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Determining how and when Mars formed has been a long-standing challenge for planetary scientists. The size and orbit of Mars are difficult to reproduce in classical simulations of planetary accretion, and this has inspired models of inner solar system evolution that are tuned to produce Mars-like planets. However, such models are not always coupled to geochemical constraints. Analyses of Martian meteorites using the extinct hafnium–tungsten (Hf–W) radioisotopic system, which is sensitive to the timing of core formation, have indicated that the Martian core formed within a few million years of the start of the solar system itself. This has been interpreted to suggest that, unlike Earth’s protracted accretion, Mars grew to its modern size very rapidly. These arguments, however, generally rely on simplified growth histories for Mars. Here, we combine likely accretionary histories from a large number of N-body simulations with calculations of metal–silicate partitioning and Hf–W isotopic evolution during core formation to constrain the range of conditions that could have produced Mars. We find that there is no strong correlation between the final masses or orbits of simulated Martian analogs and their 182W anomalies, and that it is readily possible to produce Mars-like Hf–W isotopic compositions for a variety of accretionary conditions. The Hf–W signature of Mars is very sensitive to the oxygen fugacity (fO2) of accreted material because the metal–silicate partitioning behavior of W is strongly dependent on redox conditions. The average fO2 of Martian building blocks must fall in the range of 1.3–1.6 log units below the iron–wüstite buffer to produce a Martian mantle with the observed Hf/W ratio. Other geochemical properties (such as sulfur content) also influence Martian 182W signatures, but the timing of accretion is a more important control. We find that while Mars must have accreted most of its mass within ~5 million years of solar system formation to reproduce the Hf–W isotopic constraints, it may have continued growing afterwards for over 50 million years. There is a high probability of simultaneously matching the orbit, mass, and Hf–W signature of Mars even in cases of prolonged accretion if giant impactor cores were poorly equilibrated and merged directly with the proto-Martian core.

Amorphous silicates in meteoritic samples are significant as potential surviving interstellar dust from the formation of the Solar System. Amorphous silicate-rich grains called GEMS, glass with embedded metal and sulfides, are abundant in anhydrous interplanetary dust particles and some ultracarbonaceous Antarctic micrometeorites that have high presolar grain abundances. Some GEMS within these objects have been confirmed to be presolar. GEMS-like material, consisting of amorphous silicate with opaque inclusions, has been identified in the matrices of some primitive meteorites. We use specialized thin specimen preparation and transmission electron microscopy methods to compare the GEMS-like material in Paris (CM) and Acfer 094 (ungrouped) chondrites with GEMS in anhydrous, chondritic interplanetary dust particles. Specifically, we compared the amorphous silicate morphology, degree of partial ordering, elemental composition and dominant iron oxidation state. We find that the amorphous silicates in the GEMS-like materials in Paris and Acfer 094 show incipient ordering and are Fe-rich and highly oxidized, while those in GEMS are fully amorphous, Fe-poor, and anhydrous. From examination of various formation routes for the amorphous silicates, we conclude that the GEMS-like material in Paris and Acfer 094 is not GEMS and that it is unlikely that GEMS-like material accreted as primary amorphous material that retained its original amorphous structure since accretion. We also conclude that the presence of GEMS-like amorphous silicates in chondrite matrix is not a reliable indicator for high degrees of primitivity or pristinity since even mild, complex alteration processes may significantly alter silicate structure. Finally, we propose searches for presolar amorphous silicates in chondrite matrix samples that have been precharacterized by transmission electron microscopy methods to enable direct comparisons of presolar amorphous silicate abundances.

Anomalies among the daughter nuclei of the extinct short-lived radionuclides (SLRs) in the calcium-aluminum-rich inclusions (CAIs) indicate that the Solar System must have been born near a source of the SLRs so that they could be incorporated before they decayed away. $\gamma$-rays from one such living SLR, $^{26}$Al, are detected in only a few nearby star-forming regions. Here we employ multi-wavelength observations to demonstrate that one such region, Ophiuchus, containing many pre-stellar cores that may serve as analogs for the emerging Solar System, is inundated with $^{26}$Al from the neighboring Upper-Scorpius association, and so may provide concrete guidance for how SLR enrichment proceeded in the Solar System complementary to the meteoritics. We demonstrate via Bayesian forward modeling drawing on a wide range of observational and theoretical results that this $^{26}$Al likely 1) arises from supernova explosions, 2) arises from multiple stars, 3) has enriched the gas prior to the formation of the cores, and 4) gives rise to a broad distribution of core enrichment spanning about two orders of magnitude. This means that if the spread in CAI ages is small, as it is in the Solar System, protoplanetary disks must suffer a global heating event., Comment: Published in Nature Astronomy, August 16, 2021

In this work, we propose a novel campaign for constraining relativistically compact massive compact halo object (MACHO) dark matter, such as primordial black holes (PBHs), using the Moon as a detector. PBHs of about 1019 to 1022 g may be sufficiently abundant to have collided with the Moon in the history of the Solar system. We show that the crater profiles of a PBH collision differ from traditional impactors and may be detectable in high-resolution lunar surface scans now available. Any candidates may serve as sites for in situ measurements to identify high-pressure phases of matter which may have formed near the PBH during the encounter. While we primarily consider PBH dark matter, the discussion generalizes to the entire family of MACHO candidates with relativistic compactness. Moreover, we focus on the Moon since it has been studied well, but the same principles can be applied to other rocky bodies in our Solar system without an atmosphere.

The developed Hypersphere World-Universe Model (WUM) is consistent with all Concepts of the World [1]. In WUM, we postulate the principal role of Angular Momentum and Dark Matter in Cosmological theories of the World. The most widely accepted model of Solar System formation, known as the Nebular hypothesis, does not solve the Angular Momentum problem—why is the orbital momentum of Jupiter larger than rotational momentum of the Sun? WUM is the only cosmological model in existence that is consistent with this Fundamental Law. The Nebular hypothesis does not solve Internal Heating and Diversity problems for all Planets and Moons in Solar system—why the actual mean surface temperature of them is higher than their effective temperature calculated based on the Sun’s heat for them and how could each one be so different if all of them came from the same nebula? The proposed concept of Dark Matter Reactors in Cores of all gravitationally-rounded Macroobjects successfully resolves these problems.

The formation of the solar system's terrestrial planets concluded with a period of giant impacts. Previous works examining the volatile loss caused by the impact shock in the moon-forming impact find atmospheric losses of at most 20-30 per cent and essentially no loss of oceans. However, giant impacts also result in thermal heating, which can lead to significant atmospheric escape via a Parker-type wind. Here we show that H2O and other high-mean molecular weight outgassed species can be efficiently lost through this thermal wind if present in a hydrogen-dominated atmosphere, substantially altering the final volatile inventory of terrestrial planets. Specifically, we demonstrate that a giant impact of a Mars-sized embryo with a proto-Earth can remove several Earth oceans' worth of H2O, and other heavier volatile species, together with a primordial hydrogen-dominated atmosphere. These results may offer an explanation for the observed depletion in Earth's light noble gas budget and for its depleted xenon inventory, which suggest that Earth underwent significant atmospheric loss by the end of its accretion. Because planetary embryos are massive enough to accrete primordial hydrogen envelopes and because giant impacts are stochastic and occur concurrently with other early atmospheric evolutionary processes, our results suggest a wide diversity in terrestrial planet volatile budgets., Comment: submitted to MNRAS, 9 pages, 4 figures

