Planetesimal Collisions Research Articles

Complementary nucleosynthetic isotope anomalies of Mo and W in chondrules and matrix in the Allende carbonaceous chondrite: The case for hydrothermal metamorphism and its implications

AbstractThe remarkable complementary isotopic relationship in the Allende chondrite between chondrules (depleted in s‐process molybdenum and tungsten) and matrix (enriched in these nuclides) has been interpreted as evidence that the anomalies were established during chondrule formation, and that chondrules were, therefore, not made by planetesimal collisions. We question this interpretation, and to better understand the complementary relationship, we review nucleosynthetic isotopic variations of Mo and W in bulk carbonaceous chondrites, their components, and acid leachates extracted from them. Mo isotopic data almost always track a mixing line between pure s‐process Mo and s‐process‐depleted Mo (i.e., with excess p‐process and r‐process Mo in a fixed ratio). Tungsten data track an equivalent mixing line. Guided by our review, we develop a model suggesting how the isotopic variations in Allende’s chondrules and matrix could be attributable to hydrothermal alteration in the parent body. In our model, anomalous Mo and W, both depleted in s‐process isotopes, are easily leached from their carriers in the matrix, then transported in solution and precipitated preferentially in water‐deficient components, such as chondrules, where the aqueous solvent is consumed. The model operates after accretion so does not inform chondrule‐forming mechanisms. It also goes some way to explaining variations of Mo and W isotopes in Ca‐Al‐rich inclusions in Allende, and variations of s‐process Mo in bulk carbonaceous chondrites.

Extreme Variability of the V488 Persei Debris Disk

Abstract V488 Persei is the most extreme debris disk known in terms of the fraction of the stellar luminosity it intercepts and reradiates. The infrared output of its disk is extremely variable, similar in this respect to the most variable disk known previously, that around ID8 in NGC 2547. We show that the variations are likely to be due to collisions of large planetesimals (≳100 km in diameter) in a belt being stirred gravitationally by a planetary or low-mass-brown-dwarf member of a planetary system around the star. The dust being produced by the resulting collisions is falling into the star due to drag by the stellar wind. The indicated planetesimal destruction rate is so high that it is unlikely that the current level of activity can persist for much longer than ∼1000–10,000 yr and it may signal a major realignment of the configuration of the planetary system.

Planet formation in stellar binaries: global simulations of planetesimal growth

Planet formation around one component of a tight, eccentric binary system such as γ Cephei (with semimajor axis around 20 AU) is theoretically challenging because of destructive high-velocity collisions between planetesimals. Despite this fragmentation barrier, planets are known to exist in such (so-called S-type) orbital configurations. Here we present a novel numerical framework for carrying out multi-annulus coagulation-fragmentation calculations of planetesimal growth, which fully accounts for the specifics of planetesimal dynamics in binaries, details of planetesimal collision outcomes, and the radial transport of solids in the disk due to the gas drag-driven inspiral. Our dynamical inputs properly incorporate the gravitational effects of both the eccentric stellar companion and the massive non-axisymmetric protoplanetary disk in which planetesimals reside, as well as gas drag. We identify a set of disk parameters that lead to successful planetesimal growth in systems such as γ Cephei or α Centauri starting from 1 to 10 km size objects. We identify the apsidal alignment of a protoplanetary disk with the binary orbit as one of the critical conditions for successful planetesimal growth: It naturally leads to the emergence of a dynamically quiet location in the disk (as long as the disk eccentricity is of order several percent), where favorable conditions for planetesimal growth exist. Accounting for the gravitational effect of a protoplanetary disk plays a key role in arriving at this conclusion, in agreement with our previous results. These findings lend support to the streaming instability as the mechanism of planetesimal formation. They provide important insights for theories of planet formation around both binary and single stars, as well as for the hydrodynamic simulations of protoplanetary disks in binaries (for which we identify a set of key diagnostics to verify).

