Cometary Interplanetary Dust Particles Research Articles

Correlated IR-SEM-TEM studies of three different grains from Ryugu: From the initial material to post-accretional processes

In order to better constrain the alteration history of the Ryugu parent body, we performed a multi-analytical study combining scanning electron microscopy, transmission electron microscopy and infrared spectroscopy on sections extracted from the three fragments A0064-FO019, A0064-FO021 and C0002-FO019 returned from Ryugu by the Hayabusa2 space mission. The three sections show large differences in terms of structure, mineralogy and infrared signature. Section A0064-FO019 resembles the major Ryugu lithology with the presence of both fine-grained phyllosilicates (fg-phyllos) with embedded nanosulfides and coarse-grained phyllosilicates (cg-phyllos), whereas section C0002-FO019 belongs to the group of the less altered lithologies with the presence of anhydrous minerals embedded in a partially amorphous matrix. Section A0064-FO021 also belongs to this group but shows two different lithologies, a compact amorphous one and a more porous and very fractured one showing the presence of Na-rich phosphate, calcite and olivine. The two less altered lithologies (sections A0064-FO021 and C0002-FO019) show the presence of numerous mineralogical features similar to those observed in cometary interplanetary dust particles, ultra-carbonaceous Antarctic micrometeorites or in the CM Paris meteorite, i.e. amorphous and partially crystallized matrix with GEMS-like ghosts objects, whisker olivine, phosphide, or FeNi metal. This supports an outer solar system origin common with that of cometary material for the Ryugu parent body. Combined with the results of Nakamura et al. (2022b) reporting the presence of a lithology showing the presence of GEMS-like objects, we propose that section C0002-FO019 represents the onset of aqueous alteration of such primitive materials. The cg-phyllos and fg-phyllos of section A0064-FO019, i.e. of the major Ryugu lithology, representing the advanced stage of alteration, exhibit distinctive IR signatures with a higher abundance of oxygen-rich functional groups in the organic matter (OM) from the cg-phyllos. We thus suggest the following chronology of formation and evolution for Ryugu: (1) accretion of highly porous aggregate of GEMS-like units with fine-grained high-temperature anhydrous silicates, (2) onset of alteration with the dissolution of primary nanosulfides and development of amorphous/partially crystallized material in the pores, (3) crystallization of fg-phyllos with a second generation of sulfides, (4) later formation of cg-phyllos devoid of nanosulfides and their associated oxygen-rich OM in a more water-rich environment.

Northwest Africa 11024—A heated and dehydrated unique carbonaceous (CM) chondrite

AbstractBased on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.

Multiple generations of grain aggregation in different environments preceded solar system body formation

The solar system formed from interstellar dust and gas in a molecular cloud. Astronomical observations show that typical interstellar dust consists of amorphous (a-) silicate and organic carbon. Bona fide physical samples for laboratory studies would yield unprecedented insight about solar system formation, but they were largely destroyed. The most likely repositories of surviving presolar dust are the least altered extraterrestrial materials, interplanetary dust particles (IDPs) with probable cometary origins. Cometary IDPs contain abundant submicron a-silicate grains called GEMS (glass with embedded metal and sulfides), believed to be carbon-free. Some have detectable isotopically anomalous a-silicate components from other stars, proving they are preserved dust inherited from the interstellar medium. However, it is debated whether the majority of GEMS predate the solar system or formed in the solar nebula by condensation of high-temperature (>1,300 K) gas. Here, we map IDP compositions with single nanometer-scale resolution and find that GEMS contain organic carbon. Mapping reveals two generations of grain aggregation, the key process in growth from dust grains to planetesimals, mediated by carbon. GEMS grains, some with a-silicate subgrains mantled by organic carbon, comprise the earliest generation of aggregates. These aggregates (and other grains) are encapsulated in lower-density organic carbon matrix, indicating a second generation of aggregation. Since this organic carbon thermally decomposes above ∼450 K, GEMS cannot have accreted in the hot solar nebula, and formed, instead, in the cold presolar molecular cloud and/or outer protoplanetary disk. We suggest that GEMS are consistent with surviving interstellar dust, condensed in situ, and cycled through multiple molecular clouds.

