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We discuss the synergies between heliospheric and dust science, the open science questions, the technological endeavors and programmatic aspects that are important to maintain or develop in the decade to come. In particular, we illustrate how we can use interstellar dust in the solar system as a tracer for the (dynamic) heliosphere properties, and emphasize the fairly unexplored, but potentially important science question of the role of cosmic dust in heliospheric and astrospheric physics. We show that an Interstellar Probe mission with a dedicated dust suite would bring unprecedented advances to interstellar dust research, and can also contribute-through measuring dust - to heliospheric science. This can, in particular, be done well if we work in synergy with other missions inside the solar system, thereby using multiple vantage points in space to measure the dust as it `rolls' into the heliosphere. Such synergies between missions inside the solar system and far out are crucial for disentangling the spatially and temporally varying dust flow. Finally, we highlight the relevant instrumentation and its suitability for contributing to finding answers to the research questions., Comment: 18 pages, 7 Figures, 5 Tables. Originally submitted as white paper for the National Academies Decadal Survey for Solar and Space Physics 2024-2033

Accretion processes in protoplanetary disks produce a diversity of small bodies that played a crucial role in multiple reshuffling events throughout the solar system and in both early and late accretion of planets. Application of thermo-chronometers to meteorites provides precise dating of the formation age of mineralogical components. Nucleosynthetic anomalies indicating a dichotomy between NC and C meteorites and precise parent body (PB) chronology can be combined with thermal evolution models to constrain the timescale of accretion and dynamical processes in the early solar system. Achondrite PBs are considered to have accreted early and mostly in the NC region, while late accretion in the C region produced mostly undifferentiated PBs, such as the CR chondrite PB that formed as late as 4 Ma after CAIs. However, presence of more evolved CR-related meteorites suggests also an earlier accretion timing. We present modeling evidence for a temporally distributed accretion of parent bodies of CR-related meteorite groups that originate from a C reservoir and range from aqueously altered chondrites to partially differentiated primitive achondrites. The PB formation times derived range from <1 Ma to ~4 Ma after solar system formation, with ~3.7 Ma, ~1.5-2.75 Ma, <~0.6 Ma, and <~0.7 Ma for CR, Flensburg, NWA 6704, and NWA 011. This implies that accretion processes in the C reservoir started as early as in the NC reservoir and produced differentiated PBs with carbonaceous compositions in addition to undifferentiated C chondritic PBs. The accretion times correlate inversely with the degree of the meteorites' alteration, metamorphism, or differentiation. Accretion times for CI/CM, Ryugu, and Tafassites PBs of ~3.75 Ma, ~1-3 Ma, and 1.1 Ma, respectively, fit well into this correlation in agreement with the thermal and alteration conditions suggested by the meteorites.

The history of accretion and differentiation processes in the planetesimals is provided by various groups of meteorites. Sampling different parent body layers, they reveal the circumstances of the metal-silicate segregation and the internal structures of the protoplanets. The ungrouped achondrite Erg Chech 002 (EC 002) added to the suite of samples from primitive igneous crusts. Here we present models that utilize thermo-chronological data for EC 002 and fit the accretion time and size of its parent body to these data. The U-corrected Pb-Pb, Al-Mg, and Ar-Ar ages used imply a best-fit planetesimal with a radius of 20-30 km that formed at 0.1 Ma after CAIs. Its interior melted early and differentiated by 0.5 Ma, allowing core and mantle formation with a transient lower mantle magma ocean, and a melt fraction of <25 % at the meteorite layering depth. EC 002 formed from this melt at a depth of 0.8 km in a partially differentiated region covered by an undifferentiated crust. By simulating collisions with impactors of different sizes and velocities, we analyzed the minimum ejection conditions of EC 002 from its original parent body and the surface composition of the impact site. The magma ocean region distinct from the layering depth of EC 002 implyes that it was not involved in the EC 002 genesis. Our models estimate closure temperatures for the Al-Mg ages as 1060 K to 1200 K. A fast parent body cooling attributes the late Ar-Ar age to a local reheating by another, late impact.

