Mercury and other iron-rich planetary bodies as relics of inefficient accretion

This work aims at exploring the scaling relations among rocky exoplanets. With the assumption of internal gravity increasing linearly in the core, and staying constant in the mantle, and tested against numerical simulations, a simple model is constructed, applicable to rocky exoplanets of core mass fraction (CMF) ∈ 0.1 ∼ 0.4 and mass ∈ 0.1 ∼ 10M ⊕ . Various scaling relations are derived: (1) core radius fraction CRF ≈ √ CMF, (2) Typical interior pressure P typical ∼ g · M p · R 2 p . These scaling relations, though approximate, are handy for quick use owing to their simplicity and lucidity, and provide insights into the interior structures of rocky exoplanets. As examples, this model is applied to several planets including Earth, GJ 1132b, , and made comparison with the numerical method.

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“…Note that Mercury lies outside this range of the CMF as it has a big core, owing to its likely giant impact origin (Asphaug & Reufer 2014).…”

Section: Introductionmentioning

confidence: 99%

A Simple Analytical Model for Rocky Planet Interiors

Zeng

Jacobsen

2017

ApJ

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“…The planetary size of this model is quite close to the present size of Mercury. Except for the model M4, the remaining models would require substantial removal of mantle by the proposed hit and run mechanism (Asphaug and Reufer ) in order to produce the estimated mantle thickness of ~400 km. The variations in the aluminum and iron abundances for the various models have significant influence on the initial abundance of the short‐lived nuclides, 26 Al and 60 Fe (Table ).…”

Section: Numerical Simulationsmentioning

confidence: 99%

“…Apart from the hypotheses proposed earlier regarding the formation of Mercury in an environment where metallic iron was present in high abundance (Wurm et al. ; Nayakshin ), the recent simulations by Asphaug and Reufer () provides an alternative scenario. The origin of Mercury as a survivor of one or more hit and run collision(s) of differentiated proto‐Mercury with a larger target planet, e.g., a protoEarth or protoVenus, has been proposed.…”

Section: Introductionmentioning

confidence: 99%

“…). We have explored the possibility of collision‐induced mantle stripping of the differentiated planet by the proposed hit and run mechanism (Asphaug and Reufer ) to explain its inner structure. We have also investigated the possibility of reproducing the inner structure of the planet on the basis of a suitable choice of the initial planetary composition without the need of the hit and run mechanism.…”

Section: Introductionmentioning

confidence: 99%

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Did ²⁶Al and impact‐induced heating differentiate Mercury?

Bhatia

Sahijpal

2016

Meteorit & Planetary Scien

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Numerical models dealing with the planetary scale differentiation of Mercury are presented with the short‐lived nuclide, 26Al, as the major heat source along with the impact‐induced heating during the accretion of planets. These two heat sources are considered to have caused differentiation of Mars, a planet with size comparable to Mercury. The chronological records and the thermal modeling of Mars indicate an early differentiation during the initial ~1 million years (Ma) of the formation of the solar system. We theorize that in case Mercury also accreted over an identical time scale, the two heat sources could have differentiated the planets. Although unlike Mars there is no chronological record of Mercury's differentiation, the proposed mechanism is worth investigation. We demonstrate distinct viable scenarios for a wide range of planetary compositions that could have produced the internal structure of Mercury as deduced by the MESSENGER mission, with a metallic iron (Fe‐Ni‐FeS) core of radius ~2000 km and a silicate mantle thickness of ~400 km. The initial compositions were derived from the enstatite and CB (Bencubbin) chondrites that were formed in the reducing environments of the early solar system. We have also considered distinct planetary accretion scenarios to understand their influence on thermal processing. The majority of our models would require impact‐induced mantle stripping of Mercury by hit and run mechanism with a protoplanet subsequent to its differentiation in order to produce the right size of mantle. However, this can be avoided if we increase the Fe‐Ni‐FeS contents to ~71% by weight. Finally, the models presented here can be used to understand the differentiation of Mercury‐like exoplanets and the planetary embryos of Venus and Earth.

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“…Impacts between planetary embryos of 0.1 to 1 Earth-mass were thought to be common during the late stages of planet formation in our Solar System, 200-300 Myr after the dissipation of the solar nebula (see e.g., [56] for discussion). A collision or multiple collisions have been suggested as an explanation for the anomalously iron-rich composition of the planet Mercury [57], the slow rotation rate and absence of moon for Venus [58], Earth's large moon [13][14][15][16], and the crustal dichotomy [59] and small satellites of Mars [60][61][62][63]. Pluto's satellites probably formed as a result of an impact between two Kuiper Belt objects [17,18,64].…”

Section: Satellite Formation Via Giant Impactmentioning

confidence: 99%

Formation of exomoons: a solar system perspective

Barr

2016

Astronomical Review

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Satellite formation is a natural by-product of planet formation. With the discovery of numerous extrasolar planets, it is likely that moons of extrasolar planets (exomoons) will soon be discovered. Some of the most promising techniques can yield both the mass and radius of the moon. Here, I review recent ideas about the formation of moons in our Solar System, and discuss the prospects of extrapolating these theories to predict the sizes of moons that may be discovered around extrasolar planets. It seems likely that planet-planet collisions could create satellites around rocky or icy planets which are large enough to be detected by currently available techniques. Detectable exomoons around gas giants may be able to form by co-accretion or capture, but determining the upper limit on likely moon masses at gas giant planets requires more detailed, modern simulations of these processes.

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Mercury and other iron-rich planetary bodies as relics of inefficient accretion

Cited by 156 publications

References 27 publications

A Simple Analytical Model for Rocky Planet Interiors

A Simple Analytical Model for Rocky Planet Interiors

Did ²⁶Al and impact‐induced heating differentiate Mercury?

Formation of exomoons: a solar system perspective

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Mercury and other iron-rich planetary bodies as relics of inefficient accretion

Cited by 156 publications

References 27 publications

A Simple Analytical Model for Rocky Planet Interiors

A Simple Analytical Model for Rocky Planet Interiors

Did 26Al and impact‐induced heating differentiate Mercury?

Formation of exomoons: a solar system perspective

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Did ²⁶Al and impact‐induced heating differentiate Mercury?