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After a brief review of the instrument development and materials selection for collecting cometary dust in the vicinity of comet 67/P Churyumov–Gerasimenko we focus on laboratory verification for the capability of metal black targets to decelerate and capture dust particles (velocities in the order of 100 m/s; sizes of some 10 μm). The results indicate that particles between 10 and 100 μm size can be collected with high probability. Two basic mechanisms of energy dissipation upon impact could be identified: By internal friction within a highly structured dust and within the black’s nanostructure. In addition to the actual ROSETTA mission the data presented here might have a more general relevance for future, similar in-situ investigations. [ABSTRACT FROM AUTHOR]

The instrument COSIMA (COmetary Secondary Ion Mass Analyzer) onboard of the European Space Agency mission Rosetta collected and analyzed dust particles in the neighborhood of comet 67P/Churyumov‐Gerasimenko. The chemical composition of the particle surfaces was characterized by time‐of‐flight secondary ion mass spectrometry. A set of 2213 spectra has been selected, and relative abundances for CH‐containing positive ions as well as positive elemental ions define a set of multivariate data with nine variables. Evaluation by complementary chemometric techniques shows different compositions of sample groups collected during two periods of the mission. The first period was August to November 2014 (far from the Sun); the second period was January 2015 to February 2016 (nearer to the Sun). The applied data evaluation methods consider the compositional nature of the mass spectral data and comprise robust principal component analysis as well as classification with discriminant partial least squares regression, k‐nearest neighbor search, and random forest decision trees. The results indicate a high importance of the relative abundances of the secondary ions C+ and Fe+ for the group separation and demonstrate an enhanced content of carbon‐containing substances in samples collected in the period with smaller distances to the Sun. Extraterrestrial dust particles from the neighborhood of comet 67P/Churyumov‐Gerasimenko have been collected by the instrument COSIMA onboard of the European Space Agency mission Rosetta. The composition of the particles was characterized by time‐of‐flight secondary ion mass spectrometry giving evidence of minerals and macromolecular organic substances. A specific multivariate evaluation of the mass spectral data by chemometric methods indicates an enhanced content of carbon‐containing substances in samples collected in a period with smaller distances to the Sun. [ABSTRACT FROM AUTHOR]

Zusammenfassung Der mit dem Instrument COSIMA gesammelte Staub des Kometen 67P/Tschurjumow‐Gerassimenko ist porös und besteht aus 10 bis 40 µm großen Agglomeraten. Van‐der‐Waals‐Kräfte halten diese zusammen. Die Teilchen bestehen zu einem Drittel aus Kohlenstoff. Vergleichbare hochporöse Staubteilchen haben wir bisher auf der Erde nicht gefunden, wenn auch eine Reihe von Meteoriten und Mikrometeoriten oder in der Atmosphäre aufgesammelte interplanetare Staubteilchen einzelne Eigenschaften der mit Rosetta gemachten Beobachtungen gut widerspiegeln. Zwei Jahre lang begleitete die Raumsonde Rosetta den Kometen Tschurjumow‐Gerassimenko. Währenddessen untersuchte das an Bord befindliche Instrument COSIMA von ihm abströmende Staubteilchen und ermittelte deren mechanische, elektrische und optische Eigenschaften sowie die chemische Zusammensetzung. [ABSTRACT FROM AUTHOR]

Abstract: The instrument Cometary Secondary Ion Mass Analyzer (COSIMA) on board of the European Space Agency mission Rosetta to the comet 67P/Churyumov‐Gerasimenko is a secondary ion mass spectrometer with a time‐of‐flight mass analyzer. It collected near the comet several thousand particles, imaged them, and analyzed the elemental and chemical compositions of their surfaces. In this study, variables have been generated from the spectral data covering the mass ranges of potential C‐, H‐, N‐, and O‐containing ions. The variable importance in binary discriminations between spectra measured on cometary particles and those measured on the target background has been estimated by the univariate t test and the multivariate methods discriminant partial least squares, random forest, and a robust method based on the log ratios of all variable pairs. The results confirm the presence of organic substances in cometary matter—probably a complex macromolecular mixture. [ABSTRACT FROM AUTHOR]

