Exposure of the Hubble Space Telescope to space in low Earth orbit resulted in numerous hypervelocity impacts by cosmic dust (micrometeoroids) and anthropogenic particles (orbital debris) on the solar arrays and the radiator shield of the Wide Field and Planetary Camera 2, both subsequently returned to Earth. Solar cells preserve residues from smaller cosmic dust (and orbital debris) but give less reliable information from larger particles. Here, we present images and analyses from electron, ion and X-ray fluorescence microscopes for larger impact features (millimetre- to centimetre-scale) on the radiator shield. Validated by laboratory experiments, these allow interpretation of composition, probable origin and likely dimensions of the larger impactors. The majority (~90%) of impacts by grains greater than 50 μm in size were made by micrometeoroids, dominated by magnesium- and iron-rich silicates and iron sulfides, metallic iron-nickel and chromium-rich spinel similar to that in ordinary chondrite meteorites of asteroid origin. Our re-evaluation of the largest impact features shows substantially fewer large orbital debris impacts than reported by earlier authors. Mismatch to the NASA ORDEM and ESA MASTER models of particle populations in orbit may be partly due to model overestimation of orbital debris flux and underestimation of larger micrometeoroid numbers. This article is part of the theme issue ‘Dust in the Solar System and beyond’.

Observation of dust and debris in the near Earth environment is a field of great commercial and scientific interest, vital to maximising the operational and commercial life-cycle of satellites and reducing risk to increasing numbers of astronauts in Low Earth Orbit (LEO). To this end, monitoring and assessment of the flux of particles is of paramount importance to the space industry and wider socio-economic interests that depend upon data products/services from orbital infrastructure. We have designed a passive space dust detector to investigate the dust environment in LEO—the Orbital Dust Impact Experiment (ODIE). ODIE is designed for deployment in LEO for ∼1 year, whereupon it would be returned to Earth for analysis of impact features generated by dust particles. The design emphasises the ability to distinguish between the orbital debris (OD) relating to human space activity and the naturally occurring micrometeoroid (MM) population at millimetre to submillimetre scales. ODIE is comprised of multiple Kapton foils, which have shown great potential to effectively preserve details of the impacting particles’ size and chemistry, with residue chemistry being used to interpret an origin (OD vs. MM). LEO is a harsh environment—the highly erosive effects of atomic oxygen damage Kapton foil—requiring the use of a protective coating. Common coatings available for Kapton (e.g., Al, SiO2, etc.) are problematic for subsequent analysis and interpretation of OD vs. MM origin, being a common elemental component of MM or OD, or having X-ray emission peaks overlapping with those of elements used to distinguish MM from OD. We thus propose palladium coatings as an alternative for this application. Here we report on the performance of palladium as a protective coating for a Kapton-based passive dust detector when exposed to atomic oxygen and impact. When subjected to impact, we observe that thicker coatings suffer delamination such that a coating of <50 nm is recommended. Analysis of atomic oxygen exposed samples shows a thin 10 nm coating of palladium significantly reduces the mass loss of Kapton, while coatings of 25 nm and over perform as well as or better than other commonly used coatings.

The origin of hypogene alteration and mineralization features in the Escondida porphyry Cu deposit resulted from intense overprinting related to three main hydrothermal stages. The beginning of each stage is recorded by deposition of bright quartz crystals on vein walls that precipitated from high-temperature fluids. In the deepest zones of the deposit, the earliest stage started with exsolution of intermediate-density fluids, which transported high concentrations of Cu, whereas Mo was not detected. However, in the shallow zones, the early stage began with depressurization and unmixing of intermediate-density fluids, which generated both a hypersaline and vapour-rich fluid phase, producing an important geochemical segregation between both phases. The transitional stage also started with circulation of intermediate-density fluids but never experienced unmixing. These fluids transported the highest Mo concentrations in the deposit; however, Cu displays lower concentrations relative to intermediate-density fluids from the early stage. The beginning of the late stage was also associated with intermediate-density fluids; however, Cu and Mo were below the detection limits in most of the analysed fluids. During the evolution of the three stages, the fluids experienced gradual cooling, which promoted the precipitation of euhedral and zoned quartz crystals that overgrew the early high-luminescence quartz generations. Sometimes, sulfide minerals display euhedral crystal boundaries with zoned quartz, suggesting that mineralization started during these phases. The latest events detected in each main stage are linked to cooler and low-salinity fluids, from which dark quartz and hypogene sulfides precipitated along microfractures and interstitial spaces developed in the earlier quartz generations.