Low-albedo asteroids preserve a record of the primordial solar system planetesimals and the conditions in which the solar nebula was active. However, the origin and evolution of these asteroids are not well-constrained. Here we measured visible and near-infrared (0.5 - 4.0 microns) spectra of low-albedo asteroids in the mid-outer main belt. We show that numerous large (d > 100 km) and dark (geometric albedo < 0.09) asteroids exterior to the dwarf planet Ceres' orbit share the same spectral features, and presumably compositions, as Ceres. We also developed a thermal evolution model that demonstrates that these Ceres-like asteroids have highly-porous interiors, accreted relatively late at 1.5 - 3.5 Myr after the formation of calcium-aluminum-rich inclusions, and experienced maximum interior temperatures of < 900 K. Ceres-like asteroids are localized in a confined heliocentric region between 3.0 - 3.4 au but were likely implanted from more distant regions of the solar system during the giant planet's dynamical instability.

Observations of C-type NEAs and lab investigations of carbonaceous chondritic (CC) meteorites provide strong evidence for a high porosity of C-type asteroids. Boulder microporosity values derived from in-situ measurements at the surface of the rubble-pile NEA Ryugu of up to 55% are substantially higher than for water-rich CC samples and could indicate distinct evolution paths for the parent body of Ryugu and parent bodies of carbonaceous chondrites, despite spectral similarities. In the present study, we calculate the evolution of the temperature and porosity for early solar system's planetesimals in order to constrain the range of parameters that result in microporosities compatible with Ryugu's high-porosity material and likely burial depths for the boulders observed at the surface. By varying key properties of the parent body, such as accretion time t0 and radius R that have strong influence on temperature and porosity and by comparing the interior porosity distribution with the measured boulder microporosity, hydration, and partial dehydration of the material, we constrain a field within the (R,t0)-space appropriate for bodies that are likely to have produced such material. Our calculations indicate a parent body size of only a few km and its early accretion within <~2-3 Myr after the formation of Ca-Al-rich inclusions. A gradual final porosity profile of best-fit bodies indicates production of both low- and high-density boulders from the parent body material. By contrast, parent body properties for CI and CM chondrites obtained by fitting carbonate formation data indicate a radius of ~20-25 km and an accretion time of ~3.75 Myr after CAIs. These results imply a population of km-sized early accreting porous planetesimals as parent bodies of Ryugu (and, potentially, other NEAs) and a population of larger late accreting less porous parent bodies of water-rich carbonaceous chondrites.

Chondrites stem from undifferentiated asteroidal parent bodies that nevertheless experienced a certain degree of metamorphism after their formation in the early solar system. Maximum temperatures of metamorphism depend mainly on formation time and the abundance of the main heating source, which is short-lived 26Al. Enstatite chondrites formed under reducing conditions and include many strongly metamorphosed members of petrologic type 6. We model the thermal evolution of the parent body of the low metal enstatite chondrite class (EL). The model takes into account accretion, heating, sintering and compaction by hot pressing of the initially porous material, temperature dependent heat conductivity, and insulation effects by the remaining regolith layer. Key parameters of the parent body (formation time, radius, and porosity) are estimated by fitting thermal histories of EL6 chondrites (LON 94100, Neuschwanstein, Khairpur, Blithfield, Daniel's Kuil), constrained mainly by I-Xe and Ar-Ar ages and their respective closure temperatures. Viable fits are obtained for parent bodies with 120 -- 210 km radius, formed c. 1.8 -- 2.1 Ma after Ca,Al-rich inclusions (CAIs), and an initial porosity of 30%, relatively independent on initial disk temperatures. Thermal histories of the different EL6 chondrites are indistinguishable and so are their burial depths. While the exact layering depth is somewhat model dependent (c. 12--20 km), the thickness of the layer from which all five EL6 chondrites stem is < 1 km. Hence, an origin from a quite small asteroidal fragment is possible, particular as most excavation ages inferred from cosmic ray exposure data are compatible with a separation as meter sized meteoroids from a small Apollo asteroid 33 Ma ago., Comment: 28 pages, 10 figures, accepted by Icarus