Soon after the arrival of the ROSETTA spacecraft at Comet 67/P Churyumov-Gerasimenko the onboard instrument COSIMA (“Cometary Secondary Ion Mass Analyzer”) collected a large number of cometary dust particles on targets from gold black of thickness between 10 and 30 μm. Inspection by its camera subsystem revealed that many of them consist of smaller units of typically some tens of micrometers in size. The collection process left the smaller dust particles in an essentially unaltered state whereas most particles larger than about 100 μm got fragmented into smaller pieces. Using the observed fragment size distributions, the present paper includes a first assessment of the strength for those dust particles that were disrupted upon impact. [ABSTRACT FROM AUTHOR]

The calcium-aluminum-rich inclusions ( CAIs) found in chondritic meteorites are probably the oldest solar system solids, dating back to 4567.30 ± 0.16 million years ago. They are thought to have formed in the protosolar nebula within a few astronomical units of the Sun, and at a temperature of around 1300 K. The Stardust mission found evidence of CAI-like material in samples recovered from comet Wild 2. The appearance of CAIs in comets, which are thought to be formed at lower temperatures and larger distances from the Sun, is only explicable if some mechanism allows the efficient transfer of such objects from the inner solar nebula to the outer solar nebula. Such mechanisms have been proposed such as an X-wind or turbulence. In this work, particles collected from within the coma of comet 67P/Churyumov-Gerasimenko are examined for compositional evidence of the presence of CAIs. COSIMA (the Cometary Secondary Ion Mass Analyzer) uses secondary ion mass spectrometry to analyze the composition of cometary dust captured on metal targets. While CAIs can have a radius of centimeters, they are more typically a few hundred microns in size, and can be smaller than 1 μm, so it is conceivable that particles visible on COSIMA targets (ranging in size from about 10 μm to hundreds of microns) could contain CAIs. Using a peak fitting technique, the composition of a set of 13 particles was studied, looking for material rich in both calcium and aluminum. One such particle was found. [ABSTRACT FROM AUTHOR]

Abstract: The coma of Comet 103P/Hartley 2 has a significant population of large particles observed as point sources in images taken by the Deep Impact spacecraft. We measure their spatial and flux distributions, and attempt to constrain their composition. The flux distribution of these particles implies a very steep size distribution with power-law slopes ranging from −6.6 to −4.7. The radii of the particles extend up to 20cm, and perhaps up to 2m, but their exact sizes depend on their unknown light scattering properties. We consider two cases: bright icy material, and dark dusty material. The icy case better describes the particles if water sublimation from the particles causes a significant rocket force, which we propose as the best method to account for the observed spatial distribution. Solar radiation is a plausible alternative, but only if the particles are very low density aggregates. If we treat the particles as mini-nuclei, we estimate they account for <16–80% of the comet’s total water production rate (within 20.6 km). Dark dusty particles, however, are not favored based on mass arguments. The water production rate from bright icy particles is constrained with an upper limit of 0.1–0.5% of the total water production rate of the comet. If indeed icy with a high albedo, these particles do not appear to account for the comet’s large water production rate. [Copyright &y& Elsevier]

Abstract: Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33km in length. Surface features are primarily small mounds <40m across, irregularly-shaped smooth areas on the two lobes, and a smooth but variegated region forming a “waist” between the two lobes. Assuming parts of the comet body approach the shape of an equipotential surface, the mean density of Hartley 2 is modeled to be 200–400kgm−3. Such a mean density suggests mass loss per orbit of >1%. The shape may be the evolutionary product of insolation, sublimation, and temporary deposition of materials controlled by the object’s complex rotation. [Copyright &y& Elsevier]