The decade of the 2020s promises to be when humanity returns to space beyond Earth orbit, with several nations trying to place astronauts on the Moon, before going further into deep space. As part of such a programme, NASA and partner organisations, propose to build a Deep Space Gateway in lunar orbit by the mid-2020s. This would be visited regularly and offer a platform for science as well as for human activity. Payloads that can be mounted externally on the Gateway offer the chance to, amongst other scientific goals, monitor and observe the dust flux in the vicinity of the Moon. This paper looks at relevant technologies to measure dust which will impact the exposed surface at high speed. Flux estimates and a model payload of detectors are described. It is predicted that the flux is sufficient to permit studies of cometary vs. asteroidal dust and their composition, and to sample interstellar dust streams. This may also be the last opportunity to measure the natural dust flux near the Moon before the current, relatively pristine environment, is contaminated by debris, as humanity's interest in the Moon generates increased activity in that vicinity in coming decades. (C) 2021 COSPAR. Published by Elsevier B.V.

The fluence of dust particles < 10 micrometres in diameter was recorded by impacts on aluminium foil of the NASA Stardust spacecraft during a close fly-by of comet 81P/Wild 2 in 2004. Initial interpretation of craters for impactor particle dimensions and mass was based upon laboratory experimental simulations using >10 μm diameter projectiles and the resulting linear relationship of projectile to crater diameter was extrapolated to smaller sizes. We now describe a new experimental calibration programme firing very small monodisperse silica projectiles (470 nm to 10 μm) at ~ 6 km s -1 . The results show an unexpected departure from linear relationship between 1 and 10 μm. We collated crater measurement data and, where applicable, impactor residue data for 596 craters gathered during the post-mission preliminary examination (PE) phase. Using the new calibration, we recalculate the size of the particle responsible for each crater and hence reinterpret the cometary dust size distribution. We find a greater flux of small particles than previously reported. From crater morphology and residue composition of a sub-set of craters, the internal structure and dimensions of the fine dust particles is inferred and a ‘maximum-size’ distribution for the sub-grains composing aggregate particles is obtained. The size distribution of the small particles derived directly from the measured craters peaks at ~175 nm, but if this is corrected to allow for aggregate grains, the peak in sub-grain sizes is at <100 nm.

Monitoring dust particle populations in the vicinity of the Earth is vital to understand and mitigate against the hazards they pose to spacecraft, driving design of effective spacecraft shielding and optimum operational protocols. The flux of particles > few mm orbiting Earth has been investigated remotely using radar and optical telescopes [e.g. 1, 2], revealing that objects in this size range have increased in abundance rapidly since the dawn of the space age. Despite their diminutive size, objects smaller than the radar detection limit are still capable of significant damage to spacecraft. Such particles are expected to be far more numerous, with estimates in the trillions for the total number of particles >100 μm in size [3]. The degree of damage caused by these dust particles is heavily dependent on characteristics such as their relative velocity, impact angle, shape and composition, which vary as a function of origin (e.g. orbital debris originating from human activities in space have relative velocities that are typically slower than for natural micrometeoroids originating from comets and asteroids). It is therefore important to be able to distinguish between these two dust populations, to fully understand the threat posed by these particles. Previous flux measurements for smaller dust populations have largely been based on passive collection surfaces retrieved from dedicated missions, such as the long duration exposure facility (LDEF) [e.g. 4, 5], and opportunistic analyses of returned surfaces, such as solar cells and radiator panel from the Hubble Space Telescope [e.g. 6-9]. For many impact features it has been very time consuming, difficult or even impossible to give unambiguous attribution of particle origin due to the nature of the collection surface. Consequently, we lack significant and important information for both populations, but especially orbital debris. Whilst there is general agreement as to particle origins between studies of smaller grain sizes impacted on different surfaces [e.g. 7, 9], despite efforts [e.g. 9, 10], the origins for those impact features between 200 μm and 2 mm in size remains ambiguous – hence there remains uncertainty as to how to fill an important gap in our knowledge of the particle population. The Orbital Dust Impact Experiment (ODIE) is a dedicated, passive dust collector that we have designed to verify and understand the flux and origins of these particles. By exposing in low Earth orbit for a period of at least 1 year and returning to Earth for analysis, it will enable the unambiguous identification of both micrometeoroid and orbital debris particles over size ranges including 200 μm to 2 mm. This paper introduces our design and potential deployment options, as well as details of the analyses that would need to be performed upon its return.

