1
|
Zhang B, Chabot NL, Rubin AE. Compositions of iron-meteorite parent bodies constrain the structure of the protoplanetary disk. Proc Natl Acad Sci U S A 2024; 121:e2306995121. [PMID: 38805273 PMCID: PMC11161762 DOI: 10.1073/pnas.2306995121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 04/08/2024] [Indexed: 05/30/2024] Open
Abstract
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System, and they preserve information about conditions and planet-forming processes in the solar nebula. In this study, we include comprehensive elemental compositions and fractional-crystallization modeling for iron meteorites from the cores of five differentiated asteroids from the inner Solar System. Together with previous results of metallic cores from the outer Solar System, we conclude that asteroidal cores from the outer Solar System have smaller sizes, elevated siderophile-element abundances, and simpler crystallization processes than those from the inner Solar System. These differences are related to the formation locations of the parent asteroids because the solar protoplanetary disk varied in redox conditions, elemental distributions, and dynamics at different heliocentric distances. Using highly siderophile-element data from iron meteorites, we reconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across the protoplanetary disk within the first million years of Solar-System history. CAIs, the first solids to condense in the Solar System, formed close to the Sun. They were, however, concentrated within the outer disk and depleted within the inner disk. Future models of the structure and evolution of the protoplanetary disk should account for this distribution pattern of CAIs.
Collapse
Affiliation(s)
- Bidong Zhang
- Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA90095-1567
| | - Nancy L. Chabot
- Space Exploration Sector, Johns Hopkins University Applied Physics Laboratory, Laurel, MD20723
| | - Alan E. Rubin
- Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA90095-1567
- Maine Mineral and Gem Museum, Bethel, ME04217
| |
Collapse
|
2
|
Wang W, Walter MJ, Brodholt JP, Huang S. Early planetesimal differentiation and late accretion shaped Earth's nitrogen budget. Nat Commun 2024; 15:4169. [PMID: 38755135 PMCID: PMC11099130 DOI: 10.1038/s41467-024-48500-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Accepted: 05/02/2024] [Indexed: 05/18/2024] Open
Abstract
The relative roles of protoplanetary differentiation versus late accretion in establishing Earth's life-essential volatile element inventory are being hotly debated. To address this issue, we employ first-principles calculations to investigate nitrogen (N) isotope fractionation during Earth's accretion and differentiation. We find that segregation of an iron core would enrich heavy N isotopes in the residual silicate, while evaporation within a H2-dominated nebular gas produces an enrichment of light N isotope in the planetesimals. The combined effect of early planetesimal evaporation followed by core formation enriches the bulk silicate Earth in light N isotopes. If Earth is comprised primarily of enstatite-chondrite-like material, as indicated by other isotope systems, then late accretion of carbonaceous-chondrite-like material must contribute ~ 30-100% of the N budget in present-day bulk silicate Earth. However, mass balance using N isotope constraints shows that the late veneer contributes only a limited amount of other volatile elements (e.g., H, S, and C) to Earth.
Collapse
Affiliation(s)
- Wenzhong Wang
- Deep Space Exploration Lab/School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, 230026, China.
- CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui, China.
- Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, 20015, USA.
- Department of Earth Sciences, University College London, London, WC1E 6BT, UK.
| | - Michael J Walter
- Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, 20015, USA
| | - John P Brodholt
- Department of Earth Sciences, University College London, London, WC1E 6BT, UK
- The Centre of Planetary Habitability, University of Oslo, Oslo, Norway
| | - Shichun Huang
- Department of Earth, Environmenral, & Planetary Sciences, University of Tennessee at Knoxville, Knoxville, TN, USA
| |
Collapse
|
3
|
Graham RJ, Lichtenberg T, Pierrehumbert RT. CO 2 Ocean Bistability on Terrestrial Exoplanets. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2022; 127:e2022JE007456. [PMID: 36589718 PMCID: PMC9787872 DOI: 10.1029/2022je007456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 09/26/2022] [Accepted: 09/29/2022] [Indexed: 06/17/2023]
Abstract
Cycling of carbon dioxide between the atmosphere and interior of rocky planets can stabilize global climate and enable planetary surface temperatures above freezing over geologic time. However, variations in global carbon budget and unstable feedback cycles between planetary sub-systems may destabilize the climate of rocky exoplanets toward regimes unknown in the Solar System. Here, we perform clear-sky atmospheric radiative transfer and surface weathering simulations to probe the stability of climate equilibria for rocky, ocean-bearing exoplanets at instellations relevant for planetary systems in the outer regions of the circumstellar habitable zone. Our simulations suggest that planets orbiting G- and F-type stars (but not M-type stars) may display bistability between an Earth-like climate state with efficient carbon sequestration and an alternative stable climate equilibrium where CO2 condenses at the surface and forms a blanket of either clathrate hydrate or liquid CO2. At increasing instellation and with ineffective weathering, the latter state oscillates between cool, surface CO2-condensing and hot, non-condensing climates. CO2 bistable climates may emerge early in planetary history and remain stable for billions of years. The carbon dioxide-condensing climates follow an opposite trend in pCO2 versus instellation compared to the weathering-stabilized planet population, suggesting the possibility of observational discrimination between these distinct climate categories.
