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Evaluation of mineralogical alteration of mcrometeoroid analog materials captured in aerogel
Abstract
Silica aerogel has been used as a capturing medium for micrometeoroids and space debris. Several previous investigations suggest that aerogel could capture hypervelocity particles macroscopically intact. However, it has not been fully evaluated whether retrieved grains retain their pristine mineralogy. This study attempts to evaluate the intact survivability of high-speed projectiles in aerogel using impact experiments. Such experiments are essential for rigorous examination or further scientific discussion on the samples of on-going and future sample return missions in which aerogels are/will be used as capturing media. We fired two kinds of micrometeoroid analog materials into aerogel with a two-stage light gas gun (2–4 km/s), serpentine and cronstedtite, which are commonly found in CM/CI, and CM chondrites, respectively. As these hydrated minerals are broken down into anhydrous ones at relatively low temperatures, it is suitable for the evaluation of thermal alteration during the capturing process. The retrieved residues were examined with SEM/EDS, Synchrotron Radiation-XRD, and TEM/EDS. The SR-XRD analysis revealed that most of the volumes of residues are mineralogically unaltered. TEM observations show that one serpentine grain shot at 4 km/s has an unaltered crystalline part inside, an amorphous layer, and the outermost molten aerogel layer. One cronstedtite grain shot at 3 km/s, also examined by TEM, was found to have an unaltered interior as well as a vesiculated silicate melt layer. Image analysis revealed both mineral grains reduced their volume down to 10% of the original on average. These results suggest that it is possible to capture serpentine and cronstedtite particles mineralogically intact with the aerogel, at least in the interior of each particle, below 4 km/s, in spite of their large volume loss.
... Low-density silica aerogels have been used to capture small particles traveling at high velocities in several space missions, such as the cometary dust particles from the Comet 81P/Wild 2 on the Stardust mission . An ultralow-density silica aerogel (0.01 g/ cm 3 ) has been developed at Chiba University for the Tanpopo mission which has an astrobiology space experiment at the Japanese Experiment Mod-intact after 2-6 km/s impact into 0.03 g/cm 3 density aerogel, despite the significant volume loss from the particle's outside surface during the penetration processes (Noguchi et al., 2007;Okudaira et al., 2004). For example, detailed examination of the "keystone" samples from the Stardust mission, showed that the upper parts of the entrant hollow tracks are lined with relatively large amounts of melted aerogel and dissolved projectile, but the track ends contain largely un-melted cometary fragments . ...
... The Murchison powder samples (micron-sized grains) were placed in sabots and fired into silica aerogels (0.01 g/cm 3 ) by a two-stage light-gas gun at ISAS, JAXA. Experimental conditions are summarized in Table 1 with details of the experimental methods described in Okudaira et al. (2004). We used the flight-grade ultralow-density (0.01 g/cm 3 ) aerogel developed to capture cosmic dust particles. ...
... Previous experiments using serpentine and cronstedtite reported that the maximum surface temperature reached 2000 ± 200 K (2273 ± 200∞C) but noted that several-micrometers into the interior of the sample, grains were left intact after 2-4 km/s impact into 0.03 g/cm 3 aerogel (Okudaira et al., 2004). Additional higher velocity (>6 km/s) impact experiments indicate that the impact of the grains (<2 mm thick) had steep thermal gradients 2500∞C/mm from the surface to the interior, with the center below 300∞C (Noguchi et al., 2007). ...
The Tanpopo mission is an astrobiology space experiment at the Japanese Experiment Module (JEM) 'Kibo' on the International Space Station (ISS). One of the sub-divided themes of the Tanpopo mission is for the intact capture of organic bearing micrometeoroids in low Earth orbit using ultralow density silica aerogel (0.01 g/cm3). In order to evaluate damage to organic matter in micrometeoroids during hyper velocity impacts into the aerogel, Murchison meteorite powdered samples, analogs of organic bearing micrometeoroids, were fired into flight-grade silica aerogel (0.01 g/cm3) using a two-stage light-gas gun with velocities of 4.4 and 5.9 km/s. The recovered Murchison grains were analyzed using scanning transmission X-ray microscopy/X-ray absorption near edge structure (STXM/XANES), transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS). TEM observation did not show significant modifications of the recovered Murchison grains. Carbon-XANES spectra, however, showed a large depletion of the organic matter after the 5.9 km/s impact, but no such effects nor any significant hydrogen isotopic fractionation were observed after the 4.4 km/s impact.
... Dense aerogel (60 kg m )3 and above) came from Matsushita Electronics Works, Japan. Lower density aerogel blocks came from Chiba in Japan (see Okudaira et al. 2004) or were manufactured in house at Kent (Foster 2006;Burchell et al. 2009a). Peter Tsou and Steve Jones of the Jet Propulsion Laboratory supplied two types of graded aerogel similar to that flown on Stardust: from Peter Tsou came ''flight spare'' Stardust aerogel (FSSA, manufactured as described in Tsou et al. 2003;and as used in Burchell et al. 2008a); the new aerogel samples used in later shots were manufactured by the same method, and are referred to as ''flight-quality'' Stardust aerogel (FQSA, see Jones [2007] for details of their manufacture). ...
... In addition, two hydrous silicates (lizardite Mgserpentine, and the Fe-silicate cronstedtite) were shot, as similar materials might have been expected in Stardust samples had there been substantial aqueous parent body processing on the comet Wild 2 nucleus. Alteration of these two minerals during hypervelocity capture in aerogel has also been described by Okudaira et al. (2004Okudaira et al. ( , 2005 and Noguchi et al. (2007), but the preimpact morphology of their projectiles was not described, and little information was given as to track shape. ...
