‘Kosi’ comet simulation experiment at DFVLR: Sample preparation and the evolution of the 18O/16O and the D/H ratio in the icy component

doi:10.1016/0273-1177(89)90250-0

Advances in Space Research

Volume 9, Issue 3, 1989, Pages 123-125

https://doi.org/10.1016/0273-1177(89)90250-0 Get rights and content

Abstract

Based on the results of the observation campaign of comet Halley, ice-mineral mixtures were produced with a mean density of 300 to 500 kg/m³ and an albedo between about 0.05 and 0.2. The samples were prepared by spraying different water-mineral mixtures into liquid nitrogen. As a propellant we used nitrogen or carbon dioxide. with carbon dioxide we obtained ices with two components (H₂O and CO₂). Sample preparation methods from the gas phase are under development. During the freezing a slight enrichment in ¹⁸O and deuterium was produced. After the iradiation with an artificial sun, the uppermost layers of the sample showed an important enrichment of heavy isotopes. This was also observed in the lowest layers whereas the intermediate layer showed no isotope fractionation.

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Cited by (5)

Towards a model of cometary nuclei for engineering studies for future space missions to comets
1996, Planetary and Space Science
A brief review is given of the present state of knowledge on comets. Existing comet models are critically analysed in view of these observational facts. This analysis leads to the conclusion that the most promising model approach is one where the comet nucleus is considered as a porous medium containing an intimate mixture of dust particles and different ices. Compact nuclei can be treated as limiting cases. An outline of a pseudo-tridimensional model based on this approach is given. The hypothesis is made that comets initially contain a mixture of amorphous water ice, solid carbon monoxide and silicate dust. As examples, local production rates of CO and integrated production rates of H₂O and CO for comets P/Schwassmann-Wachmann 1 and P/Schwassmann-Wachmann 3 are calculated, making the extreme assumption that all the devolatilized dust remains on the surface. The depletion of CO in the near surface layers is determined after ten revolutions. Under the assumptions that all the dust remains on the surface or that all the dust is lifted off, thermal profiles at the equator of a nucleus on the orbit of comet P/Wirtanen with the rotation axis perpendicular to the orbital plane are determined when the surface temperature is maximum or minimum. The evolution of the maximum and minimum surface temperature is computed over ten orbital periods for two values of the bulk thermal conductivity of the dust coverage. For the same comet, the relative H₂O and CO content as a function of depth are calculated for a dust covered and a non-dust covered nucleus. Improvements of the present day model are suggested and a strategy is proposed for adapting this model for complex and thus more realistic situations.
Modeling of the thermal behavior and of the chemical differentiation of cometary nuclei
1991, Icarus
Taking into account the low values of average density reported for Comet P/Halley, a model of a porous comet nucleus has been developed. The model includes heat conduction through the solid matrix and heat and mass transfers due to the vapor phase circulating in the pore system. Sublimation and recondensation of volatile species within the nucleus as well as water ice crystallization are represented according to experimental results on the evolution of ice mixtures with time and temperature. The model is based on the resolution of two symmetric diffusion equations through the whole nucleus, one describing the transport of matter and the other the transport of heat. These equations are linked by the source term. The sensible heat term due to gas advection is also integrated into the heat diffusion equation. The calculations are performed for comets on the orbits of P/Halley and P/Churyumov-Gerasimenko. Different nucleus compositions with ice mixtures containing H₂O and CO or CO₂ are investigated. The consequences of the amorphous to crystalline phase transition of water ice on the thermal profiles and on the evolution of the composition of the nucleus are studied. Results are presented on the evolution of the stratigraphy of the nucleus and of the production rates of CO, CO₂, and H₂O as a function of the heliocentric distance. Several phenomena are evidenced such as the depletion of volatiles in the subsurface layers and their enrichment in deeper layers. The important role of CO and CO₂ in controlling the propagation of the phase transition is emphasized. The relation between the composition of the nucleus and gas production rates is discussed.
Thermal history models for KOSI sublimation experiments
1990, Icarus
Temperatures recorded during three KOSI (Kometensimulation) sublimation experiments with porous ice/dust samples strongly suggest that heat transport by vapor flow into the interior of the samples was important. We propose a model of coupled heat and mass transfer that is capable of explaining the measured thermal histories of the samples. It is suggested that similar heat transfer mechanisms may operate in porous ice layer on cometary nuclei and on other icy bodies in the solar system. For the first two experiments with samples consisting of a water-ice/dust mixture in the mass ratio $101$ and having a porosity of about 0.4, we calculated that the vapor transferred about 60% of the insolation through the interior of the samples to a constant-temperature (≈100°K) backplate. The thermal diffusivities of the ice/dust matrixes of these samples were estimated to be (7 ± 4) × 10⁻⁸ and (2 ± 1) × 10⁻⁸ m² sec⁻¹, respectively. The presence of 14% by weight CO₂ in the sample of the third experiment acted as a strong heat sink which slowed the heating of the sample considerably. This sample developed a three-layer structure of, from top to bottom, a dust mantle, a water-ice/dust layer, and water-ice/CO₂-ice/dust layer. The thermal diffusivity of the ice/dust matrix was found to be (6 ± 2) × 10⁻⁸ m² sec⁻¹. The upward flow of CO₂ vapor from the deep layer reduced the rate of downward energy transfer via the water vapor to 37% of the insolation. In the CO₂-enriched layer the rate of vapor heat transfer was 50% of the heat flux incident on the CO₂-ice sublimation front. The dust mantle that formed on all samples is calculated to have caused a temperature rise of the ice of about 15°K above the free sublimation temperature.
Cometary deuterium
1999, Space Science Reviews
Comets - II. Models, evolution, origin and outlook
1993, The Astronomy and Astrophysics Review

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‘Kosi’ comet simulation experiment at DFVLR: Sample preparation and the evolution of the 18O/16O and the D/H ratio in the icy component

Abstract

Mases and Densities of Comet Halley and Kopff, Comet Nucleus Sample Return

ESA SP-249

Is the Nucleus of Comet Halley a low Density Body?

Nature

‘Kosi’ comet simulation experiment at DFVLR: Sample preparation and the evolution of the ^18O/¹⁶O and the D/H ratio in the icy component