Aims. We tackle the conundrums of organic materials missing from interstellar dust when measured inside the Solar System, while undoubtedly existing in the local interstellar cloud (LIC), which surrounds the Solar System. Methods. We present a theoretical argument that organic compounds sublimate almost instantaneously by exothermic reactions, when solar insolation triggers the recombination of free radicals or the rearrangement of carbon bonds in the compounds. Results. It turns out that the triggering temperature lies in the range of 20$-$50 K by considering that sublimation of organic materials takes place beyond the so-called filtration region of interstellar neutral atoms. We find that in-situ measurements of LIC dust in the Solar System result in an overestimate for the gas-to-dust mass ratio of the LIC, unless the sublimation of organic materials is taken into account. We also find that previous measurements of interstellar pickup ions have determined the total elemental abundances of gas and organic materials, instead of interstellar gas alone. Conclusions. We conclude that LIC organic matter suffers from sublimation en route to the heliosphere, implying that our understanding of LIC dust from space missions is incomplete. Since space missions inside the orbit of Saturn cannot give any information on the organic substances of LIC dust, one must await a future exploration mission to the inner edge of the Oort cloud for a thorough understanding of organic substances in the LIC. Once our model for the sublimation of interstellar organic matter by exothermic chemical reactions of free radicals is confirmed, the hypothesis of panspermia from the diffuse interstellar medium is ruled out., Comment: 9 pages, 6 figures, to appear in Astronomy & Astrophysics

The radius of the L chondrite parent body, its formation time, and its evolution history are determined by fitting theoretical models to empirical data of radioisotopic chronometers for L chondrites. A simplified evolution model for the L chondrite parent body is constructed considering sintering of the initially porous material, temperature dependent heat conductivity, and an insulating regolith layer. Such models are fitted to thermochronological data of five meteorites for which precise data for the Hf-W and U-Pb-Pb thermochronometers have been published. A set of parameters for the L chondrite parent body is found that yields excellent agreement (within error bounds) between a thermal evolution model and thermochonological data. Empirical cooling rate data also agree with the model results within error bounds such that there is no conflict between cooling rate data and the onion-shell model. Two models are found to be compatible with the presently available empirical data: One model with a radius of 115 km and a formation time of 1.89 Ma after CAI formation, another model with 160 km radius and formation time of 1.835 Ma. The central temperature of the smaller body remains well below the Ni,Fe-FeS eutectic melting temperature and is consistent with the apparent non-existence of primitive achondrites related to the L chondrites. For the bigger model incipient melting in the central core region is predicted which opens the possibility that primitive achondrites related to L chondrites could be found., Comment: 22 pages, 11 figures, accepted by Astronomy & Astrophysics

Understanding the compaction and differentiation of the planetesimals and protoplanets from the Asteroid Belt and the terrestrial planet region of the Solar System requires a reliable modeling of their internal thermal evolution. An important ingredient for this is a detailed knowledge of the heat conductivity of the chondritic mixture of minerals and metal in planetesimals. The temperature dependence of the heat conductivity is evaluated here from the properties of its mixture components by a theoretical model. This allows to predict the temperature dependent heat conductivity for the full range of observed meteoritic compositions and also for possible other compositions. For this purpose, published results on the temperature dependence of heat conductivity of the mineral components found in chondritic material are fitted to the model of Callaway for heat conductivity in solids by phonons. For the Ni,Fe-alloy published laboratory data are used. The heat conductivity of chondritic material then is calculated by means of mixing-rules. The role of micro-cracks is studied which increase the importance of wall-scattering for phonon-based heat conductivity. The model is applied to published data on heat conductivity of individual chondrites. The experimental data for the dependence of the heat conductivity on temperature can be reproduced rather well by the model if the heat conductivity is calculated for the composition of the meteorites. It is found that micro-cracks have a significant impact on the temperature dependence of the heat conductivity because of their reduction of phonon scattering length., Comment: 18 pages, 7 figures, accepted by Astronomy & Astrophysics

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7 - 8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 \pm 4 Ma. The results from short-lived radionuclides are compatible with an atmosperic pre-entry radius of 30 - 40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10Be concentration indicates a recent (3 - 5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30 - 35 cm pre-entry radius.

