Origin of cometary extended sources from degradation of refractory organics on grains: polyoxymethylene as formaldehyde parent molecule

The radial distribution of some molecules (CO, H₂CO, HNC, …) observed in the coma of some comets cannot be explained only by a direct sublimation from the nucleus, or by the photolysis of a detected parent compound. Such molecules present a so-called extended source in comae. We show in this paper that extended sources can be explained by refractory organic material slowly releasing gas from grains ejected from the cometary nucleus, due to solar UV photons or heat. The degradation products are produced throughout the coma and therefore are presenting an extended distribution. To model this multiphase chemistry we derive new equations, which are applied to Comet 1P/Halley for the case of the production of formaldehyde from polyoxymethylene (POM), the polymer of formaldehyde (-CH₂-O-)_n. We show that the presence of a few percent of POM on cometary grains (a nominal value of ∼4% in mass of grains is derived from our calculations) is in good agreement with the observed distribution, which so far were not interpreted by the presence of any gaseous parent molecule.     

Sources of cometary radicals and their jets: Gases or grains

The recent discovery of CN and C₂ gas jets in comet Halley has led to basic speculation as to their physical source mechanism. A basic quantitative study of the photosputtering of CHON grains and the spatial evolution of trace gas jets is presented here. Two possible single sources, a parent gas and CHON grains, for both the jet and the background gas, are also investigated. It is shown that a parent trace gas jet will remain focused out to distances as large as 10⁵ km from the nucleus and could provide a source for the observed radical jets. Conversely, photosputtering of small CHON grains by solar UV radiation can provide the source not only for cometary CN and C₂ but also possibly for inner coma C atoms and C⁺ ions. However, constraints on the size and/or morphology of the contributing grains themselves are found. Isotropic speed components comparable to the outflow speed are likely to be added to radicals upon production from either the CHON grain or the parent gas source and will yield a radical jet which becomes more diffuse with increasing distance from the nucleus. However, in neither case will the radical jet completely isotropicize; it will be confined generally to a quadrant as projected on the sky plane. Observational tests which can be made once the large set of in situ and remote observations have been analyzed are suggested to distinguish between the two scenarios.     

Modelling the circumnuclear coma of comets: objectives,methods and recent results

We investigate whether the modelling of the immediate vicinity of an active nucleus—currently unobservable—can, as the modelling of the outer, observable coma, be based on unrealistic simple assumptions such as those of nucleus and dust grains sphericity. We point out the inconsistency of models based on such assumptions, which, to manage compatibility with the observations, have to introduce additional assumptions that conflict with the previous ones, such as the existence of active areas of the nucleus. We argue that, while the outer coma models being phenomenological in nature, can perhaps tolerate such inconsistencies, the circumnuclear coma models must be predictive, having to obviate the lack of observational data, and therefore must exclude implausible and ad hoc assumptions, and advocate only well-understood physical processes and duly validated modelling methods. We describe the first steps of development of a predictive circumnuclear coma model, and present a set of results obtained with parameters fitted to comet P/Wirtanen, the target of the Rosetta mission, but of a quite general significance. Considering, first an inhomogeneous spherical nucleus with spherical dust grains, and then an aspherical homogeneous nucleus with spherical dust grains, we show that, in both cases (1) the surface temperature and initial gas parameters differ considerably from the Hertz–Knudsen values; (2) the near-surface gas and dust flows are not in general vertical, (3) the gas and dust density do not always monotonically decrease outwards, (4) the gas and dust velocity vary strongly from point to point, (5) shock structures are formed, which result in the formation of pseudo-jets of dust grains originating from various points of the surface. No simple method to distinguish between dust structures created by the surface inhomogeneity and by the surface orography is found. We show, for the first time, the deformation of the near-nucleus dust coma during a full rotation of an homogeneous, aspherical nucleus. We also show that identical active regions located at different points of an inhomogeneous spherical nucleus produce very different dust distributions, suggesting that the dust distribution is also strongly deformed during the rotation of such a nucleus. Finally, we consider, for the first time, a spherical homogeneous nucleus emitting aspherical dust grains. We show that, in such a case, the terminal grain velocity depends upon the shape, initial position, and even possibly upon the initial orientation of the grain at the surface, so that there cannot exist a precise relation between terminal velocity and dust grain mass. We conclude that, far from giving an approximate or average representation of the circumnuclear coma, the classical modelling approach yields in this region predictions that are in total conflict with the real behaviour of the gas and dust. As a most dramatic consequence, the use of this classical approach may have obscured completely the significance of the few direct and of the many indirect informations acquired hitherto on the nucleus activity.     

