Anatomy of rocky planets formed by rapid pebble accretion

Johansen, Anders; Ronnet, Thomas; Schiller, Martin; Deng, Zhengbin; Bizzarro, Martin

doi:10.1051/0004-6361/202142141

Cited by 17 publications

(5 citation statements)

References 109 publications

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“…Nonetheless, these iron-meteorite parent bodies have relatively small core mass fractions, an average of 21% for NC-iron cores and 13% for CC-iron cores ( 31 ), compared with those of terrestrial planets: Mars at 25% ( 77 ) and Earth at 32.5% ( 78 ). If the iron-meteorite parent bodies are representative of initial accretion materials for terrestrial planets, later accretion of highly reduced materials (such as metal-rich pebbles) is needed to account for the relatively high core mass fractions of Mars and Earth ( 79 ).…”

Section: Discussionmentioning

confidence: 99%

Compositions of iron-meteorite parent bodies constrain the structure of the protoplanetary disk

Zhang,

Chabot,

Rubin

2024

Proc. Natl. Acad. Sci. U.S.A.

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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.

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Section: Discussionmentioning

confidence: 99%

Compositions of iron-meteorite parent bodies constrain the structure of the protoplanetary disk

Zhang,

Chabot,

Rubin

2024

Proc. Natl. Acad. Sci. U.S.A.

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“…Although the exact CMB temperature increase varies in different MGI models, it should be higher than that resulting from the core‐formation process during previous smaller impacts (Nimmo, 2022). Pebble accretion may also increase CMB temperatures, while recent studies suggest this mechanism is so efficient that it could melt the entire mantle (e.g., Johansen et al., 2023), leaving no solid mantle to produce strong mantle plumes. Our results show that the unique context caused by the MGI can give rise to strong mantle plumes capable of inducing subduction even when the maximum lithosphere yield strength is >150 MPa, which is noticeably higher than inversions based on present‐day plate tectonics (Rudi et al., 2022).…”

Section: Discussionmentioning

confidence: 99%

A Giant Impact Origin for the First Subduction on Earth

Yuan,

Gurnis,

Asimow

et al. 2024

Geophysical Research Letters

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Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. It remains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact (MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to the accumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, with some of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here, we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subduction initiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMB temperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements in LLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications for understanding the diverse tectonic regimes of rocky planets.

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“…In Paper I of this series (Johansen et al 2023a), we demonstrated how planetesimals forming outside the ice line melt and desiccate through heat release by the decay of 26 Al. Energy from the decay of 26 Al runs out after a few half-lives (t 1/2 = 0.7 Myr).…”

Section: Introductionmentioning

confidence: 97%

Anatomy of rocky planets formed by rapid pebble accretion

Johansen

Ronnet

Schiller

et al. 2023

A&A

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We explore the heating and differentiation of rocky planets that grow by rapid pebble accretion. Our terrestrial planets grow outside of the ice line and initially accrete 28% water ice by mass. The accretion of water stops after the protoplanet reaches a mass of 0.01 ME where the gas envelope becomes hot enough to sublimate the ice and transport the vapour back to the protoplanetary disc by recycling flows. The energy released by the decay of 26Al melts the accreted ice to form clay (phyllosilicates), oxidized iron (FeO), and a water surface layer with ten times the mass of Earth’s modern oceans. The ocean–atmosphere system undergoes a run-away greenhouse effect after the effective accretion temperature crosses a threshold of around 300 K. The run-away greenhouse process vaporizes the water layer, thereby trapping the accretion heat and heating the surface to more than 6000 K. This causes the upper part of the mantle to melt and form a global magma ocean. Metal melt separates from silicate melt and sediments towards the bottom of the magma ocean; the gravitational energy released by the sedimentation leads to positive feedback where the beginning differentiation of the planet causes the whole mantle to melt and differentiate. All rocky planets thus naturally experience a magma ocean stage. We demonstrate that Earth’s small excess of 182W (the decay product of 182Hf) relative to the chondrites is consistent with such rapid core formation within 5 Myr followed by equilibration of the W reservoir in Earth’s mantle with 182W-poor material from the core of a planetary-mass impactor, provided that the equilibration degree is at least 25–50%, depending on the initial Hf/W ratio. The planetary collision must have occurred at least 35 Myr after the main accretion phase of the terrestrial planets.

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Anatomy of rocky planets formed by rapid pebble accretion

Cited by 17 publications

References 109 publications

Compositions of iron-meteorite parent bodies constrain the structure of the protoplanetary disk

Compositions of iron-meteorite parent bodies constrain the structure of the protoplanetary disk

A Giant Impact Origin for the First Subduction on Earth

Anatomy of rocky planets formed by rapid pebble accretion

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