Timing Solar System formation The oldest solids that formed in the Solar System are calcium-aluminium–rich inclusions (CAIs), small metallic droplets that were later incorporated into meteorites. The ages of CAIs are conventionally taken as the age of the Solar System, but which exact moment in star formation they correspond to has been unclear. Brennecka et al. measured molybdenum isotope ratios in CAIs and found a wide range of origins in both the inner and outer Solar System. They propose that CAIs formed from heterogeneous material accreting from the presolar nebula and that the ages of CAIs coincide with the Sun's transition from a protostar to a pre–main sequence star. Science , this issue p. 837

Two ancient asteroids with distinctive diamond-like shapes are revealing clues not only about their own formation, but that of the solar system as well. For the past three years, two spacecraft have been studying a pair of the most primitive solar system objects ever explored. The asteroids, Ryugu and Bennu, born of violent collisions in the asteroid belt, are some of the smallest objects ever visited by spacecraft. Ryugu is just over a kilometer across, and Bennu is about half as wide. The asteroid Bennu ejects particles from its surface in January 2019—a phenomenon captured in an image composed from multiple photos. Image credit: NASA/Goddard/University of Arizona/Lockheed Martin. But these small bodies are promising a huge bounty of data to astronomers over the next few years. Although the findings could revolutionize our understanding of the history, formation, and composition of asteroids, they may also tell us a little about the solar system during its infancy. That’s because these carbon-rich (1) asteroids, with their coal-dark surfaces, are also among the darkest bodies known in the solar system. Although that can make it difficult to observe them from Earth, studying them could tell us about the building blocks of life that such asteroids may have delivered to Earth early in the history of the solar system. Before researchers could hope to study these asteroids, they first had to reach them. This, by itself, was an enormous challenge. Only a handful of spacecraft have visited asteroids, and fewer still have managed to orbit one of these tiny, irregularly shaped objects. The Hayabusa spacecraft, launched by the Japanese Aerospace Exploration Agency (JAXA) in 2003, became the first to collect a sample of an asteroid. But the mission was beset by engine problems. Hayabusa’s prospects for returning with a sample remained uncertain for much of …

Calcium–aluminium-rich inclusions (CAIs) are one of the first solids to have condensed in the solar nebula, while presolar grains formed in various evolved stellar environments. It is generally accepted that CAIs formed close to the Sun at temperatures above 1,500 K, where presolar grains could not survive, and were then transported to other regions of the nebula where the accretion of planetesimals took place. In this context, a commonly held view is that presolar grains are found solely in the fine-grained rims surrounding chondrules and in the low-temperature fine-grained matrix that binds the various meteoritic components together. Here we demonstrate, on the basis of noble gas isotopic signatures, that presolar SiC grains were incorporated into fine-grained CAIs in the Allende carbonaceous chondrite at the time of their formation, and have survived parent-body processing. This finding provides new clues on the conditions in the nascent Solar System at the condensation of the first solids.

The isotopic composition of meteorites and terrestrial planets holds important clues about the earliest history of the Solar System and the processes of planet formation. Recent work has shown that meteorites exhibit a fundamental isotopic dichotomy between non-carbonaceous (NC) and carbonaceous (CC) groups, which most likely represent material from the inner and outer Solar System, respectively. Here we review the isotopic evidence for this NC–CC dichotomy, discuss its origin and highlight the far-reaching implications for the dynamics of the solar protoplanetary disk. The NC–CC dichotomy combined with the chronology of meteorite parent-body accretion mandate an early and prolonged spatial separation of inner (NC) and outer (CC) disk reservoirs, lasting between ~1 and ~4 Myr after Solar System formation. This is most easily reconciled with the early and rapid growth of Jupiter’s core, inhibiting substantial exchange of material from inside and outside its orbit. The growth and migration of Jupiter also led to the later implantation of CC bodies into the inner Solar System and, therefore, can explain the co-occurrence of NC and CC bodies in the asteroid belt, and the delivery of volatile and water-rich CC bodies to the terrestrial planets. Cosmochemical measurements reveal the existence of two distinct reservoirs of non-carbonaceous and carbonaceous materials, originating from the inner and outer protoplanetary disk, respectively, which separated after the first million years after the birth of the Solar System, possibly due to the rapid growth of Jupiter’s core.

Missions to asteroids are now an important component of the space exploration program of major space agencies in the world, with the goal of better understanding the formation of the Solar system and learn about their dynamics to be able to react in case of a possible collision with the Earth. As binary asteroids compose approximately 16% of near Earth asteroids, they are getting more attention from researchers. One mission is currently being planned to binary asteroid system 65803 Didymos. This mission motivates research on the dynamics of a spacecraft near a binary asteroid. Since the primary bodies of these binary systems have small masses, perturbations like the Solar Radiation Pressure (SRP) or the shape of the primary bodies have a great influence on the dynamics of a spacecraft in their vicinity. Studies that already exist on the effect of the SRP on the dynamics of a spacecraft near binary asteroid systems have mostly used low-fidelity SRP acceleration models, such as the cannonball model or simple flat plate model with a purely reflecting spacecraft. This study shows how the choice of the model influences the strength of the SRP acceleration acting on the spacecraft and how it is possible to take advantage of the choice of the nominal attitude of the spacecraft to influence how the SRP affects the spacecraft dynamics when using a more complex SRP acceleration model. Various types of trajectories are studied, with different results and conclusions.

Type 3 chondritic meteorites often contain chondrules and refractory inclusions that are coated with accretionary, fine-grained rims (FGRs). FGRs are of low porosity, were subject to centrally directed pressure, may contain high temperature products like microchondrules and there is a linear relationship between the rim thickness and the radius of the enclosed object. FGRs are thought to have formed by the gentle adhesion of dust onto the central object with the subsequent compression of this fluffy rim within the parent body. However, this model does not explain the low porosity, micro-chondrules and centralized pressure. This model also has difficulties explaining the linear relationship between rim thickness and object size including the existence of a non-zero constant in that linear relationship. We propose that FGRs formed by the relatively high-speed interaction between dust and the object, where high initial impact speed produced abrasion and, possibly, microchondrules. FGR formation occurred over a range of lower speeds aided by vacuum adhesion of fragments from the impacting dust particles. This model naturally produces the rim thickness linear relationship with non-zero constant, low porosity and centrally directed pressure. We call this process kinetic dust aggregation (KDA), which is another name for the aerosol deposition processes used in industry. KDA may be a tentative, part explanation of how dust aggregation occurs in protostellar disks on the pathway from dust to planets., 34 pages, 7 figures