Abstract: Random projection (RP) is a simple and fast linear method for dimensionality reduction of high-dimensional multivariate data, independent from the data. The method is briefly described and a new memory-saving algorithm is presented for the generation of random projection vectors. Application of RP to data from scanning experiments with a time-of-flight secondary ion mass spectrometer (TOF-SIMS) showed that data reduced by RP have a satisfying discriminant property for separating target material and minerals without using any knowledge about the composition of the sample. A selection method – based on low dimensional RP data – is described and successfully tested for automatic recognition of characteristic, diverse locations of a sample surface. RP is demonstrated as an unbiased, powerful method, especially for large data sets, severe hardware restrictions (such as in space experiments) or the need for fast data evaluation of hyperspectral data. [Copyright &y& Elsevier]

The article focuses on cometary research and the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) unmanned space mission. It states EPOXI flew past comet Hartley 2 on November 4, 2010 and took photographs and spectrographic measurements. It comments that Hartley 2 has a small and active nucleus that is outgassing carbon dioxide which drags particles of ice out of the nucleus. It talks about the comet's surface geology and the average geometric albedo and on differences between Hartley 2 and the comet Tempel 1.

Abstract: We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441–446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230–238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253–263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136–2160; 1999a. Astron. J. 118, 1101–1119; 1999b. Astrophys. J. 526, 465–470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255–1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220–229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670–1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193–204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects. [Copyright &y& Elsevier]

Abstract: We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441–446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230–238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253–263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136–2160; 1999a. Astron. J. 118, 1101–1119; 1999b. Astrophys. J. 526, 465–470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255–1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220–229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670–1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193–204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects. [Copyright &y& Elsevier]

In 1998, Comet 9P/Tempel 1 was chosen as the target of the Deep Impact mission (A’Hearn, M. F., Belton, M. J. S., and Delamere, A., Space Sci. Rev., 2005) even though very little was known about its physical properties. Efforts were immediately begun to improve this situation by the Deep Impact Science Team leading to the founding of a worldwide observing campaign (Meech et al., Space Sci. Rev., 2005a). This campaign has already produced a great deal of information on the global properties of the comet’s nucleus (summarized in Table I) that is vital to the planning and the assessment of the chances of success at the impact and encounter. Since the mission was begun the successful encounters of the Deep Space 1 spacecraft at Comet 19P/Borrelly and the Stardust spacecraft at Comet 81P/Wild 2 have occurred yielding new information on the state of the nuclei of these two comets. This information, together with earlier results on the nucleus of comet 1P/Halley from the European Space Agency’s Giotto, the Soviet Vega mission, and various ground-based observational and theoretical studies, is used as a basis for conjectures on the morphological, geological, mechanical, and compositional properties of the surface and subsurface that Deep Impact may find at 9P/Tempel 1. We adopt the following working values ( circa December 2004) for the nucleus parameters of prime importance to Deep Impact as follows: mean effective radius = 3.25± 0.2 km, shape – irregular triaxial ellipsoid with a/ b = 3.2± 0.4 and overall dimensions of ∼14.4 × 4.4 × 4.4 km, principal axis rotation with period = 41.85± 0.1 hr, pole directions (RA, Dec, J2000) = 46± 10, 73± 10 deg (Pole 1) or 287± 14, 16.5± 10 deg (Pole 2) (the two poles are photometrically, but not geometrically, equivalent), Kron-Cousins (V-R) color = 0.56± 0.02, V-band geometric albedo = 0.04± 0.01, R-band geometric albedo = 0.05± 0.01, R-band H(1,1,0) = 14.441± 0.067, and mass ∼7×1013 kg assuming a bulk density of 500 kg m−3. As these are working values, {i.e.}, based on preliminary analyses, it is expected that adjustments to their values may be made before encounter as improved estimates become available through further analysis of the large database being made available by the Deep Impact observing campaign. Given the parameters listed above the impact will occur in an environment where the local gravity is estimated at 0.027–0.04 cm s−2 and the escape velocity between 1.4 and 2 m s−1. For both of the rotation poles found here, the Deep Impact spacecraft on approach to encounter will find the rotation axis close to the plane of the sky (aspect angles 82.2 and 69.7 deg. for pole 1 and 2, respectively). However, until the rotation period estimate is substantially improved, it will remain uncertain whether the impactor will collide with the broadside or the ends of the nucleus. [ABSTRACT FROM AUTHOR]