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors

Analysis of the data from Giotto's Dust Impact Detection System experiment (DIDSY) is presented. These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14. First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus. In order to improve the data coverage (and especially for the smallest grains, to approximately 10(-19) kg particle mass), data from the PIA instrument has been combined with DIDSY data. Flux profiles are presented for the various mass channels showing, to a first approximation, a 1/R2 flux dependence, where R is the distance of the detection point from the cometary nucleus, although significant differences are noted. Deviations from this dependence are observed, particularly close to the nucleus. From the flux profiles, mass and geometrical area distributions for the dust grains are derived for the trajectory through the coma. Groundbased CCD imaging of the dust continuum in the inner coma at the time of encounter is also used to derive the area of grains intercepted by Giotto. The results are consistent with the area functions derived by Giotto data and the low albedo of the grains deduced from infrared emission. For the close encounter period (-5 min to +5 min), the cumulative mass distribution function has been investigated, initially in 20 second periods; there is strong evidence from the data for a steepening of the index of the mass distribution for masses greater than 10(-13) kg during passage through dust jets which is not within the error limits of statistical uncertainty. The fluences for dust grains along the entire trajectory is calculated; it is found that extrapolation of the spectrum determined at intermediate masses (cumulative mass index alpha = 0.85) is not able to account for the spacecraft deceleration as observed by the Giotto Radio Science Experiment and by ESOC tracking operations. Data at large masses (>10(-8) kg) recently analysed from the DIDSY data set show clear evidence of a decrease in the mass distribution index at these masses within the coma, and it is shown that such a value of the mass index can provide sufficient mass for consistency with the observed deceleration. The total particulate mass output from the nucleus of comet P/Halley at the time of encounter would be dependent on the maximum mass emitted if this change in slope observed in the coma were also applicable to the emission from the nucleus; this matter is discussed in the text. The flux time profiles have been converted through a simple approach to modeling of the particle trajectories to yield an indication of nucleus surface activity. There is indication of an enhancement in flux at t approximately -29 s corresponding to crossing of the dawn terminator, but the flux detected prior to crossing of the dawn terminator is shown to be higher than predicted by simple modelling. Further enhancements corresponding to jet activity are detected around +190 s and +270 s.     

Coma expansion and photometry of comet Bowell (1980b)

Optical and infrared observations of comet Bowell are presented. The optical observations indicate that the solid grain coma is expanding at only 0.9 ± 0.2 m sec^?1. This is two orders of magnitude slower than the local gas sound speed and may suggest that gas drag is not responsible for stripping the grains from the nucleus. The hypothesis of “electrostatic snap-off” is tentatively advanced to account for the ejection of the grains. Alternatively, the grains may have an unusual size distribution. The extrapolated motion of the grains suggests that the bulk of the coma was formed when the comet was at a heliocentric distance $\text{R ? 10}\text{AU}$. Any water ice in the nucleus would be too cold to give rise to the observed grain coma by equilibrium sublimation at this R. Further evidence against the production of the grain coma by equilibrium sublimation of the nucleus is provided by broadband (J) photometric observations. Almost all of the observed photometric variations of comet Bowell can be ascribed to geometric effects. Simple models indicate that the total grain cross section has been nearly constant since the time of the earliest observations. The present observations, which suggest that water ice sublimation does not control either the optical morphology or the near infrared photometric behavior of comet Bowell, are contrasted with reported high OH production rates. It is concluded that the grain coma may be largely a relic of activity occurring on the nucleus at $\text{R ? 10}\text{AU}$ while the OH may indicate sublimation from the nucleus near perihelion and from coma grains near $\text{R ? 4.6}\text{AU}$.     

