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The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley. Such matter is generally thought to have originated in the interstellar medium, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization. Many gaseous organic molecules, however, have been observed; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.

Abstract: Minerals on earth whose crystalline order has been reduced by radioactive decay of contained atoms are termed “metamict.” They are rare and few because in most crystalline solids, atoms and vacancies are relatively mobile at terrestrial temperatures, and radiation damage tends to be self-annealing. This is not the case in the extreme cold of deep space. Below roughly 100 K, reduced vacancy mobility allows cosmic ray and solar wind induced lattice defects to endure and accumulate for eons, reaching energy densities of up to MJ kg−1 in some materials. We examine the possible effects of the release of energy stored in cold deep-space materials when solid-state defects recombine upon warming due to impacts, gravitational infall, or perihelion. Dimensional analysis suggests energetic defect recombination in radiation-damaged “xenomict” solids in comets, and planetesimals may, in some circumstances, raise internal temperatures enough to melt ice and volatilize frozen gases. We speculate that this may account for some cometary outbursts and Deep Impact experiment results. Calorimetric experiments on appropriately irradiated natural and synthetic materials are needed to further quantify these mechanisms.

Unisized 1.6‐µm polystyrene microspheres coated with PEDOT (polyethylene‐dioxythiophene) were accelerated to speeds of 6–16 km/s and shot onto a silver target. Either positive or negative ions, both instantaneously formed by the impact process, have been analyzed by time‐of‐flight mass spectrometry (TOF). Apparently, the processes that control the formation of ions of either polarity depend on the impact velocity. Comparing the results with those of secondary ion mass spectrometry with primary ion energy in both the elastic and the inelastic (252Cf‐MS) energy loss regimes, some reaction mechanisms of the polymer ions for different energy densities could be elucidated. Some aspects of ion formation are also related to those found in pulsed laser ion generation from these microspheres. This investigation was performed in order to further improve the method of analyzing the organic fraction of interstellar, interplanetary, and cometary dust particles impinging on the targets of the ‘CIDA’ time‐of‐flight (TOF) mass spectrometers on‐board the NASA comet missions ‘STARDUST’ and ‘CONTOUR’. Copyright © 2001 John Wiley & Sons, Ltd.

Unisized 1.6-µm polystyrene microspheres coated with PEDOT (polyethylene-dioxythiophene) were accelerated to speeds of 6–16 km/s and shot onto a silver target. Either positive or negative ions, both instantaneously formed by the impact process, have been analyzed by time-of-flight mass spectrometry (TOF). Apparently, the processes that control the formation of ions of either polarity depend on the impact velocity. Comparing the results with those of secondary ion mass spectrometry with primary ion energy in both the elastic and the inelastic (²⁵²Cf-MS) energy loss regimes, some reaction mechanisms of the polymer ions for different energy densities could be elucidated. Some aspects of ion formation are also related to those found in pulsed laser ion generation from these microspheres. This investigation was performed in order to further improve the method of analyzing the organic fraction of interstellar, interplanetary, and cometary dust particles impinging on the targets of the ‘CIDA’ time-of-flight (TOF) mass spectrometers on-board the NASA comet missions ‘STARDUST’ and ‘CONTOUR’. Copyright © 2001 John Wiley & Sons, Ltd.

In 1997, the COmet Nucleus TOUR (CONTOUR) was selected byNASA for a new start as part of the Discovery line. In this paper, we review the status of the mission, the mission timeline and the instruments to be flown. Detail is given of the science goals and how they are to be accomplished.

The chemical composition of the solid grains from comet Halley can be inferred from impact-ionization time-of-flight mass spectrometry. Halley's dust in the vicinity of the VEGA-1 spacecraft is a mixture of a refractory organic component and unequilibrated silicates, but detailed chemical information on individual particles is difficult to extract because of the complexity of the impact-ionization process.

The Galileo Dust Detector is intended to provide direct observations of dust grains with masses between 10-19 and 10-9 kg in interplanetary space and in the Jovian system, to investigate their physical and dynamical properties as functions of the distances to the Sun, to Jupiter and to its satellites, to study its interaction with the Galilean satellites and the Jovian magnetosphere. Surface phenomena of the satellites (like albedo variations), which might be effects of meteoroid impacts will be compared with the dust environment. Electric charges of particulate matter in the magnetosphere and its consequences will be studied; e.g., the effects of the magnetic field on the trajectories of dust particles and fragmentation of particles due to electrostatic disruption. The investigation is performed with an instrument that measures the mass, speed, flight direction and electric charge of individual dust particles. It is a multicoincidence detector with a mass sensitivity 106 times higher than that of previous in-situ experiments which measured dust in the outer solar system. The instrument weighs 4.2 kg, consumes 2.4 W, and has a normal data transmission rate of 24 bits s-1 in nominal spacecraft tracking mode. On December 29, 1989 the instrument was switched-on. After the instrument had been configured to flight conditions cruise science data collection started immediately. In the period to May 18, 1990 at least 168 dust impacts have been recorded. For 81 of these dust grains masses and impact speeds have been determined. First flux values are given.

During encounters with comet Halley, the experiment PICCA onboard GIOTTO measured the gas phase organic ion composition of the coma and the experiment PUMA onboard VEGA-1 measured the dust composition. Joining both results, we obtain a consistent picture of the parent organic matter from which dust and gas is produced. One recognizes a complex unsaturated polycondensate, which splits during coma-formation into the more refractory C=C,C-N-containing dust part, and the more volatile C=C,C-O-containing gas part. The responsible exothermal chemical reactions, which are triggered by the sunlight, may play a major role in the dynamics of coma formation.

In a previous article describing the cloud of attogram dust particles surrounding Comet Halley, the present authors noted a sharp break in the curve of signal amplitude (related to particle size) versus distance to the comet. Arguments were given which supported the explanation that the break was instrumental rather than due to a physical structure in the coma. At that time no conclusive evidence was available. In the meantime a paper by other authors has appeared which concluded that this “glitch” was due to a physical process in the coma and presented a theory to explain it. Recently the present authors have found very strong evidence in the telemetry data that the glitch was instrumental. However this finding does not change the conclusion by all the authors referenced here that the signals at large distances from the comet were due to attogram dust particles.

From our analysis of composition and structure of cometary grains some thermodynamic aspects concerning biogenesis arose. Assuming any kind of hypercyclic organization as first step having come into existence spontaneously, some prerequisites are necessary from thermodynamics of irreversible processes, e.g.: large concentration gradients of certain substances and high affinities of their reactions catalyzed at surfaces, small semipermeable compartments due to the related diffusion coefficients, large reservoirs of substrates and for products. Neither an isothermal dilute-soup nor a cometary pond scenario can probably meet these requirements. However, cometary grains as found in p/Halley added to an aqueous solution of nutrient organics on earth may fulfill the requirements of chemical thermodynamics (two types of matter on very different chemical potential at the same place and time) to start molecular self-organization. As the probability of partwise survival of cometary matter during atmospheric entry is regarded not to be low, if sufficiently deep lakes or an ocean collect the cometary pieces, this combined space- and earth-borne scenario could provide a model of origin of life which may overcome problems of previous ones.