Over the last decade, silica aerogel tracks and aluminum foil craters on the Stardust collector have been studied extensively to determine the nature of captured cometary dust grains. Analysis of particles captured in aerogel has been developed to a fine art, aided by sophisticated preparation techniques, and yielding revolutionary knowledge of comet dust mineralogy. The Stardust foil craters can be interpreted in terms of impacting particle size and structure, but almost all studies of composition for their contents have relied on in situ analysis techniques or relatively destructive extraction of materials. This has limited their examination and interpretation. However, numerous experimental hypervelocity impact studies under Stardust‐Wild 2 encounter conditions have shown that abundant dust components are preserved in foil craters of all sizes. Using some of these analogue materials, we have previously shown that modern, nondestructive scanning electron microscope imaging and X‐ray microanalysis techniques can document distribution of dust remnants both quickly and thoroughly within foil craters prior to any preparation. Here we present findings from our efforts to quantify the amount of residue and demonstrate a simple method of crater shape modification which can bring material into positions where it is much more accessible for in situ analysis, or safe removal of small subsamples. We report that approximately 50% of silicate‐dominated impactors were retained as impact crater residue; however, <3% of organic impactors remained in the craters after impact.

We report the mineralogy, petrology, major, minor and trace element geochemistry, O and Si isotopes of a complex compound chondrule from the Allende meteorite. The chondrule contains zones of refractory (Ca, Al-rich) regions along with regions more similar to ferromagnesian chondrules. The bulk silicon isotopic composition of the object is δ30Si = –0.71 ± 0.03‰. The oxygen isotopic composition of the different phases within the compound chondrules fall along the Allende chondrule line and range from Δ17O – 12.5 to –2‰. Rare earth element abundances are enriched compared to chondritic levels by up to 15× CI, and show a nebular condensate signature with depletions in Eu and Yb. Our data show that the object evolved in oxygen isotopes in a nebular environment, most likely due to formation from a mixture of diverse components combined with interaction with nebular gas. In addition, differences in olivine composition across the inclusion suggest isotopically distinct oxygen regions also existed in dust in the protoplanetary disk. This object and other compound objects demonstrate that CAIs were present in the chondrule forming region, however they are not found in the majority of chondrules. We speculate that the bulk of the CAIs may have been added into the CV parent body after initial accretion of the body.

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.

Return of materials from the Hubble Space Telescope (HST) during shuttle orbiter service missions has allowed inspection of large numbers of hypervelocity impact features from long exposure at about 615 km altitude in low Earth orbit (LEO) [1,2]. Here we describe the application of advanced X-ray microanalysis techniques on scanning electron microscopes (SEM), microprobes and a 2 MV Tandetron, to nearly 400 impacts on the painted metal surface of the Wide Field and Planetary Camera 2 (WFPC2) radiator shield [3,4]. We identified artificial Orbital Debris (OD) and natural Micrometeoroid (MM) origins for small [5] and even for larger particles [6], which usually may leave little or no detectable trace on HST solar arrays, as they penetrate through the full cell thickness [2,7].

Jorgkellerite, ideally Na3Mn3+ (3)(PO4)(2)(CO3)O-2 center dot 5H(2)O, is a new layered phosphate-carbonate from the Oldoinyo Lengai volcano in the Gregory Rift (northern Tanzania). The mineral occurs as spherulites, up to 200 mu m in diameter, consisting of plates up to 10 mu m in thickness in shortite-calcite and calcite carbonatites. Jorgkellerite is brown with a vitreous lustre and has a perfect micaceous cleavage on {001}, Mohs hardness is 3. The calculated density is 2.56 g/cm(3). Jorgkellerite is uniaxial (-), omega = 1.700(2), epsilon = 1.625(2) (Na light, 589 nm) with distinct pleochroism: O = dark brown, E = light brown. The empirical formula of the mineral (average of 10 electron microprobe analyses) is (Na2.46K0.28Ca0.08Sr0.04Ba0.02)(Sigma 2.88)(Mn3+ Fe-2.39(3+) (0.56))(Sigma 2.95)((PO4)(1.95)(SiO4)(0.05)))(Sigma 2.00)(CO3)(O-1.84(OH)(0.16))(Sigma 2.00)center dot 5H(2)O. The oxidation state of Mn has been determined by XANES. Jorgkellerite is trigonal, space group P-3, a = 11.201(2) , c = 10.969(2) angstrom, V = 1191.9(7) angstrom(3) and Z = 3. The five strongest powder-diffraction lines [d in angstrom, (I/I-o), (hkl)] are: 10.970 (100) (001), 5.597 (15) (002), 4.993 (8) (111), 2.796 (14) (220) and 2.724 (20) (004). The crystal structure is built up of the layers composed of disordered edge-sharing [MnO6] octahedra. Each fourth Mn site in octahedral layer is vacant that results in appearance of ordered system of hexagonal "holes" occupied by (CO3) groups. The overall composition of the layer can be expressed as [Mn3O8(CO3)]. These manganese-carbonate layers are linked in the third dimension by (PO4) tetrahedra and Na-polyhedra. The origin of jorgkellerite is related to low-temperature oxidative alteration of gregoryite-nyerereite carbonatites.