... Published transmission electron microscope (TEM) images of captured hydrous silicate particles (approximately 15% H 2 O by weight in lizardite and approximately 9% in cronstedtite) have shown that much of the particle mass is lost during creation of their tracks, with amorphization, melting, and vesiculation within the surface of the remaining particle (Okudaira et al. 2004(Okudaira et al. , 2005, although the center still may retain original structure (Noguchi et al. 2007). This implies that both lizardite and cronstedtite must lose abundant water as vapor, yet the tracks created by these impacts of cronstedtite and lizardite were not described as bulbous in shape, even though Yano et al. (1999) have shown that lower velocity ice impacts do yield shallow bulbous tracks. ...
The Stardust collector shows diverse aerogel track shapes created by
impacts of cometary dust. Tracks have been classified into three broad
types (A, B, and C), based on relative dimensions of the elongate
"stylus" (in Type A "carrots") and broad "bulb" regions (Types B and C),
with occurrence of smaller "styli" in Type B. From our experiments,
using a diverse suite of projectile particles shot under Stardust
cometary encounter conditions onto similar aerogel targets, we describe
differences in impactor behavior and aerogel response resulting in the
observed range of Stardust track shapes. We compare tracks made by
mineral grains, natural and artificial aggregates of differing subgrain
sizes, and diverse organic materials. Impacts of glasses and robust
mineral grains generate elongate, narrow Type A tracks (as expected),
but with differing levels of abrasion and lateral branch creation.
Aggregate particles, both natural and artificial, of a wide range of
compositions and volatile contents produce diverse Type B or C shapes.
Creation of bulbous tracks is dependent upon impactor internal
structure, grain size distribution, and strength, rather than overall
grain density or content of volatile components. Nevertheless, pure
organic particles do create Type C, or squat Type A* tracks, with length
to width ratios dependent upon both specific organic composition and
impactor grain size. From comparison with the published shape data for
Stardust aerogel tracks, we conclude that the abundant larger Type B
tracks on the Stardust collector represent impacts by particles similar
to our carbonaceous chondrite meteorite powders.
... Accordingly, we have been using fine-grained minerals that have low decomposition temperatures and finegrained fragments of Murchison CM chondrite. We used this meteorite not because its mineralogy is thought to be similar to the mineralogy of cometary dust, but because it contains minerals with low decomposition temperatures (Okudaira et al. 2002(Okudaira et al. , 2003(Okudaira et al. , 2004. In these earlier studies, we found that antigorite and cronstedtite were melted, vesiculated, and mixed with surrounding aerogel during capture only on their surfaces, although cronstedtite experienced more severe melting than antigorite when both were shot at 3-4 km s 1 . ...
... They were shot at normal incidence to the surface of aerogel. Details of the experimental conditions of the two-stage lightgas guns have been described in Okudaira et al. (2003Okudaira et al. ( , 2004. The density of silica aerogel used in this study is 0.03 g/cm 3 . ...
... Although the reduction of grain size during capture in aerogel has been already discussed by Okudaira et al. (2004), in which samples were shot at <4.5 km/s, the reduction of size is more conspicuous in this study. Grain sizes of captured projectile grains are much smaller than those of original ones. ...
Abstract— Outside the Earth's atmosphere, silica aerogel is one of the best materials to capture finegrained extraterrestrial particles in impacts at hypervelocities. Because silica aerogel is a superior insulator, captured grains are inevitably influenced by frictional heat. Therefore, we performed laboratory simulations of hypervelocity capture by using light-gas guns to impact into aerogels finegrained powders of serpentine, cronstedtite, and Murchison CM2 meteorite. The samples were shot at >6 km s−1 similar to the flyby speed at comet P/Wild-2 in the Stardust mission. We investigated mineralogical changes of each captured particle by using synchrotron radiation X-ray diffraction (SR-XRD), transmission electron microscope (TEM), and field emission scanning electron microscope (FE-SEM). SR-XRD of each grain showed that the majority of the bulk grains keep their original mineralogy. In particular, SR-XRD and TEM investigations clearly exemplified the presence of tochilinite whose decomposition temperature is about 300 °C in the interior of the captured Murchison powder. However, TEM study of these grains also revealed that all the samples experienced melting and vesiculation on the surface. The cronstedtite and the Murchison meteorite powder show remarkable fracturing, disaggregation, melting, and vesiculation. Steep thermal gradients, about 2500 °C/μm were estimated near the surface of the grains (<2 μm thick) by TEM observation. Our data suggests that the interior of >4 μm across residual grains containing abundant materials that inhibit temperature rise would have not experienced >300 °C at the center.
... However, a capture experiment of microbes in space has never been attempted. The extremely large kinetic impact energies of projectiles accelerated to hypervelocities causes heat-induced physical transformations including decreases in the volumes and vitrification of the projectiles and target material (Okudaira et al. 2004;Noguchi et al. 2007). Airborne microbes have been transported on dust particles, e.g., clay minerals, through the atmosphere (Kellogg and Griffin 2006;Womack et al. 2010;Smith et al. 2013). ...
... Many small particles were observed near the track termini and on the tracks themselves (Fig. 6a), suggesting that the original particles had fragmented. We and others have shown that the interiors of other types of particle projectiles, e.g., serpentine, cronstedtite, and cocoa powder, do not experience temperatures higher than their decomposition temperatures (Okudaira et al. 2004;Noguchi et al. 2007;Spencer et al. 2009), suggesting that any DNA from microbes in the interior of the Tanpopo particles would not be subjected to temperatures that would affect its integrity. Therefore, it should be possible to capture particles of~60 m in diameter and to detect microbial DNA in the particles using the aerogel manufactured for the Tanpopo mission. ...
