weathering, to an extent that ...depends on the specific location of the surface within the solar system. Typical space weathering agents encountered in the solar system are solar radiation, solar wind and cosmic rays, magnetospheric plasma (e.g., at Jupiter or Saturn), and cosmic dust. The effect of space weathering is generally assessed by measuring the surfaces optical properties, for example, by near‐infrared spectroscopy. The alteration of the surfaces is due to a cumulative effect over time of all agents. We investigate in this paper the contribution of micrometeoroid (dust) bombardment on different asteroids, by using the Interplanetary Micrometeoroid Environment Model for the interplanetary dust populations and a simplified model of interstellar dust dynamics. We quantify, for different representative asteroids (main belt and Near Earth Objects NEOs), the particle cumulative flux, mass flux, impact velocity, and the kinetic impact energy deposited. This work is primarily intended to support laboratory work investigating the effect of energy deposition onto sample surfaces, as well as astronomical observations of optical properties of asteroid surfaces.
Plain Language Summary
This paper explores the impact speed, mass flux, and kinetic energy flux of interplanetary and interstellar micrometeoroids on near‐earth and main belt asteroids from different dynamical families. This paper aims at providing constraints to current and future experimental work to understand the space weathering of asteroids surfaces induced by dust impacts.The simulations are performed using the latest version of the micrometeoroid environment model of the European Space Agency (Interplanetary Micrometeoroid Environment Model). We find that for all asteroids studied, the dust impactors deposit orders of magnitude less energy on the asteroid surfaces compared to the solar radiations but their contribution is comparable to that of heavy solar wind ions and electrons. We find that large cometary grains provide most of the mass flux delivered to asteroids surfaces, independently of the asteroids orbital elements, suggesting that dust bombardment is unlikely to play a significant role in driving the observed spectral trends among the different asteroids. While surface gardening by dust bombardment may, in turn, expose fresh material from the asteroid's surface, the required interplanetary dust population mass flux seems too low to efficiently counterbalance the surface weathering due to solar wind implantation.
Key Points
This paper presents the modeling of micrometeoroid impacts on main belt and near-Earth asteroids
The contribution of cometary, asteroidal, and interstellar dust as space weathering agents is evaluated
— Noble gas data from Martian meteorites have provided key constraints about their origin and evolution, and their parent body. These meteorites have witnessed varying shock metamorphic overprinting ...(at least 5 to 14 GPa for the nakhlites and up to 45–55 GPa (e.g., the lherzolitic shergottite Allan Hills ALH A77005), solar heating, cosmic‐ray exposure, and weathering both on Mars and Earth. Influences on the helium budgets of Martian meteorites were evaluated by using a new data set and literature data. Concentrations of 3He, 4He, U, and Th are measured and shock pressures for same sample aliquots of 13 Martian meteorites were determined to asses a possible relationship between shock pressure and helium concentration. Partitioning of 4He into cosmogenic and radiogenic components was performed using the lowest 4He/3He ratio we measured on mineral separates (4He/3He = 4.1, pyroxene of ALHA77005). Our study revealed significant losses of radiogenic 4He. Systematics of cosmogenic 3He and neon led to the conclusion that solar radiation heating during transfer from Mars to Earth and terrestrial weathering can be ruled out as major causes of the observed losses of radiogenic helium in bulk meteorites. For bulk rock we observed a correlation of shock pressure and radiogenic 4He loss, ranging between ˜20% for Chassigny and other moderately shocked Martian meteorites up to total loss for meteorites shocked above 40 GPa. A steep increase of loss occurs around 30 GPa, the pressure at which plagioclase transforms to maskelynite. This correlation suggests significant 4He loss induced by shock metamorphism. Noble gas loss in rocks is seen as diffusion due to (1) the temperature increase during shock loading (shock temperature) and (2) the remaining waste heat after adiabatic unloading (post shock temperature). Modeling of 4He diffusion in the main U, Th carrier phase apatite showed that post‐shock temperatures of ˜300 °C are necessary to explain observed losses. This temperature corresponds to the post‐shock temperature calculated for bulk rocks shocked at about 40 GPa. From our investigation, data survey, and modeling, we conclude that the shock event during launch of the meteorites is the principal cause for 4He loss.
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