Jörgkellerite, ideally Na3Mn3+ 3(PO4)2(CO3)O2·5H2O, is a new layered phosphate-carbonate from the Oldoinyo Lengai volcano in the Gregory Rift (northern Tanzania). The mineral occurs as spherulites, up to 200 μm in diameter, consisting of plates up to 10 μm in thickness in shortite-calcite and calcite carbonatites. Jörgkellerite is brown with a vitreous lustre and has a perfect micaceous cleavage on {001}, Mohs hardness is 3. The calculated density is 2.56 g/cm3. Jörgkellerite is uniaxial (-), ω = 1.700(2), ε = 1.625(2) (Na light, 589 nm) with distinct pleochroism: O = dark brown, E = light brown. The empirical formula of the mineral (average of 10 electron microprobe analyses) is (Na2.46K0.28Ca0.08Sr0.04Ba0.02)Σ2.88(Mn3+ 2.39Fe3+ 0.56)Σ2.95((PO4)1.95(SiO4)0.05))Σ2.00(CO3)(O1.84(OH)0.16)Σ2.00·5H2O. The oxidation state of Mn has been determined by XANES. Jörgkellerite is trigonal, space group P-3, a = 11.201(2) Å, c = 10.969(2) Å, V = 1191.9(7) Å3 and Z = 3. The five strongest powder-diffraction lines [d in Å, (I/I o), (hkl)] are: 10.970 (100) (001), 5.597 (15) (002), 4.993 (8) (111), 2.796 (14) (220) and 2.724 (20) (004). The crystal structure is built up of the layers composed of disordered edge-sharing [MnO6] octahedra. Each fourth Mn site in octahedral layer is vacant that results in appearance of ordered system of hexagonal “holes” occupied by (CO3) groups. The overall composition of the layer can be expressed as [Mn3O8(CO3)]. These manganese-carbonate layers are linked in the third dimension by (PO4) tetrahedra and Na-polyhedra. The origin of jörgkellerite is related to low-temperature oxidative alteration of gregoryite-nyerereite carbonatites.

Introduction: Studies of experimental Stardust analogue craters from projectiles impacted onto aluminium foil have shown dependence of crater ellipticity and rim morphology on projectile size, shape, velocity and trajectory [1]. When particles impact perpendicular to the target, residue can be found throughout the bowl shape [2], and as much as ~55 % of the impacting particle can be preserved [3]. Here we show how novel energy-dispersive X-ray spectroscopy (EDX) reveals more information as to preservation, modification and distribution of impact residue. Method: Light gas gun shots at the University of Kent fired 22 μm soda lime glass projectiles onto 100 μm thick Al 1100 foil targets at ~6 km/s. EDX images of craters with different impact angles were acquired using an annular Bruker silicon drift detector (SDD) on an FEI Quanta field emission scanning electron microscope. To enhance spatial resolution for element analysis, revealing features <100 nm in size, low acceleration voltage (9 kV and 2.6 kV) were applied. Results: The oblique impacts show an uneven crater floor with multiple steps in the downrange direction. The maps show a link between distribution of impact residues and impact angle. As the impact angle departs from perpendicular, the residue distributions initially appear to shift so that they are concentrated in the downrange direction of the crater. The crater surface shows that both the silicate projectile residue and aluminium target have characteristic flow textures, the silicate showing filaments which resembles a Pele’s hair type morphology. At crater steps, aluminium also grades into elongated filaments in the downrange direction. Both components have clearly undergone melting. Previous work using focused ion beam sectioning and transmission electron microscopy [4] has demonstrated intimate mixing and compositional blending between impactor and aluminium deeper within melt layers during impact. The presence of micrometre-scale aluminium blebs on top of silicate melt (Fig. 1) suggests that in the latest stages of melt movement, the two melts were essentially immiscible, and aluminium with a flow like morphology was deposited on top of already solidifying silicate melt.