Monte-Carlo and multifluid modelling of the circumnuclear dust coma II. Aspherical-homogeneous, and spherical-inhomogeneous nuclei

We use our newly developed Dust Monte-Carlo (DMC) simulation technique [Crifo, J.F., Lukianov, G.A., Rodionov, A.V., Zakharov, V.V., 2005. Icarus 176, 192-219] to study the dynamics of dust grains in the vicinity of some of the benchmark aspherical, homogeneous cometary nuclei and of the benchmark spherical, inhomogeneous nuclei studied by us precedingly. We use the interim unrealistic simplifying assumptions of grain sphericity, negligible nucleus rotation rate, and negligible tidal force, but take accurately into account the nucleus gravitational force, gas coma aerodynamic force, and solar radiation pressure force, and consider the full mass range of ejectable spherical grains. The resulting complicated grain motions are described in detail, as well as the resulting complicated and often counter-intuitive dust coma structure. The results are used to answer several important questions: (1) When computing coma dust distributions, (a) is it acceptable to take into consideration only one or two of the above mentioned forces (as currently done)? (b) to which accuracy must these forces be known, in particular is it acceptable to represent the gravity of an aspherical nucleus by a spherically symmetric gravity? (c) how do the more efficient but less general Dust Multi-Fluid (DMF) computations compare with the DMC results? (2) Are there simple structural relationships between the dust coma of a nucleus at small heliocentric distance rh, and that of the same nucleus at large rh? (3) Are there similarities between the gas coma structures and the associated dust coma structures? (4) Are there dust coma signatures revealing non-ambiguously a spherical nucleus inhomogeneity or an homogeneous nucleus asphericity? (5) What are the implications of the apparently quite general process of grain fall-backs for the evolution of the nucleus surface, and for the survival of a landed probe?     

The distribution of dust in the inner coma of comet IRAS-Araki-Alcock (1983d)

High-resolution images of comet IRAS-Araki-Alcock taken on five separate through its closest approach to the Earth are presented. The images were taken in the red and near-infrared, and so consist primarily of continuum scattering from dust grains. The distribution of dust in the inner coma varied widely from day to day, although the dust was emitted primarily in the sunward direction on all days. The main emission exhibited a lag angle consistent with a nuclear rotational vector that was oriented approximately along the line of sight on May 11.3 1983 UT. A curved filament, extending in the sunward direction, was seen in the deepest images obtained on this day as well, and the azimuthal distribution of dust was strongly of dust was strongly peakeed in the sunward direction. The presence of the curved filament is indicative of dust outflow from an active region, on a mantled nucleus. On all days, the brightness falls off slower than the r⁻ expected for uniform outflow, which is interpreted as resulting from fragmentation of the dust grains as they traveled through the coma. The nuclear region appeared stellar on all days. The seeing-limited spatial resolutions was 19 km on May 11.3, but deconvolution of the images with the instrumental profile enables an upper limit of 17 km to be placed on the diameter of the nucleus.     

Millimeter-wave experiments for cometary space missions

Predicted brightness temperatures for a variety of cometary nucleus models, consisting of homogeneous layers comprised of mixtures of water ice and refractory grains, are presented as functions of wavelength. These illustrative spectra are computed using simple radiative transfer techniques adapted from modeling of terrestrial ice and snow fields. The computed millimeter-wave spectra are sensitive to the values of physically significant nucleus parameters such as crust thickness, the subsurface temperature gradient, and the boundary temperature of the sublimating surface. It appears that millimeter-wave sensing from an interplanetary spacecraft is an effective means for distinguishing between alternate models of the nucleus and for inferring the rough physical state of substrata; modern theories on the nature of the nucleus indicate that sublimation from the substrata provides the gas phase cometary volatiles that are actually observed from ground-based and Earth-orbiting instruments. Antenna beam dilution is a major obstacle for ground-based molecular spectral line radio observations (e.g., water and ammonia) of comets but a modest millimeter-wave radiometer system in the near vicinity of the comet would not be subject to this problem. Such a system can make definitivebservations of several candidate parent molecules in the gas phase and should contribute to the understanding of the physics of the inner coma.     