A high fraction of carbon bound in solid carbonaceous material is observed to exist in bodies formed in the cold outskirts of the solar nebula, while bodies in the terrestrial planets region contain nearly none. We study the fate of the carbonaceous material during the spiral-in of matter as the sun accretes matter from the solar nebula. From observational data on the composition of the dust component in comets and interplanetary dust particles, and from data on pyrolysis experiments, we construct a model for the composition of the pristine carbonaceous material in the outer parts of the solar nebula. We study the pyrolysis of the refractory and volatile organic component and the concomitant release of high-molecular-weight hydrocarbons under quiescent conditions of disk evolution where matter migrates inwards. We also study the decomposition and oxidation of the carbonaceous material during violent flash heating events, which are thought to be responsible for the formation of chondrules. It is found that the complex hydrocarbon components are removed from the solid disk matter at temperatures between 250 and 400 K, while the amorphous carbon component survives up to 1200 K. Without efficient carbon destruction during flash-heating associated with chondrule formation the carbon abundance of terrestrial planets, except for Mercury, would be not as low as it is found in cosmochemical studies. Chondrule formation seems to be a process that is crucial for the carbon-poor composition of the material of terrestrial planets., Comment: 17 pages, 7 figures, accepted by Astronomy & Astrophysics

The construction of models for the internal constitution and the temporal evolution of large planetesimals, the parent bodies of chondrites, requires information on the heat conductivity of the complex mixture of minerals and iron metal found in chondrites. It is attempted to evaluate the heat conductivity of a multi-component mineral mixture and granular medium from the heat conductivities of its mixture components. Random mixtures of solids with chondritic composition and packings of spheres are numerically generated. The heat conduction equation is solved in high spatial resolution for a test cube filled with such matter. From the heat flux through the cube the heat conductivity of the mixture is derived. The model results for porous material are consistent with data for compacted sandstone, but are at odds with measurements for H and L chondrites. The discrepancy is traced back to shock modification of the currently available meteoritic material by impacts on the parent body over the last 4.5 Ga. This causes numerous micro-cracks that act as additional barriers for heat transfer. The void structure in meteorites is different from that which probably existed in the pristine material of the parent bodies. The results obtained for the heat conductivity of the pristine material are used for calculating models for the evolution of the H chondrite parent body which are fitted to the cooling data of a number of H chondrites. The fit to the data good., Comment: 19 pages, 8 figures, accepted by Astronomy & Astrophysics

COSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has been designed to measure the composition of cometary dust grains. It has a mass resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination of inorganic mass peaks from organic ones in the mass spectra. We have evaluated the identification capabilities of the reference model of COSIMA for inorganic compounds using a suite of terrestrial minerals that are relevant for cometary science. Ground calibration demonstrated that the performances of the flight model were similar to that of the reference model. The list of minerals used in this study was chosen based on the mineralogy of meteorites, interplanetary dust particles and Stardust samples. It contains anhydrous and hydrous ferromagnesian silicates, refractory silicates and oxides (present in meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the analyses of these minerals, we have calculated relative sensitivity factors for a suite of major and minor elements in order to provide a basis for element quantification for the possible identification of major mineral classes present in the cometary grains., Comment: 20 pages, 3 figures, 5 tables

Reconstruction of the thermal history of individual meteorites which can be assigned to the same parent body allows to derive general characteristics of the parent body, which hold important clues on the planetary formation process. This requires to construct models for the heating of such bodies by short lived radioactives, in particular by 26Al, and its cooling by heat conduction, which then are compared with the cooling histories of the meteorites. The heat conductivity of the planetesimal material depends critically on the porosity of the chondritic material and changes by sintering of the material at elevated temperatures and pressures. Compaction of a granular material is a key process for the thermal history of the parent bodies of meteorites. The modelling of the compaction process is improved by applying concepts originally developed for hot isostatic pressing in metallurgical processes. It is extended to a binary mixture of matrix and chondrules, as observed in chondrites. By comparison with published data on sintering experiments it is shown that the algorithm allows a sufficiently accurate modelling of the compaction of silicate material. It is shown that the characteristic temperature at which sintering occurs is different for matrix or chondrule dominated precursor material. We apply the new method to model the thermal evolution of the parent body of the H chondrites and determine an improved optimized set of model parameters for this body., Comment: 18 pages, 6 figures