Introduction: Lunar meteorite Lynch 002 was discovered in Western Australia in 2010 [1]. Only two abstracts providing general petrography and bulk O isotope data [1] and bulk/trace element neutron activation data [2] have been published to date about this sample. Here, we present preliminary data from a more comprehensive study of Lynch 002. Lynch 002 is a fine-grained, complex regolith breccia that has experienced some terrestrial alteration [1,2]. Based on the fine grain size and the presence of glass spherules and agglutinates [1], it likely formed from relatively mature regolith. Korotev [2] noted that it is rich in Fe for a brecciated meteorite (~9 wt.%) and unusually rich in light rare earth elements. Lynch 002 contains many lithic fragments including mare basalts, KREEP-rich material, and feldspathic material, as well as remnants of pyroxferroite [1]. Other important features of Lynch 002 include melt veins cutting through the sample, and cracks infilled by terrestrial carbonate [1]. For this work we focus primarily on the basaltic clasts, but mineral fragments are also abundant [1]. Mare basalt clasts: Lynch 002 contains several basalt fragments with a variety of sizes and textures. All are small (< ~500 m). We report preliminary mineralogical data from eight mare basalt clasts (Lithics 1, 4, 5, 8, 11, 12, 20, and 33) here. These basalts range in size from ~100 to ~500 m. Most have subophitic textures with strongly zoned pyroxenes, although another fragment (Lithic 12, Fig. 1B) has an olivine phyric texture (though this could be a recrystallized impact melt). Grain sizes vary from 100+ m long in Lithic 1 and 11 (Fig. 1C, D), to < 20m in Lithics 5 and 12. Lithic 1 is unusual in that about ~20 % of the clast consists of elongate silica grains (Fig. 1C), though silica is found in several of the other basalt fragments. High Z phases include ilmenite and FeS. Mare basalt chemistry. All basaltic clasts found in Lynch 002 so far contain strongly zoned pyroxenes (e.g. En72Fs22Wo6 to En20Fs59Wo21 in Lithic 4). Fig. 2 shows the compositions of pyroxene from 7 basaltic clasts on the pyroxene quadrilateral. Lithic 5 is the most magnesian and has a more limited range of Fe than the other clasts. Olivine in Lithic 12 is Mg-rich (Fo82-86), but data are lacking for the Fe-rich rims. Lunar basalts are classified by bulk TiO2 abundance. We can classify the basalts found in Lynch 002 by comparing the molar Fe/(Mg+Fe) versus molar Ti/(Ti+Cr) of their pyroxenes with similar data from Apollo basalts, after [3-5]. The results are shown on Fig. 3. All of the basaltic clasts identified so far in Lynch 002 plot in the low-Ti field or between the lowTi and very low Ti (VLT) fields.

Hrz, F.; Borg, J.; Bradley, J.P.; Bridges, John; Brownlee, D.E.; Burchell, M.J.; Cole, M.J.; Dai, Z.R.; Djouadi, Z.; Floss, C.; Franchi, I.A.; Graham, G.A.; Green, S.F.; Heck, P.; Hoppe, P.; Kearsley, A.T.; Leitner, J.; Leroux, H.; Teslich, N.; Marhas, K.K.; Schwandt, C.S.; See, T.H.; Stadermann, F.J.; Stephan, T.; Troadec, D.; Tsou, P.; Zolensky, M.E. and Stardust Cratering Team, The (2006). Microcraters in aluminum foils exposed by Stardust. In: 37th Lunar and Planetary Science Conference, 13-17 March 2006, Houston, Texas, USA.

Borg, J.; Hrz, F.; Bridges, J. C.; Burchell, M. J.; Djouadi, Z.; Floss, C.; Graham, G. A.; Green, S. F.; Heck, P. R.; Hoppe, P.; Huth, J.; Kearsley, A.; Leroux, H.; Marhas, K.; Stadermann, F. J. and Teslich, N. (2007). SEM-EDS analyses of small craters in stardust aluminium foils: implications for the Wild-2 dust distribution. In: 38th Lunar and Planetary Science Conference, 12-16 March 2007, League City, Texas, USA.