We present new nucleosynthetic, radiogenic and stable Sr isotopic data from fifteen previously studied CAIs from the Allende CV3 meteorite, including the highly altered Curious Marie inclusion. We use double-spike TIMS techniques to determine the degrees of isotopic mass fractionation, and also present internally normalised data for the same sample digestions to permit comparisons with previous studies and couple these isotopic data with Rb, Sr, Eu and Th abundance data to consider the origins and relationships of the isotopic variations documented here. Analysed CAIs display elevated μ^(84)Sr anomalies of +58 ppm to +287 ppm, with variability far outside of analytical uncertainties (13 ppm 2 s.d.). We cannot tell at present whether these variations arise from heterogeneities in p-process ^(84)Sr or in the other non-radiogenic isotopes of Sr (^(86)Sr, ^(88)Sr) that are produced by the main s-process, weak s-process, and r-process. All inclusions fall on an offset mass-dependent fractionation line in three-isotope space (δ^(88/86)Sr vs δ^(84/86)Sr) identical within error to that previously defined by bulk undifferentiated meteorites, and have a total range of δ^(88/86)Sr of ∼5.3 ‰ (+1.67 ‰ to -3.67 ‰), reflecting kinetic isotope effects during partial condensation/evaporation and/or low-temperature alteration processes. CI-normalized Sr/Th ratios in our CAIs correlate with normalized Eu/Th ratios with a ∼1:1 relationship, regardless of texture or Sr-isotopic values. This indicates that Sr and Eu had similar condensation behaviors with Eu condensing as Eu^(2+) and having the same chemical behavior in minerals as Sr^(2+) under conditions relevant to CAI formation in the solar nebula. Rb/Th ratios are highly variable: fine-grained CAIs display elevated Rb/Th ratios, consistent with the introduction of Rb into the CAIs by alkali-rich secondary alteration fluids. The μ ^(84)Sr anomalies measured in our CAIs are similar (in magnitude) to those found in carbonaceous chondrites that formed in the outer part of the solar system. A way to reconcile this observation with the formation of CAIs near the Sun would be if the inventories of Sr and other refractory elements in carbonaceous chondrites are dominated by a cryptic refractory dust component (CRD) that was formed early and near the Sun, and was subsequently transported outwards to the carbonaceous chondrite-forming region.

Stars grow by accreting gas that has an evolving composition owing to the growth and inward drift of dust (pebble wave), the formation of planetesimals and planets, and the selective removal of hydrogen and helium by disk winds. We investigated how the formation of the Solar System may have affected the composition and structure of the Sun, and whether it plays any role in solving the solar abundance problem. We simulated the evolution of the Sun from the protostellar phase to the present age and attempted to reproduce spectroscopic and helioseismic constraints. We performed chi-squared tests to optimize our input parameters. We confirmed that, for realistic models, planet formation occurs when the solar convective zone is still massive; thus, the overall changes due to planet formation are too small to significantly improve the chi-square fits. We found that solar models with up-to-date abundances require an opacity increase of 12% to 18% centered at $T=10^{6.4}$ K to reproduce the available observational constraints. This is slightly higher than, but is qualitatively in good agreement with, recent measurements of higher iron opacities. These models result in better fits to the observations than those using old abundances; therefore, they are a promising solution to the solar abundance problem. Using these improved models, we found that planet formation processes leave a small imprint in the solar core, whose metallicity is enhanced by up to 5%. This result can be tested by accurately measuring the solar neutrino flux. In the improved models, the protosolar molecular cloud core is characterized by a primordial metallicity in the range 0.0127-0.0157 and a helium mass fraction in the range 0.268-0.274. (abridged), Accepted for publication in A&A. 24 pages, 17 figures

The ungrouped iron meteorite Nedagolla is the first meteorite with bulk Mo, Ru, and Ni isotopic compositions that are intermediate between those of the non-carbonaceous (NC) and carbonaceous (CC) meteorite reservoirs. The Hf-W chronology of Nedagolla indicates that this mixed NC-CC isotopic composition was established relatively late, more than 7 million years after Solar System formation. The mixed NC-CC isotopic composition is consistent with the chemical composition of Nedagolla, which combines signatures of metal segregation under more oxidizing conditions (relative depletions in Mo and W), characteristic for CC bodies, and more reducing conditions (high Si and Cr contents), characteristic for some NC bodies, in a single sample. These data combined suggest that Nedagolla formed as the result of collisional mixing of NC and CC core material, which partially re-equilibrated with silicate mantle material that predominantly derives from the NC body. These mixing processes might have occurred during a hit-and-run collision between two differentiated bodies, which also provides a possible pathway for Nedagolla's extreme volatile element depletion. As such, Nedagolla provides the first isotopic evidence for early collisional mixing of NC and CC bodies that is expected as a result of Jupiter's growth., Accepted for publication in Meteoritics & Planetary Science

Description, Paleomagnetic measurements of chondrules indicate the presence of a substructure in the solar nebula., Astronomical observations and isotopic measurements of meteorites suggest that substructures are common in protoplanetary disks and may even have existed in the solar nebula. Here, we conduct paleomagnetic measurements of chondrules in CO carbonaceous chondrites to investigate the existence and nature of these disk substructures. We show that the paleomagnetism of chondrules in CO carbonaceous chondrites indicates the presence of a 101 ± 48 μT field in the solar nebula in the outer solar system (~3 to 7 AU from the Sun). The high intensity of this field relative to that inferred from inner solar system (~

Using the multi-band imager MapCam onboard the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft, we identified 77 instances of proposed exogenic materials distributed globally on the surface of the B-type asteroid (101955) Bennu. We identified materials as exogenic on the basis of an absorption near 1 um that is indicative of anhydrous silicates. The exogenic materials are spatially resolved by the telescopic camera PolyCam. All such materials are brighter than their surroundings, and they are expressed in a variety of morphologies: homogeneous, breccia-like, inclusion-like, and others. Inclusion-like features are the most common. Visible spectrophotometry was obtained for 46 of the 77 locations from MapCam images. Principal component analysis indicates at least two trends: (i) mixing of Bennu's average spectrum with a strong 1-um band absorption, possibly from pyroxene-rich material, and (ii) mixing with a weak 1-um band absorption. The endmember with a strong 1-um feature is consistent with Howardite-Eucrite-Diogenite (HED) meteorites, whereas the one showing a weak 1-um feature may be consistent with HEDs, ordinary chondrites, or carbonaceous chondrites. The variation in the few available near-infrared reflectance spectra strongly suggests varying compositions among the exogenic materials. Thus, Bennu might record the remnants of multiple impacts with different compositions to its parent body, which could have happened in the very early history of the Solar System. Moreover, at least one of the exogenic objects is compositionally different from the exogenic materials found on the similar asteroid (162173) Ryugu, and they suggest different impact tracks., 39 pages, 19 figures, accepted manuscript for MNRAS

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We describe the AMBITION project, a mission to return the first-ever cryogenically-stored sample of a cometary nucleus, that has been proposed for the ESA Science Programme Voyage 2050. Comets are the leftover building blocks of giant planet cores and other planetary bodies, and fingerprints of Solar System’s formation processes. We summarise some of the most important questions still open in cometary science and Solar System formation after the successful Rosetta mission. We show that many of these scientific questions require sample analysis using techniques that are only possible in laboratories on Earth. We summarize measurements, instrumentation and mission scenarios that can address these questions. We emphasize the need for returning a sample collected at depth or, still more challenging, at cryogenic temperatures while preserving the stratigraphy of the comet nucleus surface layers. We provide requirements for the next generation of landers, for cryogenic sample acquisition and storage during the return to Earth. Rendezvous missions to the main belt comets and Centaurs, expanding our knowledge by exploring new classes of comets, are also discussed. The AMBITION project is discussed in the international context of comet and asteroid space exploration.