Images taken by the Stardust mission during its flyby of 81P/Wild 2 show the comet to be a 5-kilometer oblate body covered with remarkable topographic features, including unusual circular features that appear to be impact craters. The presence of high-angle slopes shows that the surface is cohesive and self-supporting. The comet does not appear to be a rubble pile, and its rounded shape is not directly consistent with the comet being a fragment of a larger body. The surface is active and yet it retains ancient terrain. Wild 2 appears to be in the early stages of its degradation phase as a small volatile-rich body in the inner solar system. [ABSTRACT FROM AUTHOR]

Comets are composed of dust and frozen gases. The ices are mixed with the refractory material either as an icy conglomerate, or as an aggregate of pre-solar grains (grains that existed prior to the formation of the Solar System), mantled by an ice layer. The presence of water-ice grains in periodic comets is now well established. Modelling of infrared spectra obtained about ten kilometres from the nucleus of comet Hartley 2 suggests that larger dust particles are being physically decoupled from fine-grained water-ice particles that may be aggregates, which supports the icy-conglomerate model. It is known that comets build up crusts of dust that are subsequently shed as they approach perihelion. Micrometre-sized interplanetary dust particles collected in the Earth's stratosphere and certain micrometeorites are assumed to be of cometary origin. Here we report that grains collected from the Jupiter-family comet 67P/Churyumov-Gerasimenko come from a dusty crust that quenches the material outflow activity at the comet surface. The larger grains (exceeding 50 micrometres across) are fluffy (with porosity over 50 per cent), and many shattered when collected on the target plate, suggesting that they are agglomerates of entities in the size range of interplanetary dust particles. Their surfaces are generally rich in sodium, which explains the high sodium abundance in cometary meteoroids. The particles collected to date therefore probably represent parent material of interplanetary dust particles. This argues against comet dust being composed of a silicate core mantled by organic refractory material and then by a mixture of water-dominated ices. At its previous recurrence (orbital period 6.5 years), the comet's dust production doubled when it was between 2.7 and 2.5 astronomical units from the Sun, indicating that this was when the nucleus shed its mantle. Once the mantle is shed, unprocessed material starts to supply the developing coma, radically changing its dust component, which then also contains icy grains, as detected during encounters with other comets closer to the Sun. [ABSTRACT FROM AUTHOR]

We describe recent results on the CO/CO2/H2O composition of comets together with a survey of older literature (primarily for CO/H2O) and compare these with models of the protoplanetary disk. Even with the currently small sample, there is a wide dispersion in abundance ratios and little if any systematic difference between Jupiter-family comets (JFCs) and long-period and Halley-type comets (LPCs and HTCs). We argue that the cometary observations require reactions on grain surfaces to convert CO to CO2 and also require formation of all types of comets in largely, but not entirely, overlapping regions, probably between the CO and CO2 snow lines. Any difference in the regions of formation is in the opposite direction from the classical picture with the JFCs having formed closer to the Sun than the LPCs. In the classical picture, the LPCs formed in the region of the giant planets and the JFCs formed in the Kuiper Belt. However, these data suggest, consistent with suggestions on dynamical grounds, that the JFCs and LPCs formed in largely overlapping regions where the giant planets are today and with JFCs on average forming slightly closer to the Sun than did the LPCs. Presumably at least the JFCs passed through the scattered disk on their way to their present dynamical family. [ABSTRACT FROM AUTHOR]