Models of P/Wirtanen nucleus: active regions versus non-active regions

From the current understanding we know that comet nuclei have heterogeneous compositions and complex structures. It is believed that cometary activity is the result of a combination of physical processes in the nucleus, like sublimation and recondensation of volatile ices, dust grains release, phase transition of water ice, depletion of the most volatile components in the outer layers and interior differentiation.The evolution of the comet depends on the sublimation of ices and the release of different gases and dust grains: the formation of a dust crust, the surface erosion and the development of the coma are related to the gas fluxes escaping from the nucleus. New observations, laboratory experiments and numerical simulations suggest that the gas and dust emissions are locally generated, in the so-called active regions. This localized activity is probably superimposed to the global nucleus activity. The differences between active and inactive regions can be attributed to differences in texture and refractory material content of the different areas.In this paper we present the results of numerical models of cometary nucleus evolution, developed in order to understand which are the processes leading to the formation of active and non-active regions on the cometary surface. The used numerical code solves the equations of heat transport and gas diffusion within a porous nucleus composed of different ices—such as water (the dominant constituent), CO₂, CO- and of dust grains embedded in the ice matrix.By varying the set of physical parameters describing the initial properties of comet P/Wirtanen, the different behaviour of the icy and dusty areas can be followed.Comet P/Wirtanen is the target of the international ROSETTA mission, the cornerstone ESA mission to a cometary nucleus. The successful design of ROSETTA requires some knowledge of comet status and activity: surface temperatures, amount of active and inactive surface areas, gas production rate and dust flux.     

Some constraints on particles in Saturn's spokes

The consequences of taking into account some physical processes previously ignored in the context of Saturn's spokes were studies. Secondary emission, which can ensure large changes of potential following small environment variations, may provide a plausible mechanism for triggering spoke formation. Taking into account the grains' centrifugal disruption due to their spin, should modify the constraints on size previously derived on the basis of electrostatic disruption alone. Taking into account the dielectric polarization when calculating the electrostatic forces on grains resting on parent bodies gives ejection conditions more stringent than previously expected. Finally, a simplified evaluations shows that if secondary emission properties of ring particle are of the order of those of many other oxides, and if the plasma temperature is near one of their threshold temperatures, then a very small environmental variation can trigger the ejection of about 0.1- to 1-μm grains from about 1-mm to 10-cm parent bodies in a very short time scale.     

The contribution of icy grains to the activity of comets: I. Grain lifetime and distribution

We have developed a computer code (GEM—grain evolution model) to simulate the behavior of ice grains in a comet coma. The grains are assumed to be composed of water-ice with an admixture of dark material (“dirt”). An initial size distribution of grains is assumed to be ejected from the nucleus. The ejected mass is taken to be proportional to the rate of gas production by the nucleus. The efficiency for absorption and re-radiation of sunlight is computed from Mie scattering theory. The grain temperature and sublimation rate at a given heliocentric distance is then derived from energy balance considerations. The evolution of the grain size distribution is followed as a function of distance from the nucleus.     

Chemical and physical properties of gas jets in comets: I. Monte Carlo model of an inner cometary coma

We describe a 3-dimensional, time-dependent Monte Carlo model developed to analyze the chemical and physical nature of a cometary gas coma. Our model includes the necessary physics and chemistry to recreate the conditions applicable to Comet Hale-Bopp when the comet was near 1 AU from the Sun. Two base models were designed and are described here. The first is an isotropic model that emits particles (parents of the observed gases) from the entire nucleus; the second is a jet model that ejects parent particles solely from discrete active areas on the surface of the comet nucleus, resulting in coma jets. The two models are combined to produce the final model, which is compared with observations. The physical processes incorporated in both base models include: (1) isotropic ejection of daughter molecules (the observed gases) in the parent's frame of reference, (2) solar radiation pressure, (3) solar insolation effects, (4) collisions of daughter products with other molecules in the coma, and (5) acceleration of the gas in the coma. The observed daughter molecules are produced when a parent decays, which is represented by either an exponential decay distribution (photodissociation of the parent gas) or a triangular distribution (production from a grain extended source). Application of this model to the analysis the OH, C₂ and CN gas jets observed in the coma of Comet Hale-Bopp is the focus of the accompanying paper [Lederer, S.M., Campins, H., Osip, D.J., 2008. Icarus, in press (this issue)].     

