Combined noble gas and trace element measurements on individual stratospheric interplanetary dust particles

Abstract— The trace element compositions and noble gas contents of 32 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were measured. Trace element compositions are generally similar to CI meteorites, with occasional depletions in Zn/Fe with respect to CI. Noble gases were detected in all but one of the IDPs. Noble gas elemental compositions are consistent with the presence of fractionated solar wind. A rough correlation between surface‐normalized He abundances and Zn/Fe ratios is observed; Zn‐poor particles generally have lower He contents than the other IDPs. This suggests that both elements were lost by frictional heating during atmospheric entry and confirms the view that Zn can serve as an entry‐heating indicator in IDPs.     

Extraction of helium from individual interplanetary dust particles by step-heating

Abstract Fragments from 20 individual particles, collected in the Earth's stratosphere and believed to be interplanetary dust particles (IDPs), were obtained from NASA's Johnson Space Center collection and subjected to step-heating to see if differences in the release pattern for ⁴He could be observed which might provide clues to the origin of the particles. Comparisons were made to the release pattern for 18 individual lunar surface grains heated in the same manner. Twelve of the IDP fragments contained an appreciable amount of ⁴He, 50 percent of which was released by the time the particles were heated to approximately 630 °C. For the 18 individual lunar grains the corresponding average temperature was 660 °C. The ³He/⁴He ratios found for these fragments agreed well with those found for deep Pacific magnetic fines believed to be of extraterrestrial origin, and were comparable to those which have been observed for the solar wind and lunar surface soil grains. Four of the IDP fragments contained appreciably less ⁴He, and this was released at a higher temperature. The remaining four fragments had too little ⁴He to permit a determination. From Flynn's analyses of the problem of the heating of IDPs in their descent in the atmosphere, the present results suggest that the parent IDPs of the 12 particles which contained an appreciable amount of ⁴He suffered very little heating in their descent and are likely of asteroidal origin, although one cannot rule out the possibility that at least some of them had a cometary origin and entered the earth's atmosphere at a grazing angle. Mineralogical and morphological studies on fragments companion to those used in the present investigation are under way. When these are completed, a more definite picture should emerge.     

Reflectance spectroscopy of interplanetary dust particles

Abstract Reflectance spectra were collected from chondritic interplanetary dust particles (IDPs), a polar micrometeorite, Allende (CV3) meteorite matrix, and mineral standards using a microscope spectrophotometer. Data were acquired over the 380–1100 nm wavelength range in darkfield mode using a halogen light source, particle aperturing diaphrams, and photomultiplier tube (PMT) detectors. Spectra collected from titanium oxide (Ti₄O₇), magnetite (Fe₃O₄), and Allende matrix establish that it is possible to measure indigenous reflectivities of micrometer-sized (>5 μm in diameter) particles over the visible (VIS) wavelength range 450–800 nm. Below 450 nm, small particle effects cause a fall-off in signal into the ultraviolet (UV). Near-infrared (IR) spectra collected from olivine and pyroxene standards suggest that the ～1 μm absorption features of Fe-bearing silicates in IDPs can be detected using microscope spectrophotometry. Chondritic IDPs are dark objects (<15% reflectivity) over the VIS 450–800 nm range. Large (>1 μm in diameter) embedded and adhering single mineral grains make IDPs significantly brighter, while surficial magnetite formed by frictional heating during atmospheric entry makes them darker. Most chondritic smooth (CS) IDPs, dominated by hydrated layer silicates, exhibit generally flat spectra with slight fall-off towards 800 nm, which is similar to type CI and CM meteorites and main-belt C-type asteroids. Most chondritic porous (CP) IDPs, dominated by anhydrous silicates (pyroxene and olivine), exhibit generally flat spectra with a slight rise towards 800 nm, which is similar to outer P and D asteroids. The most C-rich CP IDPs rise steeply towards 800 nm with a redness comparable to that of the outer asteroid object Pholus (Binzel, 1992). Chondritic porous IDPs are the first identified class of meteoritic materials exhibiting spectral reflectivities (between 450 and 800 nm) similar to those of P and D asteroids. Although large mineral grains, secondary magnetite, and small particle effects complicate interpretation of IDP reflectance spectra, microscope spectrophotometry appears to offer a rapid, nondestructive technique for probing the mineralogy of IDPs, comparing them with meteorites, investigating their parent body origins, and identifying IDPs that may have been strongly heated during atmospheric entry.     

