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The mass-independent calcium isotope composition of inner-Solar-System bodies is correlated with their masses and accretion ages, indicating a rapid growth for the precursors of Earth and the Moon during the protoplanetary disk’s lifetime. Like Earth, like moon Variation in the isotopic composition of material within the early inner Solar System is usually thought to reflect spatial heterogeneity in the protoplanetary disk. Martin Schiller and co-authors find that the calcium isotope composition of samples from the parent bodies of ureilite and angrite meteorites, as well as from Vesta, Mars and Earth, are correlated to the masses of their inferred parent asteroids and planets. This provides a proxy for their accretion timescales and implies a rapid 'secular' evolution of the bulk calcium isotope composition of the disk in the rocky-planet-forming region. The authors infer that this secular evolution reflects the introduction of pristine outer-Solar-System material to the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. They also conclude that the indistinguishable calcium isotope composition of the Earth and the Moon implies that the Moon-forming impact involved protoplanets that completed their accretion near the end of the disk's lifetime. Nucleosynthetic isotope variability among Solar System objects is often used to probe the genetic relationship between meteorite groups and the rocky planets (Mercury, Venus, Earth and Mars), which, in turn, may provide insights into the building blocks of the Earth–Moon system 1 , 2 , 3 , 4 , 5 . Using this approach, it has been inferred that no primitive meteorite matches the terrestrial composition and the protoplanetary disk material from which Earth and the Moon accreted is therefore largely unconstrained 6 . This conclusion, however, is based on the assumption that the observed nucleosynthetic variability of inner-Solar-System objects predominantly reflects spatial heterogeneity. Here we use the isotopic composition of the refractory element calcium to show that the nucleosynthetic variability in the inner Solar System primarily reflects a rapid change in the mass-independent calcium isotope composition of protoplanetary disk solids associated with early mass accretion to the proto-Sun. We measure the mass-independent 48 Ca/ 44 Ca ratios of samples originating from the parent bodies of ureilite and angrite meteorites, as well as from Vesta, Mars and Earth, and find that they are positively correlated with the masses of their parent asteroids and planets, which are a proxy of their accretion timescales. This correlation implies a secular evolution of the bulk calcium isotope composition of the protoplanetary disk in the terrestrial planet-forming region. Individual chondrules from ordinary chondrites formed within one million years of the collapse of the proto-Sun 7 reveal the full range of inner-Solar-System mass-independent 48 Ca/ 44 Ca ratios, indicating a rapid change in the composition of the material of the protoplanetary disk. We infer that this secular evolution reflects admixing of pristine outer-Solar-System material into the thermally processed inner protoplanetary disk associated with the accretion of mass to the proto-Sun. The identical calcium isotope composition of Earth and the Moon reported here is a prediction of our model if the Moon-forming impact involved protoplanets or precursors that completed their accretion near the end of the protoplanetary disk’s lifetime.

Volatiles are vital ingredients for a habitable planet. Angrite meteorites sample the most volatile-depleted planetesimal in the Solar System, particularly for the alkali elements. They are prime targets for investigating the formation of volatile-poor rocky planets, yet their exceptionally low volatile content presents a major analytical challenge. Here, we leverage improved sensitivity and precision of K isotopic analysis to constrain the mechanism of extreme K depletion (>99.8%) in angrites. In contrast with the isotopically heavy Moon and Vesta, we find that angrites are strikingly depleted in the heavier K isotopes, which is best explained by partial recondensation of vaporized K following extensive evaporation on the angrite parent body (APB) during magma-ocean stage. Therefore, the APB may provide a rare example of isotope fractionation controlled by condensation, rather than evaporation, at a planetary scale. Furthermore, nebula-wide K isotopic variations primarily reflect volatility-driven fractionations instead of presolar nucleosynthetic heterogeneity proposed previously. This study reports strikingly light K isotopic compositions for the extremely K-depleted angrite meteorites, thereby providing the first observation of isotope fractionation likely controlled by partial recondensation at a planetary scale.