We have proposed an experiment (the Tanpopo mission) to capture microbes on the Japan Experimental Module of the International Space Station. An ultra low-density silica aerogel will be exposed to space for more than 1 year. After retrieving the aerogel, particle tracks and particles found in it will be visualized by fluorescence microscopy after staining it with a DNA-specific fluorescence dye. In preparation for this study, we simulated particle trapping in an aerogel so that methods could be developed to visualize the particles and their tracks. During the Tanpopo mission, particles that have an orbital velocity of ~8 km/s are expected to collide with the aerogel. To simulate these collisions, we shot Deinococcus radiodurans-containing Lucentite particles into the aerogel from a two-stage light-gas gun (acceleration 4.2 km/s). The shapes of the captured particles, and their tracks and entrance holes were recorded with a microscope/camera system for further analysis. The size distribution of the captured particles was smaller than the original distribution, suggesting that the particles had fragmented. We were able to distinguish between microbial DNA and inorganic compounds after staining the aerogel with the DNA-specific fluorescence dye SYBR green I as the fluorescence of the stained DNA and the autofluorescence of the inorganic particles decay at different rates. The developed methods are suitable to determine if microbes exist at the International Space Station altitude.
... In a study of alteration of hydrated mineral grains (serpentine and cronstedtite) during capture in aerogel (30 kg m −3 ) at 2-4 km s −1 , Okudaira et al. (2004) stated that the captured volumes were only 10% of the original grain volume. However, this was obtained by assuming that the grain size at impact was given by the entrance hole size in the aerogel and comparing this with the volume of the captured grains. ...
... In a later report (Okudaira et al. 2005), the same authors estimated that at 6 km s −1 , between 10% and 100% of the incident particle was captured intact in the aerogel. In both cases (Okudaira et al. 2004(Okudaira et al. , 2005 a mineralogical analysis of the captured grains was carried out. They found that there was no anhydrous decomposition of these hydrated minerals. ...
Aerogel is an ultra-low-density material that can be used to capture small particles incident upon it at speeds in excess of 1 km s−1. This permits capture of cosmic dust in space where the high speeds usually result in destructive impact events. The performance of aerogel in laboratory impact tests is described. Completely intact capture is rare; most studies show that between 10% to 100% of the incident particle's mass is captured. However, in all cases unaltered domains were found in the particles captured in the laboratory at speeds up to 6 or 7 km s−1. Several analytic techniques can be applied in situ to particles captured in aerogel, yielding data on the preimpact composition of the particle. Extraction techniques for removing small particles from aerogel are described, and after extraction, handling and analysis in the laboratory can proceed as for any small-sized particle. Coupled with the survival of intact regions in the captured particles, this allows detailed identification of the com...
... Prior to the Stardust mission, the performance of the aerogel capture medium was tested by hypervelocity impact experiments using light-gas guns (Barrett et al. 1992; Hörz et al. 1998; Burchell et al. 1999; Burchell et al. 2006a) and in analog studies of debris material captured in low Earth orbit (e.g., Hörz et al. 2000). A variety of minerals survived in these experiments without significant melting, including delicate, large (100 microns in size) grains of minerals such as phyllosilicates and carbonates (Okudaira et al. 2004; Noguchi et al. 2007; Burchell et al. 2006b). Varying degrees of volatilization, melting, and ablation were demonstrated (Barrett et al. 1992; Okudaira et al. 2004; Noguchi et al. 2007). ...
... A variety of minerals survived in these experiments without significant melting, including delicate, large (100 microns in size) grains of minerals such as phyllosilicates and carbonates (Okudaira et al. 2004; Noguchi et al. 2007; Burchell et al. 2006b). Varying degrees of volatilization, melting, and ablation were demonstrated (Barrett et al. 1992; Okudaira et al. 2004; Noguchi et al. 2007). The recovered materials were frequently shattered, melted, and encased within the melted aerogel in which they stopped. ...
We report the results of high-resolution, analytical and scanning transmission electron microscopy (STEM), including intensive element mapping, of severely thermally modified dust from comet 81P/Wild 2 caught in the silica aerogel capture cells of the Stardust mission. Thermal interactions during capture caused widespread melting of cometary silicates, Fe-Ni-S phases, and the aerogel. The characteristic assemblage of thermally modified material consists of a vesicular, silica-rich glass matrix with abundant Fe-Ni-S droplets, the latter of which exhibit a distinct core-mantle structure with a metallic Fe,Ni core and a iron-sulfide rim. Within the glassy matrix, the elemental distribution is highly heterogeneous. Localized amorphous "dust-rich" patches contain Mg, Al, and Ca in higher abundances and suggest incomplete mixing of silicate progenitors with molten aerogel. In some cases, the element distribution within these patches seems to depict the outlines of ghost mineral assemblages, allowing the reconstruction of the original mineralogy. A few crystalline silicates survived with alteration limited to the grain rims. The Fe- and CI-normalized bulk composition derived from several sections show CI-chondrite relative abundances for Mg, Al, S, Ca, Cr, Mn, Fe, and Ni. The data indicate a 5 to 15% admixture of fine-grained chondritic comet dust with the silica glass matrix. These strongly thermally modified samples could have originated from a finegrained primitive material, loosely bound Wild 2 dust aggregates, which were heated and melted more efficiently than the relatively coarse-grained material of the crystalline particles found elsewhere in many of the same Stardust aerogel tracks (Zolensky et al. 2006).