The electric potential on dust particles in comets and in interplanetary space

We calculate the electric surface potential reached by small dust particles in cometary atmospheres and in interplanetary space. Plasma temperature and density are varied over a wide range; a two component plasma of ions and electrons in thermodynamic equilibrium is assumed. The calculations are performed for three types of grains whose photoelectric and secondary electron emission yield are choosen to cover about the range expected for real dust. Results for vanishing secondary electron emission are given for comparison. At the beginning, a short review of the theoretical formulation and the main assumptions are presented. Wir berechnen das Oberflächenpotential kleiner Staubteilchen im Plasma einer Kometenatmosphäre und im interplanetaren Raum. Die Plasma-parameter Temperatur und Dichte werden in einem weiten Bereich variiert, es wird jedoch stets thermodynamisches Gleichgewicht zwischen Elektronen und Ionen eines Zweikomponentenplasmas angenommen. Die Rechnungen werden für drei Teilchenmaterialien ausgeführt, deren Photo-effekt und Sekundärelektronenausbeute etwa den an realen Staubteilchen vorkommenden Bereich überdecken dürften; zum Vergleich werden auch die Ergebnisse bei vernachlässigbarer Sekundärelektronenausbeute mitgeteilt. Eine kurze Zusammenfassung der theoretischen Grundlagen und der wesentlichen Voraussetzungen ist den Rechnungen vorangestellt.     

Noble gases in interplanetary dust particles,I: The excess helium‐3 problem and estimates of the relative fluxes of solar wind and solar energetic particles in interplanetary space

Abstract— We report mass‐spectrometric measurements of light noble gases pyrolytically extracted from 28 interplanetary dust particles (IDPs) and discuss these new data in the context of earlier analyses of 44 IDPs at the University of Minnesota. The noble gas database for IDPs is still very sparse, especially given their wide mineralogic and chemical variability, but two intriguing differences from isotopic distributions observed in lunar and meteoritic regolith grains are already apparent. First are puzzling overabundances of ³He, manifested as often strikingly elevated ³He/⁴He ratios—up to >40x the solar‐wind value—‐and found primarily but not exclusively in shards of some of the larger IDPs (“cluster particles”) that fragmented on impact with the collectors carried by high‐altitude aircraft. It is difficult to attribute these high ratios to ³He production by cosmic‐ray‐induced spallation during estimated space residence times of IDPs, or by direct implantation of solar‐flare He. Minimum exposure ages inferred from the ³He excesses range from ～50 Ma to an impossible >10 Ga, compared to Poynting‐Robertson drag lifetimes for low‐density 20–30 μm particles on the order of ～0.1 Ma for an asteroidal source and ～10 Ma for origin in the Kuiper belt. The second difference is a dominant contribution of solar‐energetic‐particle (SEP) gases, to the virtual exclusion of solar‐wind (SW) components, in several particles scattered throughout the various datasets but most clearly and consistently observed in recent measurements of a group of individual and cluster IDPs from three different collectors. Values of the SEP/SW fluence ratio in interplanetary space from a simple model utilizing these data are ～1% of the relative SEP/SW abundances observed in lunar regolith grains, but still factors of approximately 10–100 above estimates for this ratio in low‐energy solar particle emission.     