Trapping and dynamical evolution of interplanetary dust particles in Earth’s quasi-satellite resonance

We used numerical simulations to model the orbital evolution of interplanetary dust particles (IDPs) evolving inward past Earth’s orbit under the influence of radiation pressure, Poynting–Robertson light drag (PR drag), solar wind drag, and gravitational perturbations from the planets. A series of β values (where β is the ratio of the force from radiation pressure to that of central gravity) were used ranging from 0.0025 up to 0.02. Assuming a composition consistent with astronomical silicate and a particle density of 2.5gcm−3 these β values correspond to dust particle diameters ranging from 200μm down to 25μm. As the dust particle orbits decay past 1AU between 4% (for β=0.02, or 25μm) and 40% (for β=0.0025, or 200μm) of the population became trapped in 1:1 co-orbital resonance with Earth. In addition to traditional horseshoe type co-orbitals, we found about a quarter of the co-orbital IDPs became trapped as so-called quasi-satellites. Quasi-satellite IDPs always remain relatively near to Earth (within 0.1–0.3AU, or 10–30Hill radii, RH) and undergo two close-encounters with Earth each year. While resonant perturbations from Earth halt the decay in semi-major axis of quasi-satellite IDPs their orbital eccentricities continue to decrease under the influence of PR drag and solar wind drag, forcing the IDPs onto more Earth-like orbits. This has dramatic consequences for the relative velocity and distance of closest approach between Earth and the quasi-satellite IDPs. After 104–105years in the quasi-satellite resonance dust particles are typically less than 10RH from Earth and consistently coming within about 3RH. In the late stages of evolution, as the dust particles are escaping the 1:1 resonance, quasi-satellite IDPs can have deep close-encounters with Earth significantly below RH. Removing the effects of Earth’s gravitational acceleration reveals that encounter velocities (i.e., velocities “at infinity”) between quasi-satellite IDPs and Earth during these close-encounters are just a few hundred meters per second or slower, well below the average values of 2–4kms−1 for non-resonant Earth-crossing IDPs with similar initial orbits. These low encounter velocities lead to a factor of 10–100 increase in Earth’s gravitationally enhanced impact cross-section (σgrav) for quasi-satellite IDPs compared to similar non-resonant IDPs. The enhancement in σgrav between quasi-satellite IDPs and cometary Earth-crossing IDPs is even more pronounced, favoring accretion of quasi-satellite dust particles by a factor of 100–3000 over the cometary IDPs. This suggests that quasi-satellite dust particles may dominate the flux of large (25–200μm) IDPs entering Earth’s atmosphere. Furthermore, because quasi-satellite trapping is known to be directly correlated with the host planet’s orbital eccentricity the accretion of quasi-satellite dust likely ebbs and flows on 105year time scales synchronized with Earth’s orbital evolution.

Insight into the silicate and organic reservoirs of the comet forming region

Cometary interplanetary dust particles (IDPs), collected in Earth’s stratosphere, currently represent the best way to sample outer Solar System primordial dust. The fine-grained (sub-μm) minerals of IDPs show some strong similarities to the textures expected for primary condensates from the solar nebula. In this study we have analysed a set of IDPs for combined bulk carbon, nitrogen and hydrogen isotopes, and high precision oxygen isotopes by NanoSIMS 50L. This study concentrates on combining isotopic analyses, including high precision oxygen, on the silicate and organic components within the same sample on fine-grained primordial materials. Oxygen isotope analyses reveal that some IDPs are more 16O-rich than any bulk meteorite compositions, extending to O isotope compositions in between chondritic- and solar-like values (δ17O=−20‰, δ18O=−20‰). The 16O-rich IDPs display more primitive organic signatures than the chondritic-like 16O-poor IDPs but, rather interestingly, they also have lower presolar grain abundances. The 16O-poor signatures probably indicate an abundant component of chondritic-like material, processed in the inner protoplanetary disk. In order to explain the association of relatively processed material (silicates and organics) with high presolar grain abundances we propose a model whereby the initial dust component is 16O-rich (solar-like) and originally present homogenously throughout the protoplanetary disk. Outward radial transport, potentially associated with aerodynamic sorting, led to an influx of processed silicates from the inner Solar System with chondritic-like isotopic signatures. Comet accretion that occurred late, or at smaller heliocentric distance, included higher abundances of this chondritic-like component and hence had more 16O-poor O isotope compositions. Presolar grains, whose extreme isotopic signatures were destroyed during early homogenisation of solar nebula dust, continue to accrete onto the protoplanetary disk with time such that the later-formed comets, those with a higher proportion of processed silicates within their source, also had time to accumulate a higher abundance of presolar grains. A similar pattern is observed in the organics, with decreasing δD and C/H, from increased exchange with nebula gas, in IDPs that contain more 16O-poor chondritic-like material.