... The robust base layer with a bottom thickness of 7 mm helped mechanically support the fragile, lower-density surface layer over the orbital operation period, including rocket launch. The two aerogel densities were clearly distinguished at the boundary, which facilitates ground-based hypervelocity impact simulation studies (e.g., Okudaira et al., 2004;Ogata et al., 2013;Kawaguchi et al., 2014;Kebukawa et al., 2019). Each density layer was chemically combined during the sol-gel synthesis process, forming a single aerogel block with a large area of approximately 90 · 90 mm. ...
The Tanpopo experiment was the first Japanese astrobiology mission on board the International Space Station. It included exposure experiments of microbes and organic compounds as well as a capture experiment of hypervelocity impacting microparticles. We deployed three Exposure Panels, each consisting of 20 Exposure Units that contained microbes, organic compounds, an alanine UV dosimeter or an ionizing radiation dosimeter. The three Exposure Panels were situated on the zenith face of the Exposed Experiment Handrail Attachment Mechanism (ExHAM) that was pointing in zenith direction toward space, which was attached on a handrail of the Japanese Experiment Module (Kibo) Exposed Facility (JEM-EF) outside the International Space Station. The three Exposure Panels were one by one retrieved and returned to the ground after approximately 1, 2, and 3 years of exposure to the space environment. Capture Panels, each of which contained one or two blocks of amorphous silica aerogel, were exposed to collect hypervelocity impact microparticles. Possible captured particles may include micrometeoroids, human-made orbital debris, and natural terrestrial particles. Each year, Capture Panels containing from 11 to 12 aerogel blocks were attached to the three faces of the ExHAM (pointing to zenith, ram, and port); they remained in place for about 1 year and were then returned to the laboratory. This process was repeated three times, in total, during 2015-2018. Additional exposure of a Capture Panel facing ram was conducted between 2018 and 2019. Once the aerogel blocks were returned to the laboratory, they were encapsulated in dedicated transparent plastic cases and optically inspected by a specially designed microscopic system. Once located and recorded, hypervelocity impact signatures were excavated one by one and distributed for further detailed analyses. The apparatus, operation, and environmental factors of all the Tanpopo experiments are summarized in this article.
... Thermal alteration is considered to be the main cause of change in organic contents due to the impact shock heating reaching up to a few thousand degrees Celsius (Hörz et al., 2009). The general track model implies that organic molecules deposited on the impact track will be exposed to high temperature flash heating (Domínguez, 2009), while HIE with hydrated mineral grains showed that the mineralogical thermal alteration only occur on the projectile surface while interior remains unaltered with just 150 nm below the rim (Okudaira et al., 2004). Hence, the recovery rate of the organic molecules depends on their localization within the projectile (surface or interior) as well as the thermal history of the projectile immediately after the impact. ...
The in situ detection of organic molecules in space is key to understanding the variety and the distribution of the building blocks of life, and possibly the detection of extraterrestrial life itself. Gas chromatography mass spectrometry (GC-MS) has been the most sensitive analytical strategy for organic analyses in flight, and was used on missions from NASA's Viking, Phoenix, Curiosity missions to ESA's Rosetta space probe. While pyrolysis GC-MS revealed the first organics on Mars, this step alters or degrades certain fragile molecules that are excellent biosignatures including polypeptides, oligonucleotides and polysaccharides, rendering the intact precursors undetectable. We have identified a solution tailored to the detection of biopolymers and other biomarkers by the use of liquid-based capillary electrophoresis and electrochromatography. In this study, we show that a capillary electrochromatography approach using monolithic stationary phases with tailor-made surface chemistry can separate and identify various polycyclic aromatic hydrocarbons, nucleobases and aromatic acids that could be formed under astrophysically relevant conditions. In order to simulate flyby organic sample capture, we conducted hypervelocity impact experiments which consisted of accelerating peptide-soaked montmorillonite particles to a speed of 5.6 km s ⁻¹ , and capturing them in an amorphous silica aerogel of 10 mg cm ⁻³ bulk density. Bulk peptide extraction from aerogel followed by capillary zone electrophoresis led to the detection of only two stereoisomeric peptide peaks. The recovery rates of each step of the extraction procedure after the hypervelocity impact suggest that major peptide loss occurred during the impact. Our study provides initial exploration of feasibility of this approach for capturing intact peptides, and subsequently detecting candidate biomolecules during flight missions that would be missed by GC-MS alone. As the monolith-based electrochromatography technology could be customized to detect specific classes of compounds as well as miniaturized, these results demonstrate the potential of the instrumentation for future astrobiology-related spaceflight missions.
... Collaboration with FIB and TEM laboratories at LLNL showed the extent of alteration, including survival of original crystalline structure, but loss of volatile elements [30,31,32,33]. Experiments in Kent and in Japan, using hydrated silicate minerals showed portions of coarser grains (> 2 µm) survive in long, narrow aerogel tracks, but their surface was denatured by interaction with surrounding hot, compressed aerogel [34,35,36]. Earlier studies had shown phyllosilicates can survive aerogel capture [37], but the lower size limit for preservation now suggested a potential bias against recognition of these diagnostic minerals, whose presence might indicate processes involving liquid water during the comet history, as suspected from discovery of distinctive Ni-and Cu-bearing sulfides [38]. ...