Mercury's high uncompressed mass density suggests that the planet is largely composed of iron, either bound within metal (mainly Fe-Ni), or iron sulfide. Recent results from the MESSENGER mission to Mercury imply a low temperature history of the planet which questions the standard formation models of impact mantle stripping or evaporation to explain the high metal content. Like Mercury, the two smallest extrasolar rocky planets with mass and size determination, CoRoT-7b and Kepler-10b, were found to be of high density. As they orbit close to their host stars this indicates that iron rich inner planets might not be a nuisance of the solar system but be part of a general scheme of planet formation. From undifferentiated chondrites it is also known that the metal to silicate ratio is highly variable which must be ascribed to pre-planetary fractionation processes. Due to this fractionation most chondritic parent bodies - most of them originated in the asteroid belt - are depleted in iron relative to average solar system abundances. The astrophysical processes leading to metal silicate fractionation in the solar nebula are essentially unknown. Here, we consider photophoretic forces. As these forces particularly act on irradiated solids, they might play a significant role for the composition of planetesimals forming at the inner edge of protoplanetary discs. Photophoresis can separate high thermal conductivity materials (iron) from lower thermal conductivity solids (silicate). We suggest that the silicates are preferentially pushed into the optical thick disk. Subsequent planetesimal formation at the edge moving outwards leads to metal rich planetesimals close to the star and metal depleted planetesimals further out in the nebula.

Silicate minerals belong to the most abundant solids in space. Their formation becomes difficult at the transition from the oxygen rich chemistry of M-stars to the carbon rich chemistry of C-stars. In the intermediate type S-stars oxygen and carbon are consumed by CO and SiO molecule formation, and left-over oxygen to build the SiO4-tetrahedra of silicates becomes scarce. Then SiO molecules may directly condense into solid SiO. The IR absorption spectrum of solid SiO differs from that of silicates by the absence of Si-O-Si bending modes at 18 mum while the absorption by Si-O bond stretching modes at 10 mum is present. Such characteristics are observed in a number of S-star spectra. We suggest that this observation may be explained by formation of solid SiO as a major dust component at C/O abundance ratios close to unity. We determine the IR absorption properties of solid SiO by laboratory transmission measurements of thin SiO films produced by vapour deposition on a Si(111) wafer. From the measured spectra the dielectric function of SiO is derived. The results are used in model calculations of radiative transfer in circumstellar dust shells with solid SiO dust. Comparison of synthetic and observed spectra shows that reasonable agreement is obtained between the main spectral characteristics of emission bands due to solid SiO and an emission band centred on 10 mum, but without accompanying 18 mum band, observed in some S-stars. We propose that solid SiO is the carrier material of this 10 mum spectral feature.

The cooling histories of individual meteorites can be empirically reconstructed by using ages from different radioisotopic chronometers with distinct closure temperatures. For a group of meteorites derived from a single parent body such data permit the reconstruction of the cooling history and properties of that body. Particularly suited are H chondrites because precise radiometric ages over a wide range of closure temperatures are available. A thermal evolution model for the H chondrite parent body is constructed by using all H chondrites for which at least three different radiometric ages are available. Several key parameters determining the thermal evolution of the H chondrite parent body and the unknown burial depths of the H chondrites are varied until an optimal fit is obtained. The fit is performed by an 'evolution algorithm'. Empirical data for eight samples are used for which radiometric ages are available for at least three different closure temperatures. A set of parameters for the H chondrite parent body is found that yields excellent agreement (within error bounds) between the thermal evolution model and empirical data of six of the examined eight chondrites. The new thermal model constrains the radius and formation time of the H chondrite parent body (possibly (6) Hebe), the initial burial depths of the individual H chondrites, the average surface temperature of the body, the average initial porosity of the material the body accreted from, and the initial 60Fe content of the H chondrite parent body., Comment: 16 pages, 7 figures