Collision rates of planetesimals near mean-motion resonances

ABSTRACT In circumstellar discs, collisional grinding of planetesimals produces second-generation dust. While it remains unclear whether this ever becomes a major component of the total dust content, the presence of such dust, and potentially the substructure within it, can be used to explore a disc’s physical conditions. A perturbing planet produces non-axisymmetric structures and gaps in the dust, regardless of its origin. The dynamics of planetesimals, however, will be very different than that of small dust grains due to weaker gas interactions. Therefore, planetesimal collisions could create dusty disc structures that would not exist otherwise. In this work, we use N-body simulations to investigate the collision rate profile of planetesimals near mean-motion resonances. We find that a distinct bump or dip feature is produced in the collision profile, the presence of which depends on the libration width of the resonance and the separation between the peri- and apocentre distances of the edges of the resonance. The presence of one of these two features depends on the mass and eccentricity of the planet. Assuming that the radial dust emission traces the planetesimal collision profile, the presence of a bump or dip feature in the dust emission at the 2:1 mean-motion resonance can constrain the orbital properties of the perturbing planet. This assumption is valid, so long as radial drift does not play a significant role during the collisional cascade process. Under this assumption, these features in the dust emission should be marginally observable in nearby protoplanetary discs with ALMA.

Constraining planetesimal stirring: how sharp are debris disc edges?

ABSTRACT The dust production in debris discs by grinding collisions of planetesimals requires their orbits to be stirred. However, stirring levels remain largely unconstrained, and consequently the stirring mechanisms as well. This work shows how the sharpness of the outer edge of discs can be used to constrain the stirring levels. Namely, the sharper the edge the lower the eccentricity dispersion must be. For a Rayleigh distribution of eccentricities (e), I find that the disc surface density near the outer edge can be parametrized as tanh [(rmax − r)/lout], where rmax approximates the maximum semimajor axis and lout defines the edge smoothness. If the semimajor axis distribution has sharp edges erms is roughly 1.2lout/rmax or erms = 0.77lout/rmax if semimajor axes have diffused due to self-stirring. This model is fitted to Atacama Large Millimeter/submillimeter Array data of five wide discs: HD 107146, HD 92945, HD 206893, AU Mic, and HR 8799. The results show that HD 107146, HD 92945, and AU Mic have the sharpest outer edges, corresponding to erms values of 0.121 ± 0.05, $0.15^{+0.07}_{-0.05}$, and 0.10 ± 0.02 if their discs are self-stirred, suggesting the presence of Pluto-sized objects embedded in the disc. Although these stirring values are larger than typically assumed, the radial stirring of HD 92945 is in good agreement with its vertical stirring constrained by the disc height. HD 206893 and HR 8799, on the other hand, have smooth outer edges that are indicative of scattered discs since both systems have massive inner companions.

Linking planetary embryo formation to planetesimal formation

Context.The accretion of pebbles onto planetary cores has been widely studied in recent years and is found to be a highly effective mechanism for planetary growth. While most studies assume planetary cores as an initial condition in their simulation, the question of the manner, location, and time at which these cores form is often neglected.Aims.We study the effect of pebble accretion during the formation phase and subsequent evolution of planetary embryos in the early stages of circumstellar disk evolution. In doing so, we aim to quantify the timescales and local dependence of planetary embryo formation based on the solid evolution of the disk.Methods.We connected a one-dimensional two-population model for solid evolution and pebble-flux-regulated planetesimal formation to theN-body code LIPAD. We focused on the growth of planetesimals with an initial size of 100 km in diameter by planetesimal collisions and pebble accretion for the first one million years of a viscously evolving disk. We compared 18 differentN-body simulations in which we varied the total planetesimal mass after one million years, the surface density profile of the planetesimal disk, the radial pebble flux, and the possibility of pebble accretion.Results.Pebble accretion leads to the formation of fewer but substantially more massive embryos. The area of possible embryo formation is weakly affected by the accretion of pebbles, and the innermost embryos tend to form slightly earlier than in simulations in which pebble accretion is neglected.Conclusions.Pebble accretion strongly enhances the formation of super-Earths in the terrestrial planet region, but it does not enhance the formation of embryos at larger distances.