International audience; Heterogeneity in isotopic compositions within the protoplanetary disc has been demonstrated for a number of elements measured in extra-terrestrial materials, mostly based on chondrite meteorite analyses. However, precise 182Hf-182W and 26Al-26Mg ages of iron meteorites, achondrites, and chondrules show that chondrites accreted later than achondrites and therefore do not strictly represent the early (145Nd/144Nd and 148Nd/144Nd ratios (3.9 145Nd < 11.0 and 9.1 148Nd < 17.9 in part per million deviation, or μiNd) compared to NC chondrites (2.7 145Nd < 3.3 and 2.2 148Nd < 8.1). Moreover, the three terrestrial planets for which we have samples available (Earth, Mars, and the Moon) as well as the silicate inclusions from the non-magmatic IIE iron meteorite Miles present a systematic deficit in μ145Nd and μ148Nd compared to early-formed NC achondrites. Unlike chondrites, the Nd anomalies in achondrites are not correlated to the heliocentric distance of accretion of their respective parent bodies as inferred from redox conditions. Chronological constraints on planetesimal accretion suggest that Nd (and other elements such as Mo and Zr) nucleosynthetic compositions of the inner part of the protoplanetary disc significantly changed around 1.5 Ma after Solar System formation due to thermal processing of dust in the protoplanetary disc. This relatively late event coincides with the beginning of chondrule formation or at least their preservation. Terrestrial planets formed subsequently by a complex accretion regime during several million years. Therefore, two scenarios are envisioned considering the reported Nd isotope composition of early planetesimals: 1) Terrestrial planets accreted mostly chondritic material similar in composition to enstatite chondrites, or 2) early planetesimals constitute substantial parts of terrestrial planets building blocks mixed with highly thermally processed material enriched in s-process, still unsampled by meteorites.

Dynamical scenarios of terrestrial planets formation involve strong perturbations of the inner part of the solar system by the giant-planets, leading to enhanced impact velocities and subsequent collisional erosion. We quantitatively estimate the effect of collisional erosion on the resulting composition of Earth, and estimate how it may provide information on the dynamical context of its formation. We simulate and quantify the erosion of Earth's crust in the context of Solar System formation scenarios, including the classical model and Grand Tack scenario that invokes orbital migration of Jupiter during the gaseous disk phase (Walsh et al., 2011; Raymond et al., 2018). We find that collisional erosion of the early crust is unlikely to produce an excess of about 6% of the Sm/Nd ratio in terrestrial rock samples compared to chondrites for most simulations. Only Grand Tack simulations in which the last giant impact on Earth occurred later than 50 million years after the start of Solar System formation can account for such an offset. However, this time frame is consistent with current cosmochemical and dynamical estimates of the Moon forming impact (Chyba, 1991; Walker, 2009; Touboul et al.,2007, 2009, 2015; Pepin and Porcelli, 2006; Norman et al., 2003; Nyquist et al., 2006; Boyet et al.,2015). Such a late fractionation in the Sm/Nd ratio is unlikely to be responsible for a 20-ppm $^{142}$Nd excess in terrestrial rocks due to the half life of the radiogenic system. Additionally, such a large and late fractionation in the Sm/Nd ratio would accordingly induce non-observed anomalies in the $^{143}$Nd/$^{144}$Nd ratio. Considering our results, the Grand Tack model with a late Moon-forming impact cannot be easily reconciled with the Nd isotopic Earth contents., 22 pages, 3 figures, supplementary, to be published

The formation of the solar system's giant planets predated the ultimate epoch of massive impacts that concluded the process of terrestrial planet formation. Following their formation, the giant planets' orbits evolved through an episode of dynamical instability. Several qualities of the solar system have recently been interpreted as evidence of this event transpiring within the first ~100 Myr after the Sun's birth; around the same time as the final assembly of the inner planets. In a series of recent papers we argued that such an early instability could resolve several problems revealed in classic numerical studies of terrestrial planet formation; namely the small masses of Mars and the asteroid belt. In this paper, we revisit the early instability scenario with a large suite of simulations specifically designed to understand the degree to which Earth and Mars' formation are sensitive to the specific evolution of Jupiter and Saturn's orbits. By deriving our initial terrestrial disks directly from recent high-resolution simulations of planetesimal accretion, our results largely confirm our previous findings regarding the instability's efficiency of truncating the terrestrial disk outside of the Earth-forming region in simulations that best replicate the outer solar system. Moreover, our work validates the primordial 2:1 Jupiter-Saturn resonance within the early instability framework as a viable evolutionary path for the solar system. While our simulations elucidate the fragility of the terrestrial system during the epoch of giant planet migration, many realizations yield outstanding solar system analogs when scrutinized against a number of observational constraints. Finally, we highlight the inability of models to form adequate Mercury-analogs and the low eccentricities of Earth and Venus as the most significant outstanding problems for future numerical studies to resolve., 24 pages, 10 figures, 6 tables, accepted for publication in Icarus

Planets grow via the collisional accretion of small bodies in a protoplanetary disk. Such small bodies feel strong gas drag and their orbits are significantly affected by the gas flow and atmospheric structure around the planet. We investigate the gas flow in the protoplanetary disk perturbed by the gravity of the planet by three-dimensional hydrodynamic simulation. We then calculate the orbital evolutions of particles in the gas structure obtained from the hydrodynamic simulation. Based on the orbital calculations, we obtain the collision rate between the planet and centimeter to kilometer sized particles. Our results show that meter-sized or larger particles effectively collide with the planet due to the atmospheric gas drag, which significantly enhances the collision rate. On the other hand, the gas flow plays an important role for smaller particles. Finally, considering the effects of the atmosphere and gas flow, we derive the new analytic formula for the collision rate, which is in good agreement with our simulations. We estimate the growth timescale and accretion efficiency of drifting bodies for the formation of a gas-giant solid core using the formula. We find the accretion of sub-kilometer sized bodies achieve a short growth timescale (~0.005 Myr) and a high accretion efficiency (~1) for the core formation at 5 au in the minimum mass solar nebula model., Accepted for publication in The Astrophysical Journal

We present a chronology of the formation and early evolution of the Oort cloud by simulations. These simulations start with the Solar System being born with planets and asteroids in a stellar cluster orbiting the Galactic center. Upon ejection from its birth environment, we continue to follow the evolution of the Solar System while it navigates the Galaxy as an isolated planetary system. We conclude that the range in semi-major axis between 100au and several 10$^3$\,au still bears the signatures of the Sun being born in a 1000MSun/pc$^3$ star cluster, and that most of the outer Oort cloud formed after the Solar System was ejected. The ejection of the Solar System, we argue, happened between 20Myr and 50Myr after its birth. Trailing and leading trails of asteroids and comets along the Sun's orbit in the Galactic potential are the by-product of the formation of the Oort cloud. These arms are composed of material that became unbound from the Solar System when the Oort cloud formed. Today, the bulk of the material in the Oort cloud ($\sim 70$\%) originates from the region in the circumstellar disk that was located between $\sim 15$\,au and $\sim 35$\,au, near the current location of the ice giants and the Centaur family of asteroids. According to our simulations, this population is eradicated if the ice-giant planets are born in orbital resonance. Planet migration or chaotic orbital reorganization occurring while the Solar System is still a cluster member is, according to our model, inconsistent with the presence of the Oort cloud. About half the inner Oort cloud, between 100 and $10^4$\,au, and a quarter of the material in the outer Oort cloud, $\apgt 10^4$\,au, could be non-native to the Solar System but was captured from free-floating debris in the cluster or from the circumstellar disk of other stars in the birth cluster., Corrected proofs for publication in A&A