Raman Spectroscopy on Cometary and Meteoritic Organic Matter

ABSTRACT Extraterrestrial organic matter (OM) is an important component of meteorites that originate from asteroids and from cometary dust collected from comet Wild 2 and the Earth's atmosphere. Some of this OM was incorporated into the first planetary bodies during the formation of the solar system, 4.56 Ga ago, and did not experience significant alteration. Here, we summarize our efforts in the comparative C Raman spectroscopy of this OM. We aim for the identification of the most primitive OM that might be of solar nebula origin and a better understanding of the modifying processes on parent bodies, during transport in space and sample collection. We (i) determine the degree of order of meteoritic OM and hence the metamorphism experienced on their parent bodies; (ii) assess potential effects during sample collection of comet Wild 2 dust, and (iii) compare possibly cometary interplanetary dust particles (IDPs) with primitive meteorites.

Investigation of iron sulfide impact crater residues: A combined analysis by scanning and transmission electron microscopy

Abstract– Samples returned from comet 81P/Wild 2 by the Stardust mission provided an unequaled opportunity to compare previously available extraterrestrial samples against those from a known comet. Iron sulfides are a major constituent of cometary grains commonly identified within cometary interplanetary dust particles (IDPs) and Wild 2 samples. Chemical analyses indicate Wild 2 sulfides are fundamentally different from those in IDPs. However, as Wild 2 dust was collected via impact into capture media at approximately 6.1 km s−1, it is unclear whether this is due to variation in preaccretional/parent body processes experienced by these materials or due to heating and alteration during collection. We investigated alteration in pyrrhotite and pentlandite impacted into Stardust flight spare Al foils under encounter conditions by comparing scanning and transmission electron microscope (SEM, TEM) analyses of preimpact and postimpact samples and calculating estimates of various impact parameters. SEM is the primary method of analysis during initial in situ examination of Stardust foils, and therefore, we also sought to evaluate the data obtained by SEM using insights provided by TEM. We find iron sulfides experience heating, melting, separation, and loss of S, and mixing with molten Al. These results are consistent with estimated peak pressures and temperatures experienced (approximately 85 GPa, approximately 2600 K) and relative melting temperatures. Unambiguous identification of preserved iron sulfides may be possible by TEM through the location of Al‐free regions. In most cases, the Ni:Fe ratio is preserved in both SEM and TEM analyses and may therefore also be used to predict original chemistry and estimate mineralogy.

The Question of Presolar Components within Interplanetary Dust Particles (IDPs) Collected in the Stratosphere

AbstractInterplanetary dust particles (IDPs) are from asteroids and comets, and they are the smallest and most fine-grained meteoritic objects available for laboratory investigation. Cometary IDPs are of special significance because they are presently the only samples of comets, and comets are expected to be enriched in preserved solar nebula and presolar components. These components may include not only cosmically rare refractory circumstellar grains(e.g. SiC) that are recovered from meteorites but also cosmically abundant interstellar silicates and carbonaceous grains that were the fundamental building blocks of the Solar System. D/H ratios measured in IDPs are consistent with the survival of interstellar carbonaceous material, and some IDPs contain glassy grains with properties similar to those of interstellar “amorphous silicates”. Submicrometer forsterite and enstatite crystals in IDPs resemble circumstellar silicates detected by the Infrared Space Observatory (ISO). ISO also detected a broad ~ 23 µm feature around several stars, and a similar feature observed in IDP spectra is due to submicrometer FeNi sulfide grains, suggesting that sulfide grains may be a significant constituent of astronomical dust.

A 35 Myr record of helium in pelagic limestones from Italy: implications for interplanetary dust accretion from the early Maastrichtian to the middle Eocene

We have determined the helium concentration and isotopic composition of a suite of early Maastrichtian through middle Eocene pelagic limestones in the Italian Apennines. The results provide a 35 Myr record of the implied flux of extraterrestrial 3He, which is a proxy for the accretion rate of interplanetary dust particles (IDPs). Our measurements show that the 3He flux was fairly constant in the Maastrichtian, except for possible minor increases (factor of two or less) from ∼70.5 Ma to 68 Ma and at ∼66 Ma, which probably reflect transient increases in the accretion rate of asteroidal and/or cometary IDPs. We find no evidence for an increase in IDP accretion at or immediately before the K/T boundary, implying that the K/T impact was not associated with enhanced solar system dustiness. This observation precludes the possibility that the K/T impactor was a member of a major comet shower, and is more consistent with impact of a lone comet or asteroid. Our data suggest a 2 to 4 fold increase in IDP accretion between 57 and 54 Ma, followed by a factor of three decrease over an ∼4 Myr period in the early to middle Eocene. The duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets, and is more likely the result of collisions in the asteroid belt/and or Kuiper belt. In the entire 35 Myr record we find no evidence for major enhancements of the IDP accretion rate of the type expected from comet showers. Our results, in combination with earlier 3He measurements, do not support models that predict recurrent comet showers with periods of <38 Myrs. If there is a periodicity in the cratering record that is caused by periodic modulation of the Oort cloud, it is not evident in the Apennine sediment data. Along with the 3He measurements we also obtained 4He concentrations, which record temporal changes in the flux or composition of terrigenous matter. The most significant change in 4He occurs in the last 4 Myrs of the Cretaceous, over which the concentration of 4He in the detrital component rises by 300%. This rise tracks a strong increase in the seawater 87Sr/ 86Sr ratio, suggesting a globally significant change in the composition of continental detritus delivered to the oceans, possibly arising from increased continental weathering.