Understanding the nature and origin of the precursor material to terrestrial planets is key to deciphering the mechanisms and timescales of planet formation 1 . Nucleosynthetic variability among rocky Solar System bodies can trace the composition of planetary building blocks 2 – 5 . Here we report the nucleosynthetic composition of silicon (μ 30 Si), the most abundant refractory planet-building element, in primitive and differentiated meteorites to identify terrestrial planet precursors. Inner Solar System differentiated bodies, including Mars, record μ 30 Si deficits of −11.0 ± 3.2 parts per million to −5.8 ± 3.0 parts per million whereas non-carbonaceous and carbonaceous chondrites show μ 30 Si excesses from 7.4 ± 4.3 parts per million to 32.8 ± 2.0 parts per million relative to Earth. This establishes that chondritic bodies are not planetary building blocks. Rather, material akin to early-formed differentiated asteroids must represent a major planetary constituent. The μ 30 Si values of asteroidal bodies correlate with their accretion ages, reflecting progressive admixing of a μ 30 Si-rich outer Solar System material to an initially μ 30 Si-poor inner disk. Mars’ formation before chondrite parent bodies is necessary to avoid incorporation of μ 30 Si-rich material. In contrast, Earth’s μ 30 Si composition necessitates admixing of 26 ± 9 per cent of μ 30 Si-rich outer Solar System material to its precursors. The μ 30 Si compositions of Mars and proto-Earth are consistent with their rapid formation by collisional growth and pebble accretion less than three million years after Solar System formation. Finally, Earth’s nucleosynthetic composition for s -process sensitive (molybdenum and zirconium) and siderophile (nickel) tracers are consistent with pebble accretion when volatility-driven processes during accretion and the Moon-forming impact are carefully evaluated. The nucleosynthetic composition of silicon in meteorites indicates that material akin to early-formed differentiated asteroids must represent a major constituent of terrestrial planets such as Earth and Mars.

Analysis of the metallicities of more than 400 stars hosting 600 candidate extrasolar planets shows that the planets can be categorized by size into three populations — terrestrial-like planets, gas dwarf planets with rocky cores and hydrogen–helium envelopes, and ice or gas giant planets — on the basis of host star metallicity. Three regimes of exoplanet radius arising from host star metallicities Soon after the discovery of the first exoplanets, it was suggested that host star metallicity — the abundance of elements other than hydrogen and helium — has a role in the formation of planetary systems. Here Lars Buchhave et al . report the metallicity and other stellar parameters of more than 400 stars hosting 600 exoplanet candidates and find that the exoplanets can be categorized into three populations defined by statistically distinct metallicity regions and planetary radii. The three are terrestrial-like exoplanets, gas dwarf exoplanets with rocky cores and H/He envelopes, and ice/gas-giant exoplanets. Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods 1 . Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (∼4.5 σ ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen–helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates 2 , 3 , implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.

H2 in a CO2 atmosphere may serve as a potential solution to the early Mars climate paradox, but its unknown sources cast doubts on the proposed mechanism. Impact cratering is an energetic process that may modify the surface redox budget. Here, we investigate the potential influence of impact‐related melt oxidation and serpentinization on global climate conditions. We show that impact melt and the projectile's significant oxidizing potential during basin‐forming impacts (Basin size ≥1,250 km) result in sufficient H2 to raise the global mean temperature to above 273K, which lasts for up to 105 − 106 yr considering rate‐limited regime. Impact‐induced serpentinization has limited consequences on the global climate in comparison. Episodic warming after large impacts may have enabled the presence of liquid water for up to several million years in the Noachian, resulting in the chemical evolution of the planet's surface co‐evolving with the planetary atmosphere in an episodic manner. Plain Language Summary It remains debated how early Mars maintained a climate allowing for the presence of widespread ancient rivers, lakes, and water‐bearing minerals. Recent work proposed that hydrogen mixed with a CO2 atmosphere has a greenhouse warming effect, but such a model requires a significant amount of these gases. The known sources, for example, volcanic degassing, are insufficient to sustain the required abundance. Alternatively, impact cratering provides enormous energy that mixes the wet sedimentary rock on the surface with a reduced crust and mantle. In this study, we calculate the potential influence of impact‐induced oxidation on changing global climate on early Mars. We show that impact melt oxidation can immediately increase hydrogen abundances in the martian atmosphere and contribute to warming early Mars for several million years. Thus episodic warming may have occurred due to impact oxidation during the formation of large impact basins on early Mars. The impact‐related processes suggest that the warming of early Mars due to reduced gasses remains a valid hypothesis. Our study also indicates that the red planet's oxidized surface may be a by‐product of its early bombardment history. Key Points Oxidation of melt sheets in large impact basins has a significant effect on the warm early Mars Rate‐limiting processes could have extended the timescale of melt oxidation H2–CO2 atmosphere remains a working hypothesis to resolve the early Mars conundrum