Infrared photometry of comets Bowell and P/Stephan-Oterma

We report broadband infrared photometry of comets P/Stephan-Oterma and Bowell between 1 and 20 μm. Their JHK colors are similar to P/Meier and P/Tuttle and are compatible with scattering of sunlight by micron-sized grains. The thermal emission from P/Stephan-Oterma showed an effective temperature significantly higher than that expected from a blackbody in equilibrium. The thermal emission can be models be fit by models of the dust coma consisting of micron-sized grains. Most of the flux at all observed wavelengths comes from the dust grains rather than form the nucleus.     

Dust coma of Comet C/1999 S4 (LINEAR): imaging polarimetry during nucleus disruption

Imaging and polarimetry of Comet C/1999 S4 (LINEAR) during its disruption provide information about the physical properties of the scattering dust particles, and some insight into the structure of the nucleus. A significant decrease in the brightness was noticed, together with a drastic change in the shape of the dust coma. The whole-coma polarization increased, which was typical of a comet with a near 27 percent maximum in polarization, the increase being comparable to previous observations for comets suffering a limited fragmentation. An important gradient in the intensity on the solar side corresponds to the ejected material. The degree of polarization in this region is higher than generally observed in jets and it increases with time as the nucleus (or its fragments) breaks up and ejects relatively large and compact particles. In the surrounding coma, these large particles are fragmented on short time-scales, indicated by the decrease of polarization. These results suggest that the fragile nucleus was not, as far as the physical properties of the dust are concerned, differentiated, and that it was possibly built of primordial cometesimals originating from the same formation region.     

On the Relationship of Chemical Abundances in the Nucleus to Those in the Coma

One of the goals of comet research is the determination of the chemical composition of the nucleus because it provides us with the clues about the composition of the nebula in which comet nuclei formed. It is well accepted that photo-chemical reactions must be considered to establish the abundances of mother molecules in the coma as they are released from the comet nucleus or from distributed dust sources in the coma. However, the mixing ratios of mother molecules in the coma changes with heliocentric distance. To obtain the abundances in the nucleus relative to those in the coma, we must turn our attention to the release rates of mother molecules from the nucleus as a function of heliocentric distance. For this purpose, we assume three sources for the coma gas: the surface of the nucleus (releasing mostly water vapor), the dust in the coma (the distributed source of several species released from dust particles), and the interior of the porous nucleus (the source of many species more volatile than water). The species diffusing from the interior of the nucleus are released by heat transported into the interior. Thus, the ratio of volatiles relative to water in the coma is a function of the heliocentric distance and provides important information about the chemical composition and structure of the nucleus. Our goal is to determine the abundance ratios of various mother molecules relative to water from many remote-sensing observations of the coma as a function of heliocentric distance. Comet Hale-Bopp is ideal for this purpose since it has been observed using instruments in many different wavelength regions over large ranges of heliocentric distances. The ratios of release rates of species into the coma are than modeled assuming various chemical compositions of the spinning nucleus as it moves from large heliocentric distance through perihelion. Since the heat flow into the nucleus will be different after perihelion from that before perihelion, we can also expect different gas release rates after perihelion compared to those observed before perihelion. Since not all the data are available yet, we report on progress of these calculations. This revised version was published online in July 2006 with corrections to the Cover Date.     

A multi-fluid model of an H2O-dominated dusty cometary atmosphere

A self-consistent multi-fluid solution of the dynamical and thermal structure of an H₂O-dominated, two-phase dusty-gas cometary atmosphere has been obtained by solving the simultaneous set of differential equations representing conservation of number density, momentum and energy, together with the transfer of solar radiation in streams responsible for the major photolytic processes and the heating of the nucleus. The validity of this model, as in the earlier single-fluid ones, is restricted to the collision-dominated region where all the heavy species (ions and neutrals) are assumed to achieve a common temperature and velocity. However, recognizing that the photo-produced hydrogen is rather inefficient in exchanging energy with the heavier species we treat the hydrogen separately: it is assumed to be composed of a thermalized component (the second fluid) and a pre-thermal component.The present model, which is transonic due to the presence of the dust in the inner coma, causes the heavy species to expand subsonically from the nucleus and to smoothly traverse the sonic point within about 45 m of the nucleus, although the dust-gas coupling persists to about 50 km. While the temperature of the heavy species goes through a strong inversion within about 100 km from the nucleus, due to the effects of IR cooling and expansion, it increases to about 300–400 K in the outermost part of the collision-dominated coma due to UV photolytic heating. These temperatures are smaller by a factor of 2–3 from the predictions of the earlier single-fluid models, which assumed instant thermalization of the photo-produced hydrogen.While the velocities of the heavy species and the thermal hydrogen increase to, respectively, 1.1 km s^–1 and 1.6 km s^–1 in the outer (collisional) coma, the velocity of the pre-thermal component reaches about 15 km s^–1. This latter value is consistent with Ly- observations of a number of comets, which implies a fast (20 km s^–1) hydrogen component in the outer coma. The boundary of the exosphere, where the non-thermal hydrogen dominates, is predicted to be around 1.5×10⁴ km from the nucleus. The calculations are for a comet of radius 2.5 km with a dust/gas ratio of 1, at a heliocentric distance of 1 AU.     