Colliding in the Shadows of Giants: Planetesimal Collisions during the Growth and Migration of Gas Giants

Abstract Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal–planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions. In contrast, we find that giant planet migration induces large numbers of high-velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals and to cause disruption of the bodies. New bodies may form from impact debris. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt. A small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. We identify important consequences of planetesimal collisions that have not been considered in planet accretion models. The prevalence of high-velocity collisions during giant planet migration, and their potential links to the properties of meteorites and the formation of chondrules, makes impact vaporization a critically important phenomenon. The consequences of vaporizing planetesimal constituents require further detailed study. New collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed.

Did nuclear transformations inside Earth form nitrogen, oxygen, and water?

Nitrogen and sea water concentrations have increased continuously from the Archean era. A rapid rise in oxygen concentration has been recorded from around 0.8 billion years ago. These phenomena cannot be completely explained by the collision of planetesimals with abundant nitrogen and the late veneer heavy bombardment of comets and meteorites with abundant water, and photosynthesis of heterotrophic plants, respectively. The formation of nitrogen, oxygen, and water are postulated to be the result of an endothermic nuclear transformation of carbon and oxygen nuclei confined in the carbonate aragonite lattice of Earth’s mantle or crust at high temperatures and pressures. This process was likely influenced by excited electrons generated by stick sliding during the evolution of supercontinents, mantle convection triggered by collisions of major asteroids, and nuclear fusion in Earth’s core. Thus, we show that calcium carbonates may have played a crucial role in the generation of atmosphere and sea water in Earth’s history.

Observability of dusty debris discs around M-stars

ABSTRACT Debris discs are second-generation dusty discs formed by collisions of planetesimals. Many debris discs have been found and resolved around hot and solar-type stars. However, only a handful have been discovered around M-stars, and the reasons for their paucity remain unclear. Here, we check whether the sensitivity and wavelength coverage of present-day telescopes are simply unfavourable for detection of these discs or if they are truly rare. We approach this question by looking at the Herschel/DEBRIS survey that has searched for debris discs including M-type stars. Assuming that these cool-star discs are ‘similar’ to those of the hotter stars in some sense (i.e. in terms of dust location, temperature, fractional luminosity, or mass), we check whether this survey should have found them. With our procedure we can reproduce the $2.1^{+4.5}_{-1.7}$ per cent detection rate of M-star debris discs of the DEBRIS survey, which implies that these discs can indeed be similar to discs around hotter stars and just avoid detection. We then apply this procedure to IRAM NIKA-2 and ALMA bands 3, 6, and 7 to predict possible detection rates and give recommendations for future observations. We do not favour observing with IRAM, since it leads to detection rates lower than for the DEBRIS survey, with 0.6–4.5 per cent for a 15 min observation. ALMA observations, with detection rates 0.9–7.2 per cent, do not offer a significant improvement either, and so we conclude that more sensitive far-infrared and single dish sub-millimetre telescopes are necessary to discover the missing population of M-star debris discs.

Collisions of planetesimals from different parts of the feeding zone the terrestrial planets with the forming planets and the Moon embryo

Collisions of planetesimals from different parts of the feeding zone the terrestrial planets with the forming planets and the Moon embryo

Tidal disruption versus planetesimal collisions as possible origins for the dispersing dust cloud around Fomalhaut

Recent analysis suggests that the faint optical point source observed around Fomalhaut from 2004–2014 (Fomalhaut b) is gradually fading and expanding, supporting the case that it may be a dispersing dust cloud resulting from the sudden disruption of a planetesimal. These types of disruptions may arise from catastrophic collisions of planetesimals, which are perturbed from their original orbits in the Fomalhaut dust ring by nearby giant planets. However, disruptions can also occur when the planetesimals pass within the tidal disruption field of the planet(s) that perturbed them in the first place, similar to the Shoemaker-Levy event observed in the Solar System. Given that a gravitationally focusing giant planet has a much larger interaction cross-section than a planetesimal, tidal disruption events can match or outnumber planetesimal collision events in realistic regions of parameter space. Intriguingly, the Fomalhaut dust cloud offers an opportunity to directly distinguish between these scenarios. A tidal disruption scenario leads to a very specific prediction of ephemerides for the planet causing the event. At a most probable mass of 66 M⊕, a semi-major axis of 117 AU, and a system age of 400–500 Myr, this planet would be readily detectable with the James Webb Space Telescope. The presence or absence of this planet at the specific, predicted position is therefore a distinctive indicator of whether the dispersing cloud originated from a collision of two planetesimals or from the disruption of a planetesimal in the tidal field of a giant planet.