In the last two decades, experimental hypervelocity impacts (HVI) using light gas gun (LGG) shots have answered numerous questions about how comet dust can be captured, and have repeatedly provided explanations for phenomena encountered during study of samples returned from comet Wild 2 by the NASA JPL-Caltech Stardust mission. LGG experiments were carried out in several laboratories, especially in NASA, in Japan, and at the University of Kent (Canterbury, UK). Analogue materials were produced for testing and calibration of novel and diverse microanalysis methods in research institutions around the world. Impact tracks on low density silica aerogel and craters on Al alloy foils gave calibration in determination of size and composition for Wild 2 particles, and experimental HVI features revealed how internal grain size and structure of comet dust grains can be interpreted from detailed shapes of impact structures. Firing of analogue mineral materials helped us to understand how specific mineral components are preserved, how crystal structure and composition are altered during capture, and how this may limit interpretation of collected grains. In this review, I explain the range of studies performed so far, and suggest new experiments are needed to help understand: preservation, alteration and loss of subtle internal grain structures; modification of elemental and isotopic signatures in relatively fragile materials (e.g. organic matter); and the size of particles making bulbous aerogel tracks.
... The neoformed silicates retain the flaky morphologies of the original phyllosilicates, however, and so are still recognizable as transformed phyllosilicates. Okudaira et al. (2004Okudaira et al. ( , 2006 launched phyllosilicates (serpentine and cronstedtite) into aerogel at velocities of 4 and 6.1 km s −1 , and saw preservation of a significant fraction. Additional evidence that some phyllosilicates would have survived capture is presented by the partial survival of scattered, delicate, low-temperature phases among the Wild 2 samples-fine-grained, organic-rich phases with deuterium and 15 N excesses (Sandford et al. 2006;Cody et al. 2007). ...
... The bottom picture in Fig. 3 is the aerogel holder. 7) As for the target material, two aerogel test pieces are basically placed in the target chamber top to bottom: one is aerogel without heating (Type A) and the other is one after the arcjet heating test (Type B). From the point of view of thermal decomposition, the feasibility study of sampling can be improved by carrying out the capture simulation during silica aerogel heating. ...
A Mars Aero-flyby Sample Collection (MASC) mission has been proposed in a Mars exploration project at Japan Aerospace Exploration Agency (JAXA). The MASC vehicle enters the Martian atmosphere, captures dust particles and atmospheric gases at sampling altitudes between 30 and 50 km, and returns back to Earth. In order to improve the feasibility of this project, the development of its sampling system during flying in the Martian dusty atmosphere is crucial. Since silica aerogel has been used as a capturing medium for micrometeoroids and space debris, it is also planned to be used for the MASC mission. However, the capture of hypervelocity micron-size dust particles during the Martian atmospheric flight using aerogel is challenging. The aerogel is exposed to significant aerodynamic heating during sampling, and thus, the effect of heated aerogel on the dust particles must be evaluated. This work attempts to evaluate the impact on aerogel and the survivability of the dust particles inside the capturing medium by carrying out light gas gun and Van de Graaff experimental tests. By comparing the cases between normal and heated aerogels, the survivability of the dust samples as well as the heating effect has been investigated.
... This is because it is usually difficult to find and collect sub-m-sized particles captured in aerogel. According to the previous results of the laboratory experiments on hypervelocity impacts 9,10,16,24) , hydrous silicates, carbonates, NH 3 -bearing materials, and refractory organic matter will be able to collect without significant thermal alterations during capturing in type 2 mission (i.e., sampling velocity of ~4 km/s) ( Table 2). In type 3 (i.e., sampling velocity of ~0.2 km/s), even soluble organic matter, including life-related organic materials, also could collect without significant alterations with the metallic plate collector ( Table 2). ...
Enceladus is the only icy satellite known to exhibits on-going geological activity of water-rich plumes derived from the interior ocean. Here, we propose a sample return and in-situ measurement mission for Enceladus' plume materials. Depending on the cost, mission duration, and propulsion system, we propose three types of missions to Enceladus; type 1: free-return trajectory, type 2: trajectory orbiting Saturn, and type 3: trajectory orbiting Enceladus. Type 2 and 3 are preferable to type 1 in order to achieve lower encountering velocity to the plumes (> 4 km/s and 0.2 km/s for type 2 and 3, respectively) and, thus, to collect multiple and intact samples. High resolution mass spectroscopy of the gas components will provide essential information to understand the physical and chemical conditions of both the interior ocean and the solar nebula. Furthermore, detailed onboard and onshore analyses of returned samples could provide geochemical, preboplogical, and, potentially, biological context in the interior ocean of Enceladus.
... However, the highest temperature pulses were short in duration and destruction of all phyllosilicates would not be expected if they were present in large amounts (patches several microns or so in size). Several studies of shots of phyllosilicates using light-gas guns and launch velocities equal to or greater than 6.1 kms )1 have shown conclusively that some low temperature phyllosilicates will survive (Okudaira et al. 2004Zolensky et al. 2008), particularly in grains >1 lm in size (Noguchi et al. 2007). Thus, we would expect that bulbous tracks excavated by impactors which were composed of phyllosilicate-rich materials and that were several to tens of microns in size should have some preserved phyllosilicates and this is not observed. ...
Transmission electron microscopy examination of 87 large fragments from
16 carrot-shaped and bulbous Stardust (SD) tracks was performed to study
the range and diversity of materials present in comet Wild 2. Olivines
and low-Ca pyroxenes represent the largest proportions of fragments
observed; however, a wide range of minerals and rocks were found
including probable ferromagnesian, Al-rich and Si-rich chondrule
fragments, a refractory inclusion, possible matrix mineral/lithic
clasts, and probable condensate minerals. These materials, combined with
fine-grained components in the tracks, are analogous to components in
unequilibrated chondrite meteorites and cluster interplanetary dust
particles (IDPs). Two unusual lithologies in the bulbous tracks are only
observed in chondritic porous IDPs and may have direct links to IDPs.