Upper limit concentrations of trapped xenon in individual interplanetary dust particles from the stratosphere

Abstract— The Xe contents in 25 individual stratospheric interplanetary dust particles were measured in two different laboratories using focused laser micro‐gas extraction and (1) a conventional low‐blank magnetic sector mass spectrometer (Washington University), and (2) a resonance ionization time of flight mass spectrometer (RELAX‐University of Manchester). Data from both laboratories yielded a remarkably similar upper‐limit ¹³²Xe concentration in the IDPs (>2.7, 6.8 and 2.2 × 10^?8ccSTP/g for Washington University Run 1, Washington University Run 2 and University of Manchester analyses, respectively), which is up to a factor of five smaller than previous estimates. The upper‐limit ¹³²Xe/³⁶Ar ratio in the IDPs (¹³²Xe/³⁶Ar > ?8 × 10^?4for Run 1 and ¹³²Xe/³⁶Ar > ?19 × 10^?4for Run 2), computed using ³⁶Ar concentration data reported elsewhere is consistent with a mixture between implanted solar wind, primordial, and atmospheric noble gases. Most significantly, there is no evidence that IDPs are particularly enriched in primordial noble gases compared to chondritic meteorites, as implied by previous work.     

The elemental abundances in interplanetary dust particles

Abstract— We compiled a table of all major, minor, and trace-element abundances in 89 interplanetary dust particles (IDPs) that includes data obtained with proton-induced x-ray emission (PIXE), synchroton x-ray fluorescence (SXRF), and secondary ion mass spectrometry (SIMS). For the first time, the reliability of the trace-element abundances in IDPs is tested by various crosschecks. We also report on the results of cluster analyses that we performed on IDP compositions. Because of the incompleteness of the data set, we included only the elements Cr, Mn, Ni, Cu, and Zn, normalized to Fe and CI chondrite abundances, that are determined in 73 IDPs. The data arrange themselves in four rather poorly defined groups that we discuss in relation to CI chondrites following the assumption that on the average CI abundances are most probable. The largest group (chondritic), with 44 members, has close to CI abundances for many refractory and moderately refractory elements (Na, Al, Si, P, K, Sc, Ti, V, Cr, Co, Ge, Sr). It is slightly depleted in Fe and more in Ca and S, while the volatile elements (Cl, Cu, Zn, Ga, Se, Rb) are enriched by =1.7 × CI and Br by 21 × CI. The low-Zn group, with 12 members, is very similar to the chondritic group except for its Zn-depletion, stronger Ca-depletion and Fe-enrichment. The low-Ni group, with 11 members, has Ni/Fe = 0.03 × CI and almost CI-like Ca, but its extraterrestrial origin is not established. The last group (6 members) contains non-systematic particles of unknown origin. We found that Fe is inhomogeneously distributed on a micron scale. Furthermore, the abundances of elements that are measured near their limits of detection are easily overestimated. These biases involved, the incomplete data set and possible contaminating processes prevent us from obtaining information on the specific origin(s) of IDPs from elemental abundances.     

Noble gases in interplanetary dust particles,II: Excess helium‐3 in cluster particles and modeling constraints on interplanetary dust particle exposures to cosmic‐ray irradiation

Abstract— Measurements of He isotopes in cluster interplanetary dust particles (IDPs) from stratospheric dust collector L2009 reveal anomalous ³He/⁴He ratios comparable to those seen earlier, up to ～40x the solar wind ratio, in particles from the companion collector L2011. These overabundances of ³He in the L2009 samples are masked by much higher ⁴He contents compared to the L2011 particles, and are visible only in minor gas fractions evolved by stepwise heating at high temperatures. Cosmic‐ray induced spallogenic reactions are efficient producers of ³He. The majority of this paper is devoted to a detailed assessment of the possible role of spallation in generating the ³He excesses in these and other cluster IDPs. A model of collisional erosion and fragmentation during inward transit through the interplanetary dust environment is used to estimate space lifetimes of particles from asteroidal and Edgeworth–Kuiper Belt sources. Results of the modeling indicate that Poynting–Robertson orbital evolution timescales of IDPs small enough to elude destruction on their way to Earth from either location are far shorter than the cosmic‐ray exposure ages required to account for observed ³He overabundances. Grains large enough to have sufficiently long space residence times are fragmented close to their sources. An alternative to long in‐space exposure could be prolonged irradiation of particles buried in parent body regoliths prior to their ejection as IDPs. A qualitative calculation suggests, however, that collisional erosion of asteroidal upper‐regolith materials is likely to occur on timescales shorter than the > 1 Ga burial times needed for accumulation of spallogenic ³He to the levels seen in several cluster particles. In contrast, regoliths on Edgeworth–Kuiper Belt objects may be stable enough to account for the ³He excesses, and delivery of heavily pre‐irradiated IDPs to the inner solar system by short‐period Edgeworth–Kuiper Belt comets remains a possibility. A potential problem is that the expected associated abundances of spallation‐produced ²¹Ne appear to be absent, although here the present IDP data base is too sparse and for the most part too imprecise to rule out a spallogenic origin. Relatively short periods of pre‐ejection residence in asteroidal regoliths may be responsible for the curiously broad exposure age distributions reported for micrometeorites extracted from Greenland and sea‐floor sediments.     