Sierra Gorda 009: A new member of the metal‐rich G chondrites grouplet

AbstractWe investigated the metal‐rich chondrite Sierra Gorda (SG) 009, a member of the new G chondrite grouplet (also including NWA 5492, GRO 95551). G chondrites contain 23% metal, very reduced silicates, and rare oxidized mineral phases (Mg‐chromite, FeO‐rich pyroxene). G chondrites are not related to CH‐CB chondrites, based on bulk O, C, and N isotopic compositions, mineralogy, and geochemistry. G chondrites have no fine‐grained matrix or matrix lumps enclosing hydrated material typical for CH‐CB chondrites. G chondrites’ average metal compositions are similar to H chondrites. Siderophile and lithophile geochemistry indicates sulfidization and fractionation of the SG 009 metal and silicates, unlike NWA 5492 and GRO 95551. The G chondrites have average O isotopic compositions Δ17O>0‰ ranging between bulk enstatite (E) and ordinary (O) chondrites. An Al‐rich chondrule from SG 009 has Δ17O>0‰ indicating some heterogeneity in oxygen isotopic composition of G chondrite components. SG 009’s bulk carbon and nitrogen isotopic compositions correspond to E and O chondrites. Neon isotopic composition reflects a mixture of cosmogenic and solar components, and cosmic ray exposure age of SG 009 is typical for O, E, and R chondrites. G chondrites are closely related to O, E, and R chondrites and may represent a unique metal‐rich parent asteroid containing primitive and fractionated material from the inner solar system. Oxidizing and reducing conditions during SG 009 formation may be connected with a chemical microenvironment and possibly could indicate that G chondrites may have formed by a planetesimal collision resulting in the lack of matrix.

The dust never settles: collisional production of gas and dust in evolved planetary systems

ABSTRACT Multi-epoch infrared photometry from Spitzer is used to monitor circumstellar discs at white dwarfs, which are consistent with disrupted minor planets whose debris is accreted and chemically reflected by their host stars. Widespread infrared variability is found across the population of 37 stars with two or more epochs. Larger flux changes occur on longer time-scales, reaching several tens of per cent over baselines of a few years. The canonical model of a geometrically thin, optically thick disc is thus insufficient, as it cannot give rise to the observed behaviour. Optically thin dust best accounts for the variability, where collisions drive dust production and destruction. Notably, the highest infrared variations are seen in systems that show Ca ii emission, supporting planetesimal collisions for all known debris discs, with the most energetic occurring in those with detected gaseous debris. The sample includes the only polluted white dwarf with a circumbinary disc, where the signal of the day–night cycle of its irradiated substellar companion appears diluted by dust emission.

Evolution of α Centauri b’s protoplanetary disc

ABSTRACT With hydrodynamical simulations we examine the evolution of a protoplanetary disc around α Centauri B including the effect of the eccentric orbit binary companion α Centauri A. The initially circular orbit disc undergoes two types of eccentricity growth. First, the eccentricity oscillates on the orbital period of the binary, Porb, due to the eccentricity of the binary orbit. Secondly, for a sufficiently small disc aspect ratio, the disc undergoes global forced eccentricity oscillations on a time-scale of around $20\, P_{\rm orb}$. These oscillations damp out through viscous dissipation leaving a quasi-steady eccentricity profile for the disc that oscillates only on the binary orbital period. The time-averaged global eccentricity is in the range 0.05–0.1, with no precession in the steady state. The periastrons of the gas particles are aligned to one another. The higher the disc viscosity, the higher the disc eccentricity. With N-body simulations we examine the evolution of a disc of planetesimals that forms with the orbital properties of the quasi-steady protoplanetary disc. We find that the average magnitude of the eccentricity of particles increases and their periastrons become misaligned to each other once they decouple from the gas disc. The low planetesimal collision velocity required for planet formation suggests that for planet formation to have occurred in a disc of planetesimals formed from a protoplanetary disc around α Centauri B, said disc’s viscosity must be have been small and planet formation must have occurred at orbital radii smaller than about $2.5\, \rm au$. Planet formation may be easier with the presence of gas.