The major aim of this study is to assess the effects of sintering of initially porous material on the thermal evolution of planetesimals, and to constrain the values of basic parameters that determined the structure and evolution of the H chondrite parent body. A new code is presented for modeling the thermal evolution of ordinary chondrite parent bodies that initially are highly porous and undergo sintering by hot pressing as they are heated by decay of radioactive nuclei. The pressure and temperature stratification in the interior of the bodies is calculated by solving the equations of hydrostatic equilibrium and energy transport. The decrease of porosity of the granular material by hot pressing due to self-gravity is followed by solving a set of equations for the sintering of powder materials. For the heat conductivity of granular material we combine recently measured data for highly porous powder materials, relevant for the surface layers of planetesimals, with data for heat conductivity of chondrite material, relevant for the strongly sintered material in deeper layers. To demonstrate the capability of our new model, the thermal evolution of the H chondrite parent body was reconstructed. The model starts with a porous body that is later compacted first by 'cold pressing' at low temperatures and then by 'hot pressing' for temperatures above \approx 700 K, i.e., the threshold temperature for sintering of silicates. The thermal model was fitted to the well constrained cooling histories of the two H chondrites Kernouve (H6) and Richardton (H5)., Comment: 19 pages 12 figures submitted to A&A

We present a non-invasive technique for measuring the thermal conductivity of fragile and sensitive materials. In the context of planet formation research, the investigation of the thermal conductivity of porous dust aggregates provide important knowledge about the influence of heating processes, like internal heating by radioactive decay of short-lived nuclei, e.g. 26Al, on the evolution and growth of planetesimals. The determination of the thermal conductivity was performed by a combination of laboratory experiments and numerical simulations. An IR camera measured the temperature distribution of the sample surface heated by a well-characterized laser beam. The thermal conductivity as free parameter in the model calculations, exactly emulating the experiment, was varied until the experimental and numerical temperature distributions showed best agreement. Thus, we determined for three types of porous dust samples, consisting of spherical, micrometer-sized SiO2 particles, with volume filling factors in the range of 15% to 54%, the thermal conductivity to be 0.002 to 0.02 W/(m*K), respectively. From our results, we can conclude that the thermal conductivity mainly depends on the volume filling factor. Further investigations, which are planned for different materials and varied contact area sizes (produced by sintering), will prove the appropriate dependencies in more detail., Comment: accepted by Icarus

The abundance evolution of interstellar dust species originating from stellar sources and from condensation in molecular clouds in the local interstellar medium of the Milky Way is studied and the input of dust material to the Solar System is determined. A one-zone chemical evolution model of the Milky Way for the elemental composition of the disk combined with an evolution model for its interstellar dust component similar to that of Dwek (1998) is developed. The dust model considers dust-mass return from AGB stars as calculated from synthetic AGB models combined with models for dust condensation in stellar outflows. Supernova dust formation is included in a simple parameterized form which is gauged by observed abundances of presolar dust grains with supernova origin. For dust growth in the ISM a simple method is developed for coupling this with disk and dust evolution models. The time evolution of the abundance of the following dust species is followed in the model: silicate, carbon, silicon carbide, and iron dust from AGB stars and from SNe as well as silicate, carbon, and iron dust grown in molecular clouds. It is shown that the interstellar dust population is dominated by dust accreted in molecular clouds; most of the dust material entering the Solar System at its formation does not show isotopic abundance anomalies of the refractory elements, i.e., inconspicuous isotopic abundances do not point to a Solar System origin of dust grains. The observed abundance ratios of presolar dust grains formed in SN ejecta and in AGB star outflows requires that for the ejecta from SNe the fraction of refractory elements condensed into dust is 0.15 for carbon dust and is quite small ($\sim10^{-4}$) for other dust species., Comment: 29 pages, 19 figures