Factors affecting the motion of interplanetary dust particles

In this paper the dynamics of individual dust particles and the effects on their motion caused by insolation and consequent evaporation is considered. Evaporation rates and the radii of dust-free zones have been computed using thermodynamic data from various sources. Some doubt is thrown on the validity of the process of matching observed thermal emission peaks with theoretical evaporation zone radii.     

Salts in two chondritic porous interplanetary dust particles

Abstract— Grain-by-grain analytical electron microscope analyses of two micrometeorites, or interplanetary dust particles (IDPs), of the chondritic porous subtype, show the presence of rare barite (BaSO₄) and magnesium carbonate, probably magnesite. Salt minerals in chondritic porous (CP) IDPs give evidence for in situ aqueous alteration in their parent bodies. The uniquely high barium content of CP IDP W7029^*C1 is consistent with barite precipitation from a mildly acidic (pH > ～5) aqueous fluid at temperatures below 417 K and low oxygen fugacity. The presence of magnesite in olivine-rich, anhydrous CP IDP W7010^*A2 is evidence that carbonate minerals occur in both the chondritic porous and chondritic smooth subtypes of chondritic IDPs. Citing Schramm et al. (1989) for putative asteroidal-type aqueous alteration in IDPs and probable sources of chondritic IDPs, salt minerals in CP IDPs could support low-temperature aqueous activity in nuclei of active short-period comets.     

Observation of saturnian stream particles in the interplanetary space

In January 2004 the dust instrument on the Cassini spacecraft detected the first high-velocity grain expelled from Saturn - a so-called stream particle. Prior to Cassini’s arrival at Saturn in July 2004 the instrument registered 801 faint impacts, whose impact signals showed the characteristic features of a high-velocity impact by a tiny grain. The impact rates as well as the directionality of the stream particles clearly correlate with the sector structure of the interplanetary magnetic field (IMF). The Cosmic Dust Analyser (CDA) registered stream particles dominantly during periods when the IMF direction was tangential to the solar wind flow and in the prograde direction. This finding provides clear evidence for a continuous outflow of tiny dust grains with similar properties from the saturnian system. Within the compressed part of co-rotating interaction regions (CIRs) of the IMF, characterized by enhanced magnetic field strength and compressed solar wind plasma, CDA observed impact bursts of faster stream particles. We find that the bursts result from the stream particles being sped up inside the compressed CIR regions. Our analysis of the stream-particle dynamics inside rarefaction regions of the IMF implies that saturnian stream particles have sizes between 2 and 9 nm and exit the saturnian systems closely aligned with the planet’s ring plane with speeds in excess of 70 km s⁻¹.     

Magnetic field modulated dust streams from Jupiter in interplanetary space

High speed dust streams emanating from near Jupiter were first discovered by the Ulysses spacecraft in 1992. Since then the phenomenon has been re-observed by Galileo in 1995, Cassini in 2000, and Ulysses in 2004. The dust grains are expected to be charged to a potential of , which is sufficient to allow the planet's magnetic field to accelerate them away from the planet, where they are subsequently influenced by the interplanetary magnetic field (IMF). A similar phenomenon was observed near Saturn by Cassini. Here, we report and analyze simultaneous dust, IMF and solar wind data for all dust streams from the two Ulysses Jupiter flybys. We find that compression regions (CRs) in the IMF – regions of enhanced magnetic field – precede most dust streams. Furthermore, the duration of a dust stream is roughly comparable with that of the precedent CR, and the occurrence of a dust stream and the occurrence of the previous CR are separated by a time interval that depends on the distance to Jupiter. The intensity of the dust streams and their precedent CRs are also correlated, but this correlation is only evident at distances from the planet no greater than 2 AU. Combining these observations, we argue that CRs strongly affect dust streams, probably by deflecting dust grain trajectories, so that they can reach the spacecraft and be detected by its dust sensor.     