Comet Splitting – Observations and Model Scenarios

Splitting events affect cometary nuclei to a different level of severity ranging from complete disruption of the nucleus (e.g., C/1999 S4 LINEAR) to separation of major fragments (e.g., 73P/Schwassmann-Wachmann 3) and spill-offs of smaller boulders (e.g., C/2001 A2 LINEAR).Fragmentation of comets produces secondary products over a wide range of sizes (from cometesimals to sub-micron dust). It is detectable through the presence of fragments (with own comae and tails) in the coma of the parent nucleus, through outbursts in its activity and through arc-lets (“coma wings”)associated with fragments. The secondaries have different life times and show different non-gravitational forces. Nucleus splitting is also considered to generate whole families of comets (Kreutz group) or — if gravitational bound — multiple nuclei (e.g., C/1995 O1 Hale-Bopp). It may explain the striae phenomena seen in dust tails of bright comets (C/1995 O1 Hale-Bopp) and the detection of chains of impact craters onother bodies in the solar system. As process of significant mass loss it is relevant for the scenario of nucleus extinction, at the same time it also plays a role for the number statistics of existing (observable) comets and for the size distribution of comet nuclei. Various model scenarios for nucleus splitting are proposed: tidal disruption, rotational splitting, break-up due to internal gas pressure, fragmentation due to collision with other bodies. Only in one case, Comet D/1993 F1Shoemaker-Levy 9, the physical process of fragmentation could be undoubtedly identified. In any case, comet splitting provides important insights inthe internal structure, surface layering and chemistry of comet nuclei.     

Nucleus and tail studies of comet P/Swift-tuttle

CCD images of comet P/Swift-Tuttle, obtained in April 1994 with the 2.2m telescope at ESO La Silla/Chile, showed a comaless stellar nucleus. From absolute photometry we estimated the equivalent radius of the cometary nucleus to be about 11 km (assuming an albedo of 0.04 as for P/Halley) for two rotation phase angles which differ by about 75 deg. From that we conclude that the nucleus is either of rather spherical shape or that the viewing geometry was almost pole-on during our observations.An analysis of the plasma tail and inner coma of the comet by means of photographic plates and CCD images through IHW and BVR filters, obtained with the 80cm Schmidt camera and the 1.2m telescope at Calar Alto/Spain in November 1992, revealed several tail rays, head streamers and substructures in brightness excess areas in the coma. While some of the tail rays extended to several million km nuclear distance, most of them can be traced to starting points which lie in a region just 20000–35000 km projected distance tailward from the nucleus.     

The destruction of cometary grains and changes in the luminosity of comets

One explanation of the sudden changes in the brightness of comets is proposed based on the author's earlier suggestions involving the fragmentation of cometary grains. Within the inner coma, a core‐mantle model of the structure of grains is assumed. The proposed mechanism is a combination of electrostatic stress and thermodynamical fragmentation of the cometary grains water‐ice mantle. It has been shown that the vapour pressure of volatile inclusions placed in the waterice mantle of grains can increase sufficiently to cause their fragmentation. It takes place before grains can completely sublime into the vacuum away. Numerical calculations have been carried out for a large range of values of probable physical characteristics of cometary material. The proposed approach yields increases in cometary brightness consistent with observations of typical cometary outbursts. It is concluded that this approach can provide an explanation of the sudden change in activity of comets for a wide range of heliocentric distances (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)