Transmission Electron Microscopy Studies of Natural Nanomaterials from the Solar System

It is widely appreciated that the study of (man-made) nanomaterials is a new frontier in materials science, but it is not well appreciated that (natural) nanomaterials represent a new frontier in meteoritics and planetary science [1]. During the next decade the nanogram to microgram quantities of extraterrestrial materials will be returned to Earth from a variety of solar system bodies including comets [2]. Studies of cometary interplanetary dust particles (IDPs) collected in the stratosphere, as well as mass spectrometry data from grains analyzed in-situ at comet Halley, suggest that the returned comet samples will be heterogeneous on a scale of nanometers [3, 4]. (A single 5-10μm diameter IDP may contain &gt;106 individual grains and many different minerals (metal, carbonaceous phases, silicates, sulfides, etc.)). More recent observations of dust around stars, in interplanetary space, and at comet Hale-Bopp indicate that the predominant astronomical grain size is in the nanometer to submicrometer size range [5,6].

Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale‐Bopp) Pre‐ and Postperihelion

We present 7.5-13.4 μm infrared (IR) spectrophotometry (R≃180-360) of the 10 μm silicate emission from dust in the inner coma (i.e., within a diameter of 3'') of comet C/1995 O1 (Hale-Bopp) at four temporal epochs from 1996 October through 1997 June during Hale-Bopp's approach to, arrival at, and recession from perihelion. Hale-Bopp's silicate feature is the strongest observed from any comet to date: the flux-to-continuum ratio at 10.0 μm is 2.5 at 2.8 AU preperihelion, increases to 3.0 at 0.93 AU, and then decreases to 2.4 at 1.7 AU postperihelion, dropping more rapidly in strength than expected from preperihelion spectra and indicating a diminishment in the relative abundance of submicron sized grains by perihelion passage. The silicate feature also evolves with heliocentric distance. When far from perihelion, at ~2.8 AU, the High Efficiency Faint Object Grating Spectrometer (HIFOGS) 10 μm silicate feature contains a 9.3 μm shoulder attributable to amorphous pyroxene, broad emission from amorphous olivine (9.7 μm), and the 11.2 μm peak associated with crystalline olivine. Concurrent with the HIFOGS spectra at 2.8 AU, the Infrared Space Observatory (ISO) Short Wavelength Spectrometer (SWS) spectrum also shows the strong far-IR peaks of crystalline olivine at 18 μm, 23 μm, and 33 μm. When close to perihelion the HIFOGS spectra include a newly discovered 9.3 μm peak, identifiable as Mg-rich crystalline pyroxene. We hypothesize that the crystalline pyroxenes are cooler than the other silicates, too cool to be detected at 9.3 μm at 2.8 AU but warm enough to be detected at 1.2 AU. The best-fit empirical model for the temporal evolution of Hale-Bopp's silicate feature constrains the Mg-rich crystalline pyroxenes to be dominated by ortho-pyroxene rather than clino-pyroxene. The crystalline pyroxenes have a color temperature that is 0.6 times cooler than and an abundance that is about 9 times greater than the other silicates at all epochs, assuming equivalent particle size distributions for all components. Comparing crystalline ortho-pyroxene and crystalline olivine in radiative equilibrium, both with Mg number 0.9, the ortho-pyroxene crystals are cooler because they are less absorbing at visible and near-IR wavelengths. Thus, it is the high Mg content of the crystalline pyroxenes that accounts for their cooler temperature. The dominance of Mg-rich pyroxenes among Hale-Bopp's cometary silicates is consistent with PUMA-1 mass spectrometer measurements of comet P/Halley 1986 III and with cometary interplanetary dust particles. The high Mg content of the pyroxenes in comet Hale-Bopp implies that they are either pristine solar nebula condensates or presolar grains such as the Mg-rich crystals recently discovered by ISO around asymptotic giant branch stars.