New HST data and modeling reveal a massive planetesimal collision around Fomalhaut

The apparent detection of an exoplanet orbiting Fomalhaut was announced in 2008. However, subsequent observations of Fomalhaut b raised questions about its status: Unlike other exoplanets, it is bright in the optical and nondetected in the infrared, and its orbit appears to cross the debris ring around the star without the expected gravitational perturbations. We revisit previously published data and analyze additional Hubble Space Telescope (HST) data, finding that the source is likely on a radial trajectory and has faded and become extended. Dynamical and collisional modeling of a recently produced dust cloud yields results consistent with the observations. Fomalhaut b appears to be a directly imaged catastrophic collision between two large planetesimals in an extrasolar planetary system. Similar events should be very rare in quiescent planetary systems of the age of Fomalhaut, suggesting that we are possibly witnessing the effects of gravitational stirring due to the orbital evolution of hypothetical planet(s) around the star.

Realistic collisional water transport during terrestrial planet formation

Context. According to the latest theoretical and isotopic evidence, Earth’s water content originates mainly from today’s asteroid belt region, or at least from the same precursor material. This suggests that water was transported inwards to Earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation. Aims. In current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. To close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term N-body computations with dedicated 3D smooth particle hydrodynamics (SPH) collision simulations of differentiated, self-gravitating bodies for each event. Methods. Post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. This hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred Myr). As a first application we choose a Solar System-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5–4 au). Results. Including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. Due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more Earth-like values, and closer to results with eccentric giant planets. Water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. The high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general.

The Properties of Planetesimal Collisions under Jupiter’s Perturbation and the Application to Chondrule Formation via Impact Jetting

Abstract Understanding chondrule formation provides invaluable clues about the origin of the solar system. Recent studies suggest that planetesimal collisions and the resulting impact melts are promising for forming chondrules. Given that the dynamics of planetesimals is a key in impact-based chondrule formation scenarios, we here perform direct N-body simulations to examine how the presence of Jupiter affects the properties of chondrule-forming collisions. Our results show that the absence/presence of Jupiter considerably changes the properties of high-velocity collisions whose impact velocities are higher than 2.5 km s−1. High-velocity collisions occur due to impacts between protoplanets and planetesimals for the case without Jupiter; for the case with Jupiter, the eccentricities of planetesimals are pumped up by the secular and resonant perturbations from Jupiter. We also categorize the resulting planetesimal collisions and find that most high-velocity collisions are classified as grazing ones for both cases. To examine the effect of Jupiter on chondrule formation directly, we adopt the impact-jetting scenario and compute the resulting abundance of chondrules. Our results show that for the case without Jupiter, chondrule formation proceeds in the inside-out manner, following the growth of protoplanets. If Jupiter is present, the location and timing of chondrule formation are determined by Jupiter’s eccentricity, which is treated as a free parameter in our simulations. Thus, the existence of Jupiter is the key parameter for specifying when and where chondrule formation occurs for impact-based scenarios.