Compositional variations of olivines and pyroxenes in chondritic interplanetary dust particles

Abstract We report here analyses of olivines and pyroxenes, and petrofabrics of 27 chondritic interplanetary dust particles (IDPs), comparing those from anhydrous and hydrous types. Approximately 40% of the hydrous particles contain diopside, a probable indicator of parent body thermal metamorphism, while this mineral is rarely present in the anhydrous particles. Based on this evidence, we find that hydrous and anhydrous IDPs are, in general, not directly related, and we conclude that olivine and pyroxene major-element compositions can be used to help discriminate between IDPs that are (1) predominantly nebular condensates, and lately resided in anhydrous or icy (no liquids) primitive parent bodies, and (2) those originating from more geochemically active parent bodies (probably hydrous and anhydrous asteroids).     

The porosity and permeability of chondritic meteorites and interplanetary dust particles

Abstract— We have investigated the porosity of a large number of chondritic interplanetary dust particles (IDPs) and meteorites by three techniques: standard liquid/gas flow techniques, a new, noninvasive ultrasonic technique, and image processing of backscattered images. The latter technique is obviously best-suited to sub-kilogram sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, nondestructive pressure release technique. We find that chondritic IDPs have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. Type 1–3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1–3 chondrites have the same approximate range as exhibited by the matrix, which indicates that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as the matrix. These results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar, which implies that similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, chondrite type or porosity.     

Diverse forms of primordial organic matter identified in interplanetary dust particles

Abstract– Coordinated in situ transmission electron microscopy and isotopic measurements of carbonaceous phases in interplanetary dust particles were performed to determine their origins. Five different types of carbonaceous materials were identified based on their morphology and texture, observed by transmission electron microscopy: globular, vesicular, dirty, spongy, and smooth. Flash heating experiments were performed to explore whether some of these morphologies are the result of atmospheric entry processes. Each of these morphologies was found to have isotopically anomalous H and N. Rare C isotopic anomalies were also observed. The isotopic and morphological properties of several of these phases, particularly the organic globules, are remarkably similar to those observed in other extraterrestrial materials including carbonaceous chondrites, comet 81P/Wild 2 particles collected by the Stardust spacecraft, and Antarctic micrometeorites, indicating that they were widespread in the early solar system. The ubiquitous nature and the isotopic anomalies of the nanoglobules and some other morphologies strongly suggest that these are very primitive phases. Given that some of the isotopic anomalies (D and ¹⁵N excesses) are indicative of mass fractionation chemical reactions in a very cold environment, and some others (¹³C and ¹⁵N depletions) have other origins, these carbonaceous phases come from different reservoirs. Whatever their origins, these materials probably reflect the first stages of the evolution of solar system organic matter, having originated in the outermost regions of the protosolar disk and/or interstellar cold molecular clouds.     

The thermal history of interplanetary dust particles collected in the Earth's stratosphere

Abstract— Fragments of 24 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were obtained from NASA's Johnson Space Center collection and subjected to pulse-heating sequences to extract He and Ne and to learn about the thermal history of the particles. A motivation for the investigation was to see if the procedure would help distinguish between IDPs of asteroidal and cometary origin. The use of a sequence of short-duration heat pulses to perform the extractions is an improvement over the employment of a step-heating sequence, as was used in a previous investigation. The particles studied were fragments of larger parent IDPs, other fragments of which, in coordinated experiments, are undergoing studies of elemental and mineralogical composition in other laboratories. While the present investigation will provide useful temperature history data for the particles, the relatively large size of the parent IDPs (～40 μm in diameter) resulted in high entry deceleration temperatures. This limited the usefulness of the study for distinguishing between particles of asteroidal and cometary origin.     