Collapse
Affiliation(s)
- R. J. Graham
- Atmospheric, Oceanic and Planetary PhysicsDepartment of PhysicsUniversity of OxfordOxfordUK
| | - Tim Lichtenberg
- Atmospheric, Oceanic and Planetary PhysicsDepartment of PhysicsUniversity of OxfordOxfordUK
| | | |
Collapse
|
4
|
Zhang B, Chabot NL, Rubin AE. Compositions of carbonaceous-type asteroidal cores in the early solar system. SCIENCE ADVANCES 2022; 8:eabo5781. [PMID: 36112692 PMCID: PMC9481128 DOI: 10.1126/sciadv.abo5781] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Accepted: 08/01/2022] [Indexed: 06/15/2023]
Abstract
The parent cores of iron meteorites belong to the earliest accreted bodies in the solar system. These cores formed in two isotopically distinct reservoirs: noncarbonaceous (NC) type and carbonaceous (CC) type in the inner and outer solar system, respectively. We measured elemental compositions of CC-iron groups and used fractional crystallization modeling to reconstruct the bulk compositions and crystallization processes of their parent asteroidal cores. We found generally lower S and higher P in CC-iron cores than in NC-iron cores and higher HSE (highly siderophile element) abundances in some CC-iron cores than in NC-iron cores. We suggest that the different HSE abundances among the CC-iron cores are related to the spatial distribution of refractory metal nugget-bearing calcium aluminum-rich inclusions (CAIs) in the protoplanetary disk. CAIs may have been transported to the outer solar system and distributed heterogeneously within the first million years of solar system history.
Collapse
Affiliation(s)
- Bidong Zhang
- Department of Earth, Planetary and Space Sciences, University California, Los Angeles, CA 90095-1567, USA
| | - Nancy L. Chabot
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
| | - Alan E. Rubin
- Department of Earth, Planetary and Space Sciences, University California, Los Angeles, CA 90095-1567, USA
- Maine Mineral and Gem Museum, 99 Main Street, P.O. Box 500, Bethel, ME 04217, USA
| |
Collapse
|
5
|
Nitrogen isotope evidence for Earth's heterogeneous accretion of volatiles. Nat Commun 2022; 13:4769. [PMID: 35970934 PMCID: PMC9378614 DOI: 10.1038/s41467-022-32516-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2022] [Accepted: 07/28/2022] [Indexed: 11/08/2022] Open
Abstract
The origin of major volatiles nitrogen, carbon, hydrogen, and sulfur in planets is critical for understanding planetary accretion, differentiation, and habitability. However, the detailed process for the origin of Earth's major volatiles remains unresolved. Nitrogen shows large isotopic fractionations among geochemical and cosmochemical reservoirs, which could be used to place tight constraints on Earth's volatile accretion process. Here we experimentally determine N-partitioning and -isotopic fractionation between planetary cores and silicate mantles. We show that the core/mantle N-isotopic fractionation factors, ranging from -4‰ to +10‰, are strongly controlled by oxygen fugacity, and the core/mantle N-partitioning is a multi-function of oxygen fugacity, temperature, pressure, and compositions of the core and mantle. After applying N-partitioning and -isotopic fractionation in a planetary accretion and core-mantle differentiation model, we find that the N-budget and -isotopic composition of Earth's crust plus atmosphere, silicate mantle, and the mantle source of oceanic island basalts are best explained by Earth's early accretion of enstatite chondrite-like impactors, followed by accretion of increasingly oxidized impactors and minimal CI chondrite-like materials before and during the Moon-forming giant impact. Such a heterogeneous accretion process can also explain the carbon-hydrogen-sulfur budget in the bulk silicate Earth. The Earth may thus have acquired its major volatile inventory heterogeneously during the main accretion phase.
Collapse
|
6
|
Miyazaki Y, Korenaga J. Inefficient Water Degassing Inhibits Ocean Formation on Rocky Planets: An Insight from Self-Consistent Mantle Degassing Models. ASTROBIOLOGY 2022; 22:713-734. [PMID: 35235378 DOI: 10.1089/ast.2021.0126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
A sufficient amount of water is required at the surface to develop water oceans. A significant fraction of water, however, remains in the mantle during magma ocean solidification, and thus the existence of water oceans is not guaranteed even for exoplanets located in the habitable zone. To discuss the likelihood of ocean formation, we built two models to predict the rate of mantle degassing during the magma ocean stage and the subsequent solid-state convection stage. We find that planets with low H2O/CO2 ratios would not have a sufficient amount of surface water to develop water oceans immediately after magma ocean solidification, and the majority of the water inventory would be retained in the mantle during their subsequent evolution regardless of planetary size. This is because oceanless planets are likely to operate under stagnant lid convection, and for such planets, dehydration stiffening of the depleted lithospheric mantle would limit the rate of mantle degassing. In contrast, a significant fraction of CO2 would already be degassed during magma ocean solidification. With a strong greenhouse effect, all surface water would exist as vapor, and water oceans may be absent throughout planetary evolution. Volatile concentrations in the bulk silicate Earth are close to the threshold amount for ocean formation, so if Venus shared similar concentrations, small differences in solar radiation may explain the divergent evolutionary paths of Earth and Venus.
Collapse
Affiliation(s)
- Yoshinori Miyazaki
- Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
| | - Jun Korenaga
- Department of Earth and Planetary Sciences, Yale University, New Haven, Connecticut, USA
| |
Collapse
|