The absence of phyllosilicates indicates that comet Wild 2 may be a
"dry" comet that did not accrete or form significant amounts of hydrated
phases. Some large mineral fragments in the SD tracks are analogous to
large mineral IDPs. The large variations of the coarse-grained
components within and between all 16 tracks show that comet Wild 2 is
mineralogically diverse and unequilibrated on nearly all scales and must
have accreted materials from diverse source regions that were widely
dispersed throughout the solar nebula.
... Only one issue that has to be considered is a possible modification of the chemical composition of organic matter in IDPs upon their high velocity impact to the aerogel. This issue has been also concerned in the Stardust cometary dust sample return mission, and principally the possible alteration of minerals has been investigated 15,16) . Via the laboratory simulations of hypervelocity capture by using light-gas guns to impact into aerogels, it has been suggested that the interior of > 4 µm across residual grains containing abundant materials that inhibit temperature rise would have not experienced > 300 °C at the center 16) . ...
We are planning to collect interplanetary dust particles (IDPs) at the Exposure Facility of Japan Experimental Module (JEM: KIBO) of the International Space Station (ISS), as one of subthemes in Tanpopo mission. The advantage of collecting IDPs at Low Earth Orbit is that loss and/or changes of the intact IDPs compositions due to atmospheric entry heating and terrestrial contamination will be avoided. After collecting and returning the IDPs to the Earth, organic chemistry, isotope compositions, mineralogy and impact-track morphology of the samples will be analyzed by the state-of-art analytical techniques. Low-density silica aerogel (0.01 g/cm<sup>3</sup>) will be used as a capture material for minimizing the damage of IDPs upon their high velocity impact. In order to evaluate the performance of the aerogel, as a ground-based experiment, we have conducted a laboratory experiment of aerogel capture of Murchison meteorite powder using a two-stage light gas gun at ISAS. Infrared spectroscopic imaging has revealed that organic carbon is survived in the shot meteorite grain. In addition, Raman spectra of the shot and pre-shot samples are very similar, indicating that aromatic structures which are a major part of meteoritic organic matter is not modified at the impact velocity of 4 km/s.
... An attempt to introduce heavy metal such as Pb into aerogel without decreasing the transparency is under way. The aerogel with extremely low density will be employed as a cosmic dust collector [8]. To catch cosmic dusts softly, aerogel with as low density as possible is required. ...
New production methods of silica aerogel with high and low refractive indices have been developed. A very slow shrinkage of alcogel at room temperature has made possible producing aerogel with high refractive indices of up to 1.265 without cracks. Even higher refractive indices than 1.08, the transmission length of the aerogel obtained from this technique has been measured to be about 10 to 20 mm at 400 nm wave length. A mold made of alcogel which endures shrinkage in the supercritical drying process has provided aerogel with the extremely low density of 0.009 g/cm<sup>3</sup>, which corresponds to the refractive index of 1.002. We have succeeded producing aerogel with a wide range of densities.
... The use of aerogel for the capture of hypervelocity fine particles began in the mid-1990s and was based on work done using low density foams (Tsou and Albee 1988;Tsou 1990Tsou , 1995Zolensky et al. 1990). Since that time many groups have carried out extensive studies of the effectiveness of aerogels as hypervelocity capture media (Burchell et al. 1999;Ho¨rz et al. 2000;Kitazawa et al. 1999;Okudairi et al. 2004). The Stardust mission, which was launched in 1999, traveled to comet Wild 2, collected particles from the coma of the comet in low-density silica aerogel, and returned the samples to Earth in 2006 (Brownlee et al. 1996Tsou et al. 2003). ...
Abstract– The Stardust sample return mission to the comet Wild 2 used silica aerogel as the principal cometary and interstellar particle capture and return medium. However, since both cometary dust and interstellar grains are composed largely of silica, using a silica collector complicates the science that can be accomplished with these particles. The use of non-silica aerogel in future extra-terrestrial particle capture and return missions would expand the scientific value of these missions. Alumina, titania, germania, zirconia, tin oxide, and resorcinol/formaldehyde aerogels were produced and impact tested with 20, 50, and 100 μm glass microspheres to determine the suitability of different non-silica aerogels as hypervelocity particle capture mediums. It was found that non-silica aerogels do perform as efficient hypervelocity capture mediums, with alumina, zirconia, and resorcinol/formaldehyde aerogels proving to be the best of the materials tested.
... these tracks by their relative masses yields a bulk Wild 2 crystalline silicate fraction of Fe-bearing minerals. However, hypervelocity capture of cometary grains into aerogel may convert crystalline phases to amorphous phases (see, e.g., Okudaira et al. 2004), though the reverse process is unexpected because of the short time scale for capture. Concerning the latter point, we saw no evidence of crystalline silicates in the tracks of basalt glass projectiles shot into aerogel at speeds close to the Stardust capture velocity (Marcus et al. 2008). ...
Abstract— Using X-ray microprobe analysis of samples from comet Wild 2 returned by the Stardust mission, we determine that the crystalline Fe-bearing silicate fraction in this Jupiter-family comet is greater than 0.5. Assuming this mixture is a composite of crystalline inner solar system material and amorphous cold molecular cloud material, we deduce that more than half of Wild 2 has been processed in the inner solar system. Several models exist that explain the presence of crystalline materials in comets. We explore some of these models in light of our results.