Following the recent detection of HCl in the atmosphere of Mars by ExoMars/Trace Gas Orbiter, we present here the first measurement of the 37Cl/35Cl isotopic ratio in the Martian atmosphere using a set of Nadir Occultation for MArs Discovery (NOMAD) observations. We determine an isotopic anomaly of −6 ± 78‰ compared to Earth standard, consistent with the −51‰–−1‰ measured on Mars’ surface by Curiosity. The measured isotopic ratio is also consistent with surface measurements, and suggests that Cl reservoirs may have undergone limited processing since formation in the Solar Nebula. The examination of possible sources and sinks of HCl shows only limited pathways to short-term efficient Cl fractionation and many plausible reservoirs of “light” Cl. © 2021. American Geophysical Union., ExoMars is a space mission of the European Space Agency (ESA) and Roscosmos. The NOMAD experiment is led by the Royal Belgian Institute for Space Aeronomy (IASB-BIRA), assisted by Co-PI teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University). This project acknowledges funding by the Belgian Science Policy Office (BELSPO), with the financial and contractual coordination by the ESA Prodex Office (PEA 4000103401, 4000121493), by the Spanish MICINN through its Plan Nacional and by European funds under grants PGC2018-101836-B-I00 and ESP2017-87143-R (MINECO/FEDER), as well as by UK Space Agency through grants ST/V002295/1, ST/V005332/1 and ST/S00145X/1 and Italian Space Agency through grant 2018-2-HH.0. The IAA/CSIC team acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award for the Instituto de Astrofisica de Andalucia (SEV-2017-0709), and the CBK PAN team from the EXOMHYDR project, carried out within the TEAM program of the Foundation for Polish Science cofinanced by the European Union under the European Regional Development Fund (TEAM/2016-3/20). This work was supported by NASA's Mars Program Office under WBS 604796, "Participation in the TGO/NOMAD Investigation of Trace Gases on Mars" and by NASA's SEEC initiative under Grant Number NNX17AH81A, "Remote sensing of Planetary Atmospheres in the Solar System and Beyond." U.S. investigators were supported by the National Aeronautics and Space Administration. S. Viscardy acknowledges support from the Belgian Fonds de la Recherche Scientifique-FNRS under grant numbers 30442502 (ET_HOME) and Belgian Science Policy Office BrainBe MICROBE Projects. S. Aoki is "Charge de Recherches" at the F.R.S-FNRS. F. Schmidt acknowledges support from the "Institut National des Sciences de l'Univers" (INSU), the "Center National de la Recherche Scientifique" (CNRS) and "Center National d'Etudes Spatiales" (CNES) through the "Program National de Planetologie". S. Robert thanks BELSPO for the FED-tWIN funding (Prf-2019-077-RT-MOLEXO).

Noble gases are important tracers of planetary accretion and acquisition of volatiles to planetary atmospheres and interiors. Earth’s mantle hosts solar-type helium and neon for which 20Ne/22Ne ratios advocate either incorporation of solar wind irradiated solids or solar nebula gas dissolution into an early magma ocean. However, the exact source location of primordial signatures remains unclear. Here we use high-resolution stepwise heating gas extraction experiments to analyse interior samples of the iron meteorite Washington County and find that they contain striking excesses of solar helium and neon. We infer that the Washington County protolith was irradiated by solar wind and that implanted noble gases were partitioned into segregating metal melts. The corollary that solar signatures are able to enter the cores of differentiated planetesimals and protoplanets validates hypotheses that Earth’s core may have incorporated solar noble gases and may be contributing to the solar signatures observed in Earth’s mantle. Incorporation of iron meteorites in the core could explain variable noble gas signatures in different mantle reservoirs, according to stepwise heating experiments which show that the Washington County meteorite carries solar wind-derived He and Ne.

We develop empirical relationships for the accretion and erosion of colliding gravity-dominated bodies of various compositions under conditions expected in late-stage solar system formation. These are fast, easily coded relationships based on a large database of smoothed particle hydrodynamics (SPH) simulations of collisions between bodies of different compositions, including those that are water rich. The accuracy of these relations is also comparable to the deviations of results between different SPH codes and initial thermal/rotational conditions. We illustrate the paucity of disruptive collisions between major bodies, as compared to collisions between less massive planetesimals in late-stage planet formation, and thus focus on more probable, low-velocity collisions, though our relations remain relevant to disruptive collisions as well. We also pay particular attention to the transition zone between merging collisions and those where the impactor does not merge with the target, but continues downrange, a “hit-and-run” collision. We find that hit-and-run collisions likely occur more often in density-stratified bodies and across a wider range of impact angles than suggested by the most commonly used analytic approximation. We also identify a possible transitional zone in gravity-dominated collisions where larger bodies may undergo more disruptive collisions when the impact velocity exceeds the sound speed, though understanding this transition warrants further study. Our results are contrary to the commonly assumed invariance of total mass (scale), density structure, and material composition on the largest remnants of giant impacts. We provide an algorithm for adopting our model into N-body planet formation simulations, so that the mass of growing planets and debris can be tracked.

The evolutionary system of mineralogy relies on varied physical and chemical attributes, including trace elements, isotopes, solid and fluid inclusions, and other information-rich characteristics, to understand processes of mineral formation and to place natural condensed phases in the deep-time context of planetary evolution. Part I of this system reviewed the earliest refractory phases that condense at T > 1000 K within the turbulent expanding and cooling atmospheres of highly evolved stars. Part II considers the subsequent formation of primary crystalline and amorphous phases by condensation in three distinct mineral-forming environments, each of which increased mineralogical diversity and distribution prior to the accretion of planetesimals >4.5 billion years ago. (1). INTERSTELLAR MOLECULAR SOLIDS: Varied crystalline and amorphous molecular solids containing primarily H, C, O, and N are observed to condense in cold, dense molecular clouds in the interstellar medium (10 < T < 20 K; P < 10(−13) atm). With the possible exception of some nanoscale organic condensates preserved in carbonaceous meteorites, the existence of these phases is documented primarily by telescopic observations of absorption and emission spectra of interstellar molecules in radio, microwave, or infrared wavelengths. (2). NEBULAR AND CIRCUMSTELLAR ICE: Evidence from infrared observations and laboratory experiments suggest that cubic H(2)O (“cubic ice”) condenses as thin crystalline mantles on oxide and silicate dust grains in cool, distant nebular and circumstellar regions where T ~100 K. (3). PRIMARY CONDENSED PHASES OF THE INNER SOLAR NEBULA: The earliest phase of nebular mineralogy saw the formation of primary refractory minerals that solidified through high-temperature condensation (1100 < T < 1800 K; 10(−6) < P < 10(−2) atm) in the solar nebula more than 4.565 billion years ago. These earliest mineral phases originating in our solar system formed prior to the accretion of planetesimals and are preserved in calcium-aluminum-rich inclusions, ultra-refractory inclusions, and amoeboid olivine aggregates.