Constraining the detectability of water ice in debris disks

Context.Water ice is important for the evolution and preservation of life. Identifying the distribution of water ice in debris disks is therefore of great interest in the field of astrobiology. Furthermore, icy dust grains are expected to play important roles throughout the entire planet formation process. However, currently available observations only allow deriving weak conclusions about the existence of water ice in debris disks.Aims.We investigate whether it is feasible to detect water ice in typical debris disk systems. We take the following ice destruction mechanisms into account: sublimation of ice, dust production through planetesimal collisions, and photosputtering by UV-bright central stars. We consider icy dust mixture particles with various shapes consisting of amorphous ice, crystalline ice, astrosilicate, and vacuum inclusions (i.e., porous ice grains).Methods.We calculated optical properties of inhomogeneous icy dust mixtures using effective medium theories, that is, Maxwell-Garnett rules. Subsequently, we generated synthetic debris disk observables, such as spectral energy distributions and spatially resolved thermal reemission and scattered light intensity and polarization maps with our code DMS.Results.We find that the prominent ~3 and 44μm water ice features can be potentially detected in future observations of debris disks with theJames WebbSpace Telescope (JWST) and the Space Infrared telescope for Cosmology and Astrophysics (SPICA). We show that the sublimation of ice, collisions between planetesimals, and photosputtering caused by UV sources clearly affect the observational appearance of debris disk systems. In addition, highly porous ice (or ice-rich aggregates) tends to produce highly polarized radiation at around 3μm. Finally, the location of the ice survival line is determined by various dust properties such as a fractional ratio of ice versus dust, physical states of ice (amorphous or crystalline), and the porosity of icy grains.

Linking planetesimal and dust content in protoplanetary disks via a local toy model

Context. If planetesimal formation is an efficient process, as suggested by several models involving gravitational collapse of pebble clouds, then, not before long, a significant part of the primordial dust mass should be absorbed in many km-sized objects. A good understanding of the total amount of solids in the disk around a young star is crucial for planet formation theory. However, as the mass of particles above the mm size cannot be assessed observationally, one must ask how much mass is hidden in bigger objects. Aims. We performed 0-d local simulations to study how the planetesimal to dust and pebble ratio evolves in time and to develop an understanding of the potentially existing mass in planetesimals for a certain amount of dust and pebbles at a given disk age. Methods. We performed a parameter study based on a model considering dust growth, planetesimal formation, and collisional fragmentation of planetesimals, while neglecting radial transport processes. Results. While at early times, dust is the dominant solid particle species, there is a phase during which planetesimals make up a significant portion of the total mass starting at approximately 104–106 yr. The time of this phase and the maximal total planetesimal mass strongly depend on the distance to the star R, the initial disk mass, and the efficiency of planetesimal formation ɛ. Planetesimal collisions are more significant in more massive disks, leading to lower relative planetesimal fractions compared to less massive disks. After approximately 106 yr, our model predicts planetesimal collisions to dominate, which resupplies small particles. Conclusions. In our model, planetesimals form fast and everywhere in the disk. For a given ɛ, we are able to relate the dust content and mass of a given disk to its planetesimal content, providing us with some helpful basic intuition about mass distribution of solids and its dependence on underlying physical processes.

Probabilities of Collisions of Planetesimals from Different Regions of the Feeding Zone of the Terrestrial Planets with the Forming Planets and the Moon

Migration of planetesimals from the feeding zone of the terrestrial planets, which was divided into seven regions depending on the distance to the Sun, was simulated. The influence of gravity of all planets was taken into account. In some cases, the embryos of the terrestrial planets rather than the planets themselves were considered; their masses were assumed to be 0.1 or 0.3 of the current masses of the planets. The arrays of orbital elements of migrated planetesimals were used to calculate the probabilities of their collisions with the planets, the Moon, or their embryos. Based on our calculations, we drew conclusions on the process of accumulation of the terrestrial planets. The embryos of the terrestrial planets, the masses of which did not exceed a tenth of the current planetary masses, accumulated planetesimals mainly from the vicinity of their orbits. When planetesimals fell onto the embryos of the terrestrial planets from the feeding zone of Jupiter and Saturn, these embryos had not yet acquired the current masses of the planets, and the material of this zone (including water and volatiles) could be accumulated in the inner layers of the terrestrial planets. The inner layers of each of the terrestrial planets were mainly formed from the material located in the vicinity of the orbit of a certain planet. The outer layers of the Earth and Venus could accumulate the same material for these two planets from different parts of the feeding zone of the terrestrial planets. The Earth and Venus could acquire more than half of their masses in 5 Myr. A relatively rapid growth of the bulk of the Martian mass can be explained by the formation of Mars' embryo (the mass of which is several times less than that of Mars) due to contraction of a rarefied condensation.