In a consortium analysis of a large particle captured from the coma of comet 81P/Wild 2 by the Stardust spacecraft, we report the discovery of a field of fine‐grained material (FGM) in contact with a large sulfide particle. The FGM was partially located in an embayment in the sulfide. As a consequence, some of the FGM appears to have been protected from damage during hypervelocity capture in aerogel. Some of the FGM particles are indistinguishable in their characteristics from common components of chondritic‐porous interplanetary dust particles, including glass with embedded metals and sulfides and equilibrated aggregates. The sulfide exhibits surprising Ni‐rich lamellae, which may indicate that this particle experienced a long‐duration heating event after its formation but before incorporation into Wild 2.
Due to its extremely high porosity and the nanoscale filaments that make up its structure, aerogel is an excellent material for the capture of hypervelocity, micron-sized particles. A great deal of the kinetic energy of a particle is converted to thermal energy during the capture process, altering or even destroying components of the particle. The studies described here were conducted using aggregate projectiles made up of magnetic sub-micron hematite particles in an attempt to directly measure the temperatures experienced by fine particles during hypervelocity capture in aerogels. When these particles are heated to a temperature above their Curie temperature (675°C) during the capture, they lose their magnetization. Thus, by impact testing these particles in aerogels at different velocities, we were able to determine if individual components of these aggregate particles were heated to a temperature greater than their Curie temperature by observing their magnetization. After impact testing, the particles were extracted from the aerogel, thin sectioned, and observed using atomic and magnetic force microscopy, as well as, electron paramagnetic resonance. Terminal particles for impacts at or above 4.5 km/sec were still magnetic, while those from the track walls were not. Even terminal particles captured at 6.6 km/sec were still magnetic. Iron oxide particles coated with silica, to mimic extraterrestrial materials, from track walls captured at 5.47 km/sec were still magnetic. The study also demonstrated that aggregate projectiles can survive the forces they are subjected to during hypervelocity launch in a light gas gun.
Abstract– Impacts of small particles of soda-lime glass and glycine onto low density aerogel are reported. The aerogel had a quality similar to the flight aerogels carried by the NASA Stardust mission that collected cometary dust during a flyby of comet 81P/Wild 2 in 2004. The types of track formed in the aerogel by the impacts of the soda-lime glass and glycine are shown to be different, both qualitatively and quantitatively. For example, the soda-lime glass tracks have a carrot-like appearance and are relatively long and slender (width to length ratio <0.11), whereas the glycine tracks consist of bulbous cavities (width to length ratio >0.26). In consequence, the glycine particles would be underestimated in diameter by a factor of 1.7–3.2, if the glycine tracks were analyzed using the soda-lime glass calibration and density. This implies that a single calibration for impacting particle size based on track properties, as previously used by Stardust to obtain cometary dust particle size, is inappropriate.
Abstract— Suessite along with hapkeite and more Fe-rich iron-silicides up to Fe7Si2 formed near the entrance of aerogel track #44. These phases are ˜100 nm, quenched-melt spheres, but the post-impact cooling regime was such that melt vitrification produced a poly cry stalline mixture of Fe silicides and kamacite. The compositional similarities of the impact-produced Fe-Si phases and the Fe-Ni-S phases scattered throughout the aerogel capture medium strongly supports the idea that Fe silicides resulted from a reaction between molten Fe-Ni-S phases and aerogel at very high heating and cooling rates. Temperatures of around 1500 °C are inferred from the observed compositions had the silicide spheres formed at thermodynamic equilibrium, which seems unlikely. When the conditions were kinetically controlled, they could have been similar to those leading to the formation of solids with predictable deep metastable eutectic compositions in laboratory condensation experiments.
Abstract— We compare the observed composition ranges of olivine, pyroxene, and Fe-Ni sulfides in Wild 2 grains with those from chondritic interplanetary dust particles (IDPs) and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular. Wild 2 olivine has an extremely wide composition range, from Fa0–96, with a pronounced frequency peak at Fa1. The composition range displayed by the low-calcium pyroxene is also very extensive, from Fs48 to Fs0, with a significant frequency peak centered at Fs5. These ranges are as broad or broader than those reported for any other extraterrestrial material. Wild 2 Fe-Ni sulfides mainly have compositions close to that of FeS, with less than 2 atom% Ni; to date, only two pentlandite grains have been found among the Wild grains, suggesting that this mineral is not abundant. The complete lack of compositions between FeS and pentlandite (with intermediate solid solution compositions) suggests (but does not require) that FeS and pentlandite condensed as crystalline species, i.e., did not form as amorphous phases, which later became annealed. While we have not yet observed any direct evidence of water-bearing minerals, the presence of Ni-bearing sulfides, and magnesium-dominated olivine and low-Ca pyroxene does not rule out their presence at low abundance. We do conclude that new investigations of major- and minor- element compositions of chondrite matrix and IDPs are required.
Cometary dust is a heterogeneous mixture of unequilibrated olivine and pyroxenes, amorphous silicates, Fe-Ni sulfides, and minor amounts of oxides and other minerals. While forsterite Mg2SiO4 and enstatite MgSiO3 are the most common silicate minerals, both the olivine and pyroxenes also show a wide range in Mg/Fe in at least some comets. Carbon in the dust is enriched relative to CI chondrites; a significant fraction of the carbon is in the form of organic refractory material. The return of the particulate sample from ecliptic comet 81P/Wild 2 has opened up a new window for revealing the dust mineralogy at a level of detail not previously possible. The most interesting result from the Wild 2 sample to date is the discovery of refractory calcium aluminum-rich inclusions (CAI) similar to those found in primitive meteorites; chondrule fragments are also present.