We propose that chondrules and chondrites formed together during a brief radiative heating event caused by the close encounter of a small (m to km-scale), primitive planetesimal (SPP) with incandescent lava on the surface of a large (100 km-scale) differentiated planetesimal (LDP). In our scenario, chondrite lithification occurs by hot isostatic pressing (HIP) simultaneously with chondrule formation, in accordance with the constraints of complementarity and cluster chondrites. Thermal models of LDPs formed near t=0 predict that there will be a very narrow window of time, coincident with the chondrule formation epoch, during which crusts are thin enough to frequently rupture by impact, volcanism and/or crustal foundering, releasing hot magma to their surfaces. The heating curves we calculate are more gradual and symmetric than the "flash heating" characteristic of nebular models, but in agreement with the constraints of experimental petrology. The SPP itself is a plausible source of the excess O, Na and Si vapor pressure (compared to a solar nebula environment) that is required by chondrule observations. Laboratory experiments demonstrate that FeO-poor porphyritic olivine chondrules, the most voluminous type of chondrule, can be made using heating and cooling curves predicted by the "flyby" model. If chondrules are a by-product of chondrite lithification, then their high volume abundance within well-lithified chondritic material is not evidence that they were once widespread within the Solar System. Relatively rare events, such as the flybys modeled here, could account for their abundance in the meteorite record., Accepted for publication in Icarus

著者人数: 50名, 資料番号: SA1190102000

Chromium isotopic data of physically separated components (chondrules, CAIs, variably magnetic size fractions) of the carbonaceous chondrites Allende and Murchison and bulk rock data of Allende, Ivuna, and Orgueil are reported to evaluate the origin of isotopic heterogeneity in these meteorites. Allende components show ε53Cr and ε54Cr from −0.23 ± 0.07 to 0.37 ± 0.05 and from −0.43 ± 0.08 to 3.7 ± 0.1, respectively. In components of Murchison, ε53Cr and ε54Cr vary from −0.06 ± 0.08 to 0.5 ± 0.1 and from 0.7 ± 0.2 to 1.7 ± 0.1, respectively. The non‐systematic variations of ε53Cr and 55Mn/52Cr in the components of Allende and Murchison were likely caused by small‐scale, alteration‐related redistribution of Mn >20 Ma after formation of the solar system. Chondrule fractions show the lowest 55Mn/52Cr and ε54Cr values of all components, consistent with evaporation of Mn and ε54Cr‐rich carrier phases from chondrule precursors. Components other than the chondrules show higher Mn/Cr and ε54Cr, suggestive of chemical and isotopic complementarity between chondrules and matrix‐rich fractions. Bulk rock compositions calculated based on weighted compositions of components agree with measured Cr isotope data of bulk rocks, in spite of the Cr isotopic heterogeneity reported by the present and previous studies. This indicates that on a sampling scale comprising several hundred milligrams, these meteorites sampled isotopically and chemically homogeneous nebular reservoirs. The linear correlation of 55Mn/52Cr with ε53Cr in bulk rocks likely was caused by variable fractionation of Mn/Cr, subsequent mixing of phases in nebular domains, and radiogenic ingrowth of 53Cr., DFG‐SPP 1385 http://dx.doi.org/10.13039/501100001659

The textures and accretion ages of chondrites have been used to argue that their parent asteroids never differentiated. Without a core, undifferentiated planetesimals could not have generated magnetic fields through dynamo activity, so chondrites are not expected to have experienced such fields. However, the magnetic remanence carried by the CV chondrites is consistent with dynamo-generated fields, hinting that partially differentiated asteroids consisting of an unmelted crust atop a differentiated interior may exist. Here, we test this hypothesis by applying synchrotron X-ray microscopy to metallic veins in the slowly cooled H6 chondrite Portales Valley. The magnetic remanence carried by nanostructures in these veins indicates that this meteorite recorded a magnetic field over a period of tens to hundreds of years at ∼100 Myr after solar system formation. These properties are inconsistent with external field sources such as the nebula, solar wind, or impacts, but are consistent with dynamo-generated fields, indicating that the H chondrite parent body contained an advecting metallic core and was therefore partially differentiated. We calculate the thermal evolution of the chondritic portions of partially differentiated asteroids that form through incremental accretion across 105 to 106 years, finding this can agree with the measured ages and cooling rates of multiple H chondrites. We also predict that the cores of these bodies could have been partially liquid and feasibly generating a dynamo at 100 Myr after solar system formation. These observations contribute to a growing body of evidence supporting a spectrum of internal differentiation within some asteroids with primitive surfaces., NASA Solar System Exploration Research Virtual Institute (Grant NNA14AB01A), NASA Solar System Workings Program (Grant NNX15AL62G), Thomas F. Peterson, Jr., Office of Science, Office of Basic Energy Sciences of the U.S. D.O.E. (Contract DE-AC02-05CH11231)

Studies of internal structure of gas giant planets suggest that their envelopes are enriched with heavier elements than hydrogen and helium relative to their central stars. Such enrichment likely occurred by solid accretion during late formation stages of gas giant planets in which gas accretion dominates protoplanetary growth. Some previous studies performed orbital integration of planetesimals around a growing protoplanet with the assumption of an uniform circumstellar disc to investigate how efficiently the protoplanet captures planetesimals. However, not only planetesimals but also disc gas are gravitationally perturbed by the protoplanet in its late formation stages, resulting in gap opening in the circumstellar disc. In this study, we investigate the effects of such gap formation on the capture of planetesimals by performing dynamical simulations of planetesimals around a growing proto-gas giant planet. Gap formation reduces the surface density of disc gas, makes a steep pressure gradient and limits the growth rate of the protoplanet. We find that the first effect enhances the capture of planetesimals, while the others reduce it. Consequently the amount of planetesimals captured during the gas accretion is estimated to be at most ~3 Mearth. We conclude that the in-situ capture of planetesimals needs the initial solid surface density more than five times higher than that of the minimum mass solar nebula for explaining the inferred large amount of heavy element in Jupiter. For highly dense warm Jupiters, we would need additional processes enhancing the capture and/or supply of planetesimals., Comment: 15 pages, 13 figures, this is a pre-copyedited, author-produced version of an article accepted for publication in MNRAS following peer review

A growing body of evidence indicates that binary neutron-star mergers are the primary origin of heavy elements produced exclusively through rapid neutron capture1-4 (the 'r-process'). As neutron-star mergers occur infrequently, their deposition of radioactive isotopes into the pre-solar nebula could have been dominated by a few nearby events. Although short-lived r-process isotopes-with half-lives shorter than 100 million years-are no longer present in the Solar System, their abundances in the early Solar System are known because their daughter products were preserved in high-temperature condensates found in meteorites5. Here we report that abundances of short-lived r-process isotopes in the early Solar System point to their origin in neutron-star mergers, and indicate substantial deposition by a single nearby merger event. By comparing numerical simulations with the early Solar System abundance ratios of actinides produced exclusively through the r-process, we constrain the rate of occurrence of their Galactic production sites to within about 1-100 per million years. This is consistent with observational estimates of neutron-star merger rates6-8, but rules out supernovae and stellar sources. We further find that there was probably a single nearby merger that produced much of the curium and a substantial fraction of the plutonium present in the early Solar System. Such an event may have occurred about 300 parsecs away from the pre-solar nebula, approximately 80 million years before the formation of the Solar System.

