Transport Characteristics of a Hierarchical Near-Surface Layer of the Nucleus of Comet 67P/Churyumov–Gerasimenko

Reshetnik, V. N.; Skorov, Yu. V.; Bentley, Mark; Rezac, Ladislav; Hartogh, P.; Blum, Jürgen

doi:10.1134/s0038094622020071

Cited by 7 publications

(5 citation statements)

References 49 publications

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“…Linking these results with those obtained earlier (Skorov et al 2022 ;Reshetnik et al 2022 ), we can conclude that the proposed models satisfactorily describe Knudsen diffusion for the limiting cases of small (up to tens of microns) and very large (on the order of a millimetre) aggregates consisting of micron-and submicronsized monomers. The range of average sizes remains unexplored since both proposed modelling methods do not work well in this case e v aluation of structural characteristics is difficult.…”

Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...supporting

confidence: 81%

“…Earlier we considered free molecular diffusion of gas in porous layers having a hierarchical structure, carrying out the simulation of each elementary scattering of test particle within the particulate medium (Skorov et al 2022 ;Reshetnik et al 2022 ). Such layers were created from relatively small clusters of the BAM2 type (i.e.…”

Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...mentioning

confidence: 99%

“…For the layers under consideration, we use the packings created earlier for homogeneous monodisperse layers of different porosity (Skorov et al 2021 ;Reshetnyk et al 2021 ). From the analysis of previous model layers of aggre gates (Skoro v et al 2022 ;Reshetnik et al 2022 ), we know that the description of hierarchical layers using layers from pseudo-monomers is very successful and completely adequate for our goals. We have shown that the transport characteristics of hierarchical layers built with careful control of layer connectivity (such layers we call 'layers with control o v er contacts') differ only slightly from analogues calculations for layers from pseudo-monomers (for which there is no 'control o v er contacts' between aggregates).…”

Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...mentioning

confidence: 99%

“…The test particle method that we used abo v e to calculate the MFP can be applied directly to obtain a quantitative estimate of the photon path in various types of layers studied herein and in Skorov et al ( 2021Skorov et al ( , 2022, and therefore obtain formulas for the corresponding radiati ve thermal conducti vity. Note that when a ray tracing method or diffusion approach is used, the limits of geometrical optics must be satisfied: a size parameter S go defined as a ratio of grain size to the wavelength of the radiation should be 1.…”

Section: R a D I A T I V E H E A T C O N D U C T I V I T Y E S T I M ...mentioning

confidence: 99%

“…The relation obtained allows using ModelB for the case of very large aggregates, taking into account the radiative heat conduction. To solve a non-linear algebraic system, the same method is used as in Skorov et al ( 2022 ).…”

Section: Data Ava I L a B I L I T Ymentioning

confidence: 99%

See 4 more Smart Citations

Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties

Skorov

Markkanen

Reshetnyk

et al. 2023

Monthly Notices of the Royal Astronomical Society

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The standard approach to obtaining knowledge about the properties of the surface layer of a comet from observations of gas production consists of two stages. First, various thermophysical models are used to calculate gas production for a few sets of parameters. Second, a comparison of observations and theoretical predictions is performed. This approach is complicated because the values of many model characteristics are known only approximately. Therefore, it is necessary to investigate the sensitivity of the simulated outgassing to variations in the properties of the surface layer. This problem was recently considered by us for aggregates up to tens of microns in size. For millimetre-size aggregates, a qualitative extension of the method used to model the structural characteristics of the layer is required. It is also necessary to study the role of radiative thermal conductivity, which may play an important role for such large particles. We investigated layers constructed from large aggregates and having various thicknesses and porosity and evaluated the effective sublimation of water ice at different heliocentric distances. For radiative conductivity, approximate commonly used models and the complicated model based on the dense-medium radiative transfer theory were compared. It was shown that for millimetre-size aggregates careful consideration of the radiative thermal conductivity is required since this mechanism of energy transfer may change the resulting gas productivity by several times. We demonstrate that our model is more realistic for an evolved comet than simple models parameterizing the properties of the cometary surface layer, yet maintains comparable computational complexity.