Comets formed in the outer parts of the solar nebula where temperatures remained low enough so that interstellar grains could have survived. The small glassy silicates in comets may indeed be interstellar grains. The CAI and the widespread, abundant crystalline silicates must have condensed in the hot inner solar nebula; their presence in comets is evidence for strong radial mixing in the solar nebula. The preponderance of Mg-rich silicates has a natural explanation in the condensation sequence; they are the first to condense in a hot gas and only react with iron at lower temperatures.
This review discusses the mineralogy of cometary dust determined from infrared spectroscopy, in situ Halley measurements, IDPs, and the captured particles from comet Wild 2.
The NASA Stardust mission has provided for laboratory study an extensive data set of cometary dust of known provenance (from comet 81P/Wild 2) yielding detailed insights into the composition of the comet. Combined with the results of data from other missions to short-period Jupiter family comets (JFC), this has greatly deepened the understanding of such objects. If depressions on the surface of comet 81P/Wild 2 are all taken as evidence of impact cratering, their number suggests a long occupancy in the outer region of the Solar System. The dust from comet 81P/Wild 2 has been shown to be heavily deficient in pre-Solar grains and rich in materials formed at high temperatures in the inner Solar System. Although it is too early to know if this is typical of JFC, it does argue for rapid and thorough mixing of materials in the disk on timescales related to comet formation, and may also suggest outward migration of small icy bodies after their formation. Thus, instead of providing mainly new knowledge of the pre-Solar materials expected to be rich in comets, Stardust and comet 81P/Wild 2 have instead focussed attention on large-scale transport processes during the critical period when cometary parent bodies were forming in the early Solar System.
Capture of high-speed (hypervelocity) particles in aerogel at ambient temperatures of 175–763 K is reported. This extends previous work which has mostly focussed on conducting experiments at ambient laboratory temperatures, even though aerogels are intended for use in cosmic dust capture cells in space environments which may experience a range of temperatures (e.g., the NASA Stardust mission which collected dust at 1.81 AU and putative Mars atmospheric sampling missions). No significant change in track length (normalised to impactor size) was found over the range 175–600 K, although at 763 K a significant reduction (30%) was found. By contrast, entrance hole diameter remained constant only up to 400 K, above this sudden changes of up to 50% were observed. Experiments were also carried out at normal laboratory temperature using a wide range of aerogel densities and particle sizes. It was found that track length normalised to particle size varies inversely with aerogel density. This is a power law dependence and not linear as previously reported, with longer tracks at lower densities. Glass projectiles (up to 100 μm size) were found to undergo a variety of degrees of damage during capture. In addition to the well known acquisition of a coating (partial or complete) of molten aerogel the mechanical damage includes pitting and meridian fractures. Larger (500 μm diameter) stainless steel spheres also showed damage during capture. In this case melting and ablation occurs, suggesting surficial temperatures during impact in excess of 1400 °C. The response of the aerogel itself to passage of particles through it is reported. The presence of fan-like fractures around the tracks is attributed to cone cracking similar to that in glasses of normal density, with the difference that here it is a repetitive process as the particles pass through the aerogel.
Aims. We attempt to ellucidate the structure and chemical composition of the carbon bulk detected in cometary Stardust particles. We determine if the carbon material observed spectroscopically is of true cometary origin and whether or not it was formed by direct UV-photoprocessing of icy grain mantles in the local dense cloud and/or the solar nebula.Methods. We acquire infrared spectroscopy of ten Stardust cometary particles from track 35 and the aerogel inside and outside the particle track. Using infrared and Raman spectroscopy, the dominant carbon component in cometary Stardust particles was compared to IDPs and organics made from UV-photoprocessing of interstellar/circumstellar ice analogs in the laboratory. The Raman spectra of Stardust particles used in this comparison are adapted from the literature.Results. As indicated in previous works, it is found that the collecting aerogel medium, processed during particle impact, poses serious problems for the infrared analysis of the Stardust cometary particles reported in this paper. We identify the structure of the carbon bulk of the organic material retrieved from the aerogel with a form of (hydrogenated) amorphous carbon. It is found that this material is not a direct product of ice photoprocessing.
Impact experiments using silica aerogel as a deceleration and capture medium for interplanetary dust are reported. A rough correlation is noted between increasing particle track lengths and decreasing aerogel density, and there is a poor correlation of track lengths with impact velocity at laboratory attainable velocities of 5-7 km/s. It is concluded that aerogel track lengths should not be used as velocity indicators. Chemical analyses are also reported of aerogel samples used in this study in order to assess the risks concerning contamination of interplanetary dust particles by the silica aerogel capture medium. It is demonstrated that this material is impressively clean.
Laboratory hypervelocity impact experiments were conducted to verify the performance of aerogel dust collectors used for gathering meteoroids and space debris in the near-Earth environment and to derive the relationships of various parameters characterizing the projectile with morphology of tracks left by the penetrating projectile in the aerogel collector pad. Silica aerogel collectors of 0.03 g/cm3 density were impacted at velocities ranging from 1 to 14 km/s with projectiles of aluminum oxide, olivine, or sodalime glass, with diameters ranging from 10 to 400 mum. At impact velocities below 6 km/s the projectiles were captured without fragmentation by the aerogel collector and, in many instances, without complete ablation even at 12 km/s. The shapes and dimensions of the penetration tracks left in the aerogel collector were correlated with the impact parameters, and the results permitted derivation of a series of equations relating the track dimensions to incoming projectile size, impact energy, and other projectile parameters. A simplified model, similar to meteor-entry phenomena, was used to predict the trends in experimental penetration track lengths and the diameters of captured projectiles.