In order to characterize the early growth of fine-grained dust rims (FGRs) that commonly surround chondrules, we perform numerical simulations of dust accretion onto chondrule surfaces. We employ a Monte Carlo algorithm to simulate the collision of dust monomers having radii between 0.5 and 10 $\mu$m with chondrules whose radii are between 500 and 1000 $\mu$m, in 100-$\mu$m increments. The collisions are driven by Brownian motion and solar nebula turbulence. After each collision, the colliding particles either stick at the point of contact, roll or bounce. We limit accretion of dust monomers (and in some cases, dust aggregates) to a small patch of the chondrule surface, for computational expediency. We model the morphology of the dust rim and the trajectory of the dust particle, which are not considered in most of the previous works. Radial profiles of FGR porosity show that rims formed in weak turbulence are more porous (with a porosity of 60-74\%) than rims formed in stronger turbulence (with a porosity of 52-60\%). The lower end of each range corresponds to large chondrules and the upper end to small chondrules, meaning that the chondrule size also has an impact on FGR porosity. The thickness of FGRs depends linearly on chondrule radius, and the slope of this linear dependency increases with time, and decreases with the turbulence strength. The porosity of FGRs formed by dust aggregates is $\sim 20\%$ on average greater than that of FGRs formed by single monomers. In general, the relatively high porosities that we obtain are consistent with those calculated by previous authors from numerical simulations, as well as with initial FGR porosities inferred from laboratory measurements of rimmed chondrule samples and rimmed chondrule analogs., Comment: 25 pages, 22 figures

著者人数: 13名, Accepted: 2019-01-22, 資料番号: SA1180366000

We explore in situ formation and subsequent evolution of close-in super-Earths and mini-Neptunes. We adopt a steady-state inner protoplanetary gas disc structure that arises from viscous accretion due to the magneto-rotational instability (MRI). We consider the evolution of dust in the inner disc, including growth, radial drift and fragmentation, and find that dust particles that radially drift into the inner disc fragment severely due to the MRI-induced turbulence. This result has two consequences: (1) radial drift of grains within the inner disc is quenched, leading to an enhancement of dust in the inner regions which scales as dust-to-gas-mass-flux-ratio at ~1 AU; (2) however, despite this enhancement, planetesimal formation is impeded by the small grain size. Nevertheless, assuming that planetary cores are present in the inner disc, we then investigate the accretion of atmospheres onto cores and their subsequent photoevaporation. We then compare our results to the observed exoplanet mass-radius relationship. We find that: (1) the low gas surface densities and high temperatures in the inner disc reduce gas accretion onto cores compared to the minimum mass solar nebula, preventing the cores from growing into hot Jupiters, in agreement with the data; (2) however, our predicted envelope masses are still typically larger than observed ones. Finally, we sketch a qualitative picture of how grains may grow and planetesimals form in the inner disc if grain effects on the ionization levels and the MRI and the back-reaction of the dust on the gas (both neglected in our calculations) are accounted for., Comment: Accepted for publication in MNRAS

Impacts on undifferentiated asteroidal bodies provide invaluable information for understanding the solar system evolution. Nevertheless, dating early and small-scale impact events is technically challenging. Uranium-lead (U-Pb) systematics of U-bearing phases within shock-induced melt veins (SMVs) of chondrites may be significantly disturbed by localized heating, thus providing opportunities to date these impact events. As one of the major U hosts in chondrites, apatite in the Suizhou (L6) chondrite has been compositionally and structurally modified to varying degrees by shock metamorphism. Apatite grains in the host remained largely intact during the impact and have recorded the initial thermal cooling time (similar to 4550 Ma) on their parent body. Apatite grains in regions less than 100 mu m bordering the SMVs or in relatively "cold" regions within the SMVs were partly decomposed to tuite, driven by the localized transient heating within the SMVs. Their U-Pb systematics were disrupted to varying extents. Apatite in regions close to the center of the SMVs has been completely transformed to tuite, which yields an age of 4481 +/- 30 Ma (2 sigma), providing an upper limit to the impact event. This study clearly demonstrates that by integrating in situ U-Pb isotope analysis with detailed microstructural and compositional analysis of phosphates, it is possible to deduce the timing of early and small-scale celestial impact events, and hence create a more comprehensive understanding of the impact history of the solar system.

The proposed US Extremely Large Telescope (ELT) Program would secure national open access to at least 25% of the observing time on the Thirty Meter Telescope in the north and the Giant Magellan Telescope in the south. ELTs would advance solar system science via exceptional angular resolution, sensitivity, and advanced instrumentation. ELT contributions would include the study of interstellar objects, giant planet systems and ocean worlds, the formation of the solar system traced through small objects in the asteroid and Kuiper belts, and the active support of planetary missions. We recommend that (1) the US ELT Program be listed as critical infrastructure for solar system science, that (2) some support from NASA be provided to ensure mission support capabilities, and that (3) the US ELT Program expand solar-system community participation in development, planning, and operations.

Geochemical and astronomical evidence demonstrate that planet formation occurred in two spatially and temporally separated reservoirs. The origin of this dichotomy is unknown. We use numerical models to investigate how the evolution of the solar protoplanetary disk influenced the timing of protoplanet formation and their internal evolution. Migration of the water snow line can generate two distinct bursts of planetesimal formation that sample different source regions. These reservoirs evolve in divergent geophysical modes and develop distinct volatile contents, consistent with constraints from accretion chronology, thermo-chemistry, and the mass divergence of inner and outer Solar System. Our simulations suggest that the compositional fractionation and isotopic dichotomy of the Solar System was initiated by the interplay between disk dynamics, heterogeneous accretion, and internal evolution of forming protoplanets., Comment: Published 21 January 2021; authors' version; 30 pages, 18 figures; summary available at http://bit.ly/BifurcationBlog (blog) and https://bit.ly/BifurcationVideo (video)

Calcium-aluminum-rich inclusions (CAIs) are the first solids to form in the early Solar System, and they exhibit nucleosynthetic anomalies in many isotope systems. The overwhelming majority of isotopic data for CAIs has been limited to inclusions from the CV chondrite Allende and a select few other CV, CO, CM, and ordinary chondrites. It is therefore important to ascertain whether previously reported values for CAIs are representative of the broader CAI-forming region and to make a more rigorous assessment of the extent and implications of isotopic heterogeneity in the early Solar System. Here, we report the mass-independent Ti isotopic compositions of a suite of 23 CAIs of diverse petrologic and geochemical types, including 11 from Allende and 12 from seven other CV3 and CK3 chondrites; the data for CAIs from CK chondrites represent the first reported measurements of Ti isotope compositions of refractory inclusions from this meteorite class. The resolved variation in the mass-independent Ti isotopic compositions of these CAIs indicates that the CAI-forming region of the early Solar System preserved isotopic variability at their time of formation. Nevertheless, the range of Ti isotope compositions reported here for CAIs from CV and CK chondrites falls within the range observed in previously analyzed CAIs from CV, CO, CM, and ordinary chondrites. This implies that CAIs from CV, CK, CO, CM, and ordinary chondrites originated from a common nebular source reservoir characterized by mass-independent isotopic variability in Ti (and other select elements). We further interpret these data to indicate that the Ti isotope anomalies in CAIs represent the isotopic signatures of supernova components in presolar grains that were incorporated into the Solar System in an initially poorly mixed reservoir that was progressively homogenized over time. We conclude that the differing degrees of isotopic variability observed for different elements in normal CAIs are the result of distinct carrier phases and that these CAIs were likely formed towards the final stages of homogenization of the large-scale isotopic heterogeneity that initially existed in the solar nebula.

The compositions of the first solar system solids were shaped by nonequilibrium condensation and evaporation., Equilibrium condensation of solar gas is often invoked to explain the abundance of refractory elements in planets and meteorites. This is partly motivated, by the observation that the depletions in both the least and most refractory rare earth elements (REEs) in meteoritic group II calcium-aluminum–rich inclusions (CAIs) can be reproduced by thermodynamic models of solar nebula condensation. We measured the isotopic compositions of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb in eight CAIs to test this scenario. Contrary to expectation for equilibrium condensation, we find light isotope enrichment for the most refractory REEs and more subdued isotopic variations for the least refractory REEs. This suggests that group II CAIs formed by a two-stage process involving fast evaporation of preexisting materials, followed by near-equilibrium recondensation. The calculated time scales are consistent with heating in events akin to FU Orionis– or EX Lupi–type outbursts of eruptive pre–main-sequence stars.