Transient heating events that formed calcium-aluminum-rich inclusions (CAIs) and chondrules are fundamental processes in the evolution of the solar protoplanetary disk, but their chronology is not understood. Using U-corrected Pb-Pb dating, we determined absolute ages of individual CAIs and chondrules from primitive meteorites. CAIs define a brief formation interval corresponding to an age of 4567.30 ± 0.16 million years (My), whereas chondrule ages range from 4567.32 ± 0.42 to 4564.71 ± 0.30 My. These data refute the long-held view of an age gap between CAIs and chondrules and, instead, indicate that chondrule formation started contemporaneously with CAIs and lasted ~3 My. This time scale is similar to disk lifetimes inferred from astronomical observations, suggesting that the formation of CAIs and chondrules reflects a process intrinsically linked to the secular evolution of accretionary disks.

The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of infalling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

Earth’s mantle has a two-layered structure, with the upper and lower mantle domains separated by a seismic discontinuity at about 660 km (refs.  1 , 2 ). The extent of mass transfer between these mantle domains throughout Earth’s history is, however, poorly understood. Continental crust extraction results in Ti-stable isotopic fractionation, producing isotopically light melting residues 3 – 7 . Mantle recycling of these components can impart Ti isotope variability that is trackable in deep time. We report ultrahigh-precision 49 Ti/ 47 Ti ratios for chondrites, ancient terrestrial mantle-derived lavas ranging from 3.8 to 2.0 billion years ago (Ga) and modern ocean island basalts (OIBs). Our new Ti bulk silicate Earth (BSE) estimate based on chondrites is 0.052 ± 0.006‰ heavier than the modern upper mantle sampled by normal mid-ocean ridge basalts (N-MORBs). The 49 Ti/ 47 Ti ratio of Earth’s upper mantle was chondritic before 3.5 Ga and evolved to a N-MORB-like composition between approximately 3.5 and 2.7 Ga, establishing that more continental crust was extracted during this epoch. The +0.052 ± 0.006‰ offset between BSE and N-MORBs requires that <30% of Earth’s mantle equilibrated with recycled crustal material, implying limited mass exchange between the upper and lower mantle and, therefore, preservation of a primordial lower-mantle reservoir for most of Earth’s geologic history. Modern OIBs record variable 49 Ti/ 47 Ti ratios ranging from chondritic to N-MORBs compositions, indicating continuing disruption of Earth’s primordial mantle. Thus, modern-style plate tectonics with high mass transfer between the upper and lower mantle only represents a recent feature of Earth’s history. Titanium isotope measurements for chondrites, ancient terrestrial mantle-derived lavas and modern ocean island basalts imply the preservation of a primordial lower-mantle reservoir for most of Earth’s geologic history.

Planetary materials show systematic variations in their nucleosynthetic isotope compositions that resonate with orbital distance. The origin of this pattern remains debated, limiting how these isotopic signatures can be used to trace the precursors of terrestrial planets. Here we test the hypothesis that interstellar ices carried supernova-produced nuclides by searching for a supernova nucleosynthetic fingerprint in aqueous alteration minerals from carbonaceous and non-carbonaceous chondrite meteorites. We focus on zirconium, a refractory element that includes the neutron-rich isotope 96 Zr formed in core-collapse supernovae. Leaching experiments reveal extreme 96 Zr enrichments in alteration minerals, showing that they incorporated supernova material hosted in interstellar ices. We show that the Solar System’s zirconium isotope variability reflects mixing between these ices and an ice-free rocky component. Finally, the presence of supernova nuclides in a volatile carrier supports models where the Solar System’s nucleosynthetic variability was imparted by thermal processing of material in the protoplanetary disk and during planetary accretion. This study shows that supernova material was delivered to the early Solar System by interstellar ices, explaining isotope variations and revealing that even inner planets like Earth and Mars accreted water-rich material from the outer Solar System.

Stable-isotope variations exist among inner solar system solids, planets, and asteroids, but their importance is not understood. We report correlated, mass-independent variations of titanium-46 and titanium-50 in bulk analyses of these materials. Because titanium-46 and titanium-50 have different nucleosynthetic origins, this correlation suggests that the presolar dust inherited from the protosolar molecular cloud was well mixed when the oldest solar system solids formed, but requires a subsequent process imparting isotopic variability at the planetary scale. We infer that thermal processing of molecular cloud material, probably associated with volatile-element depletions in the inner solar system, resulted in selective destruction of thermally unstable, isotopically anomalous presolar components, producing residual isotopic heterogeneity. This implies that terrestrial planets accreted from thermally processed solids with nonsolar isotopic compositions.