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Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...supporting

confidence: 81%

Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...mentioning

confidence: 99%

Section: S T Ru C T U R a L C H A R Ac T E R I S T I C S O F T H E L ...mentioning

confidence: 99%

Section: R a D I A T I V E H E A T C O N D U C T I V I T Y E S T I M ...mentioning

confidence: 99%

Section: Data Ava I L a B I L I T Ymentioning

confidence: 99%

See 3 more Smart Citations

Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties

Skorov

Markkanen

Reshetnyk

et al. 2023

Monthly Notices of the Royal Astronomical Society

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Transmission probability of gas molecules through porous layers at Knudsen diffusion

Macher,

Skorov,

Kargl

et al. 2023

J Eng Math

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Gas flow through layers of porous materials plays a crucial role in technical applications, geology, petrochemistry, and space sciences (e.g., fuel cells, catalysis, shale gas production, and outgassing of volatiles from comets). In many applications the Knudsen regime is predominant, where the pore size is small compared to the mean free path between intermolecular collisions. In this context common parameters to describe the gas percolation through layers of porous media are the probability of gas molecule transmission and the Knudsen diffusion coefficient of the medium. We show how probabilistic considerations on layer partitions lead to the analytical description of the permeability of a porous medium to gas flow as a function of layer thickness. The derivations are made on the preconditions that the molecule reflection at pore surfaces is diffuse and that the pore structure is homogenous on a scale much larger than the pore size. By applying a bi-hemispherical Maxwell distribution, relations between the layer transmission probability, the half-transmission thickness, and the Knudsen diffusion coefficient are obtained. For packings of spheres, expressions of these parameters in terms of porosity and grain size are derived and compared with former standard models. A verification of the derived equations is given by means of numerical simulations, also providing evidence that our analytical model for sphere packing is more accurate than the former classical models.

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Dynamics and potential origins of decimeter-sized particles around comet 67P/Churyumov-Gerasimenko

Pfeifer,

Agarwal,

Marschall

et al. 2024

A&A

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One of the primary goals of the European Space Agency's Rosetta mission to comet 67P/Churyumov-Gerasimenko was to investigate the mechanisms responsible for cometary activity. Our aim is to learn more about the ejection process of large refractory material by studying the dynamics of decimeter-sized dust particles in the coma of 67P and estimating their potential source regions. We algorithmically tracked thousands of individual particles through four OSIRIS/NAC image sequences of 67P's near-nucleus coma. We then traced concentrated particle groups back to the nucleus surface, and estimated their potential source regions, size distributions, and projected dynamical parameters. Finally, we compared the observed activity to dust coma simulations. We traced back 409 decimeter-sized particles to four suspected source regions. The regions strongly overlap and are mostly confined to the Khonsu-Atum-Anubis area. The activity may be linked to rugged terrain, and the erosion of fine dust and the ejection of large boulders may be mutually exclusive. Power-law indices fitted to the particle size--frequency distributions range from $3.4 0.3$ to $3.8 0.4$. Gas drag fits to the radial particle accelerations provide an estimate for the local gas production rates ( $Q_ g Our findings strongly suggest that the observed ejection of decimeter-sized particles cannot be explained by water ice sublimation and favorable illumination conditions alone. Instead, the local structures and compositions of the source regions likely play a major role. In line with current ejection models of decimeter-sized particles, we deem an overabundance of CO2 ice and its sublimation to be the most probable driver. In addition, because of the significant initial velocities, we suspect the ejection events to be considerably more energetic than gradual liftoffs.

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Transport Characteristics of a Hierarchical Near-Surface Layer of the Nucleus of Comet 67P/Churyumov–Gerasimenko

Cited by 7 publications

References 49 publications

Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties

Cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties

Transmission probability of gas molecules through porous layers at Knudsen diffusion

Dynamics and potential origins of decimeter-sized particles around comet 67P/Churyumov-Gerasimenko

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