[abridged] Measurements of relative isotope abundances can provide unique insights into the formation and evolution histories of celestial bodies. The five stable isotopes of titanium are used to study the early history of the solar system and constrain Galactic chemical models. The minor isotopes of titanium are relatively abundant compared to those of other elements, making them more accessible for challenging observations. We assessed the feasibility of performing titanium isotope measurements in exoplanet atmospheres, and in particular, whether processing techniques used for high-resolution spectroscopy affect the derived isotope ratios. We used an archival high-dispersion CARMENES spectrum of the M-dwarf GJ 1002 as a proxy for an exoplanet observed at very high signal-to-noise. Spectral retrievals using petitRADTRANS models were performed on both narrow (7045-7090 {\AA}) and wide (7045-7500 {\AA}) wavelength regions, resulting in isotope ratios and uncertainties. These retrievals were repeated on the spectrum with its continuum removed to mimic typical high-dispersion exoplanet observations. The relative abundances of all minor Ti isotopes are found to be slightly enhanced compared to terrestrial values. Loss of continuum information from broadband spectral filtering has little effect on the isotope ratios. The CARMENES spectrum was subsequently degraded by adding varying levels of Gaussian noise to estimate the signal-to-noise requirements for future exoplanet atmospheric observations. For the wide wavelength range, a spectrum with signal-to-noise of 5 is required to determine the isotope ratios with relative errors $\lesssim$10%. Super Jupiters at large angular separations from their host star are the most accessible exoplanets, requiring about an hour of observing time on 8-meter-class telescopes, and less than a minute of observing time with the future Extremely Large Telescope., Comment: Accepted to A&A; 13 pages, 6 figures

The inner solar system possesses a unique orbital structure in which there are no planets inside the Mercury orbit and the mass is concentrated around the Venus and Earth orbits. The origins of these features still remain unclear. We propose a novel concept that the building blocks of the inner solar system formed at the dead-zone inner edge in the early phase of the protosolar disk evolution, where the disk is effectively heated by the disk accretion. First, we compute the dust evolution in a gas disk with a dead zone and obtain the spatial distribution of rocky planetesimals. The disk is allowed to evolve both by a viscous diffusion and magnetically-driven winds. We find that the rocky planetesimals are formed in concentrations around $\sim$ 1 au with a total mass comparable to the mass of the current inner solar system in the early phase of the disk evolution within $\lesssim0.1$ Myr. Based on the planetesimal distribution and the gas disk structure, we subsequently perform \textit{N}-body simulations of protoplanets to investigate the dynamical configuration of the planetary system. We find that the protoplanets can grow into planets without significant orbital migration because of the rapid clearing of the inner disk by the magnetically-driven disk winds. Our model can explain the origins of the orbital structure of the inner solar system. Several other features such as the rocky composition can also be explained by the early formation of rocky planetesimals., Comment: 8 pages, 6 figures, accepted for publication in ApJL

Compared to the composition of CI chondrites and the Sun, all other carbonaceous chondrites are variably depleted in volatile elements. However, the origin of these depletions, and how they are related to volatile loss during high-temperature processes within the solar nebula, are unclear. To better understand the processes that caused volatile element fractionations among carbonaceous chondrites, we obtained mass-dependent Te isotopic compositions and Te concentrations for a comprehensive set of samples from the major carbonaceous chondrite groups. The chondrites exhibit well-resolved inter-group Te isotope variations towards lighter isotopic compositions for increasingly volatile-depleted samples. The Te isotopic compositions and concentrations are also correlated with the mass fraction of matrix and with nucleosynthetic e 54 Cr anomalies. Combined, these correlations indicate mixing between volatile-rich, isotopically heavy, and 54Cr-rich CI-like matrix with volatile-poor, isotopically light, and 54Cr-poorer chondrules or chondrule precursors. The Te-Cr isotopic correlation suggests that all carbonaceous chondrites contain CI-like matrix, and that chondrules and this CI-like matrix formed from isotopically distinct material originating from different regions of the disk. The only samples plotting off the Te-Cr correlation are CR chondrites, indicating that CR chondrules formed from different precursor material than chondrules from other carbonaceous chondrites, either because they formed at greater heliocentric distance and/or at a later time. Plots of volatile element abundances versus matrix mass fraction reveal that chondrules/chondrule precursors display CI-chondritic ratios for volatile elements with 50% condensation temperatures below ∼750 K, with an overall abundance of ∼0.13 × CI. Mixing between these two components, therefore, naturally results in CI-like ratios for these elements in all carbonaceous chondrites, in spite of different degrees of volatile depletion. A corollary of this observation is that the CI-like ratios of volatile elements in the bulk silicate Earth may result from the accretion of volatile-depleted materials and do not require accretion of CI chondrites themselves.

Context.Asteroid families are witnesses to the intense collisional evolution that occurred on the asteroid belt. The study of the physical properties of family members can provide important information about the state of differentiation of the parent body and provide insights into how these objects were formed. Several of these asteroid families identified across the main belt are dominated by low-albedo, primitive asteroids. These objects are important for the study of Solar System formation because they were subject to weaker thermophysical processing and provide information about the early conditions of our planetary system.Aims.We aim to study the diversity of physical properties among the Themis, Hygiea, Ursula, Veritas, and Lixiaohua families.Methods.We present new spectroscopic data, combined with a comprehensive analysis using a variety of data available in the literature, such as albedo and rotational properties.Results.Our results show that Themis and Hygiea families, the largest families in the region, present similar levels of hydration. Ursula and Lixiaohua families are redder in comparison to the others and present no sign of hydrated members based on the analysis of visible spectra. Conversely, Veritas presents the highest fraction of hydrated members.Conclusions.This work demonstrates a diverse scenario in terms of the physical properties of primitive outer-belt families, which could be associated with dynamical mixing of asteroid populations and the level of differentiation of the parental body.

Recent observations of the long-period comet C/2016 R2 (PanSTARRS; hereafter R2) indicate an unusually high N2/CO abundance ratio, typically larger than ∼0.05, and at least 2–3 times higher than the one measured in 67P/Churyumov–Gerasimenko. Another striking compositional feature of this comet is its heavy depletion in H2O (H2O/CO ∼ 0.32%), compared to other comets. Here we investigate the formation circumstances of a generic comet whose composition reproduces these two key features. We first envisage the possibility that this comet agglomerated from clathrates, but we find that such a scenario does not explain the observed low water abundance. We then alternatively investigate the possibility that the building blocks of R2 agglomerated from grains and pebbles made of pure condensates via the use of a disk model describing the radial transport of volatiles. We show that N2/CO ratios reproducing the value estimated in this comet can be found in grains condensed in the vicinity of the CO and N2 ice lines. Moreover, high CO/H2O ratios (>100 times the initial gas-phase value) can be found in grains condensed in the vicinity of the CO ice line. If the building blocks of a comet assembled from such grains, they should present N2/CO and CO/H2O ratios consistent with the measurements made in R2’s coma. Our scenario indicates that R2 formed in a colder environment than the other comets that share more usual compositions. Our model also explains the unusual composition of the interstellar comet 2l/Borisov.