Ion bombardment of interplanetary dust

The recent discovery of ion tracks in interplanetary dust and the increasing evidence for carbon and carburized materials in these objects are strongly suggestive that chemical processing by energetic charged-particle bombardment has occured during the dust lifetimes. The track density gives a measure of the total ion fluence experienced by the grains. We use this information and laboratory data on the modification of icy surfaces by incident ions and electrons to discuss the likelihood that chondritic interplanetary dust particles could have been proceed, by plasma bombardment, from aggregates of particles which had volatile and/or ogranic mantles. Such a processing would leave carbon and carburized deposits and can affect estimates of the temperature of formation of these dust grains.     

Lorentz scattering of interplanetary dust

Charged dust grains in a turbulent magnetic field will see a Lorentz force due to the convection of the solar magnetic field past them at the solar wind velocity. Since the sign of this magnetic field is randomly varying, the direction of the force will be random, and the net effect will be to randomly scatter the orbital elements of these particles. The square roots of the mean square change in semimajor axis, inclination, and eccentricity are determined as a function of the particles' original orbital elements. Particles 3 μm in radius and smaller will have their motions strongly perturbed or dominated by Lorentz scattering. This scattering will have an effect comparable to, or greater than, the Poynting-Robertson effect on these particles for time scales comparable to their Poynting-Robertson lifetimes.     

Cosmogenic production rates and recoil loss effects in micrometeorites and interplanetary dust particles

We present a purely physical model to determine cosmogenic production rates for noble gases and radionuclides in micrometeorites (MMs) and interplanetary dust particles (IDPs) by solar cosmic‐rays (SCR) and galactic cosmic‐rays (GCR) fully considering recoil loss effects. Our model is based on various nuclear model codes to calculate recoil cross sections, recoil ranges, and finally the percentages of the cosmogenic nuclides that are lost as a function of grain size, chemical composition of the grain, and the spectral distribution of the projectiles. The main advantage of our new model compared with earlier approaches is that we consider the entire SCR particle spectrum up to 240 MeV and not only single energy points. Recoil losses for GCR‐produced nuclides are assumed to be equal to recoil losses for SCR‐produced nuclides. Combining the model predictions with Poynting‐Robertson orbital lifetimes, we calculate cosmic‐ray exposure ages for recently studied MMs, cosmic spherules, and IDPs. The ages for MMs and the cosmic‐spherule are in the range <2.2–233 Ma, which corresponds, according to the Poynting‐Robertson drag, to orbital distances in the range 4.0–34 AU. For two IDPs, we determine exposure ages of longer than 900 Ma, which corresponds to orbital distances larger than 150 AU. The orbital distance in the range 4–6 AU for one MM and the cosmic spherule indicate an origin either in the asteroid belt or release from comets coming either from the Kuiper Belt or the Oort Cloud. Three of the studied MMs have orbital distances in the range 23–34 AU, clearly indicating a cometary origin, either from short‐period comets from the Kuiper Belt or from the Oort Cloud. The two IDPs have orbital distances of more than 150 AU, indicating an origin from Oort Cloud comets.     

Formation of carbides and hydrocarbons in chondritic interplanetary dust particles: A laboratory study

Abstract— The reaction between kamacite grains and H₂ + CO gas mixture has been tested in the laboratory under experimental conditions presumed for interplanetary dust particle (IDP) formation in a nebular-type environment (H₂:CO = 250:1; 5 × 10^?4 atm total pressure, and 473 K). Carbon deposition, hydrocarbon production in the C₁–C₄ range, and the formation of an ?-carbide phase occur when well-defined model FeNi bcc alloy (kamacite) particles are exposed to a mixture of H₂ + CO during 10³ h. These results strongly support the idea that gas-solid reactions in the solar nebula during CO hydrogenation represent a plausible scenario for the formation of carbides and carbonaceous materials in IDPs, as well as for the production of hydrocarbons through Fischer-Tropsch-type reactions.