Constitution of terrestrial planets

1981 ◽  
Vol 303 (1477) ◽  
pp. 287-302 ◽  
Keyword(s):  
Bulk Composition ◽  
Parent Body ◽  
The Moon ◽  
Volatile Elements ◽  
Earth’S Mantle ◽  
The Earth ◽  
History Of ◽  
Relationship Of ◽  
Reduced State

Reliable estimates of the bulk composition are so far restricted to the three planetary objects from which we have samples for laboratory investigation, i.e. the Earth, the Moon and the eucrite parent asteroid. The last, the parent body of the eucrite— diogenite family of meteorites, an object that like Earth and Moon underwent magmatic differentiations, seems to have an almost chondritic composition except for a considerable depletion of all moderately volatile (Na, K, Rb, F, etc.) and highly volatile (Cl, Br, Cd, Pb, etc.) elements. The Moon is also depleted in moderately volatile and volatile elements compared to carbonaceous chondrites of type 1 (Cl) and also compared to the Earth. Again normalized to Cl and Si the Earth’s mantle and the Moon are slightly enriched in refractory lithophile elements and in magnesium. It might be that this enrichment is fictitious and only due to the normalization to Si and that both Earth’s mantle and Moon are depleted in Si, which partly entered the Earth’s core in metallic form. The striking depletion of the Earth’s mantle for the elements V, Cr and Mn can also be explained by their partial removal into the core. The similar abundances of V, Cr and Mn in the Moon and in the Earth’s mantle indicate the strong genetic relationship of Earth and Moon. Apart from their contents of metallic iron, all siderophile elements, moderately volatile and volatile elements, Earth and Moon are chemically very similar. It might well be that, with these exceptions and that of a varying degree of oxidation, all the inner planets have a similar chemistry. The chemical composition of the Earth’s mantle, for which reliable and accurate data have recently been obtained from the study of ultramafic nodules, yields important information about the accretion history of the Earth and that of the inner planets. It seems that accretion started with highly reduced material, with all Fe as metal and even Si and Cr, V and Mn partly in reduced state, followed by the accretion of more and more oxidized matter.

Chemical composition and accretion history of terrestrial planets

1988 ◽  
Vol 325 (1587) ◽  
pp. 545-557 ◽  
Keyword(s):  
Bulk Composition ◽  
Parent Body ◽  
Conclusive Evidence ◽  
Martian Surface ◽  
Volatile Elements ◽  
The Earth ◽  
Material Component ◽  
History Of ◽  
Siderophile Elements ◽  
High Concentrations

The high concentrations of moderately siderophile elements (Ni, Co, etc.) in the Earth’s mantle and the similarity of their Cl normalized abundances to those of moderately volatile elements (F, Na, K, Rb) and some elements such as In, which under solar nebula conditions are highly volatile, are striking. To account for the observed abundances, inhomogeneous accretion of the Earth from two components has been proposed. In this model accretion started with the highly reduced component A devoid of all elements more volatile than Na, followed by accretion of more and more oxidized material (component B), containing all elements in Cl abundances. Recent observations have brought almost conclusive evidence that SNC meteorites are martian surface rocks ejected by huge impacts. By assuming that Mars is indeed the parent body of SNC meteorites, the bulk composition of Mars is estimated. The data on the composition of Mars obtained in this way clearly show that the two-component model is also valid for Mars. The striking depletion of all elements with chalcophile character in the martian mantle indicates that, contrary to the Earth, Mars accreted almost homogeneously (H. Wanke, Phil. Trans. R. Soc. Lond . A 303, 287 (1981)).

scholarly journals Evaporative fractionation of volatile stable isotopes and their bearing on the origin of the Moon

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130259 ◽  
Author(s):  
James M. D. Day ◽  
Frederic Moynier
Keyword(s):  
Global Scale ◽  
Parent Body ◽  
The Moon ◽  
Magma Ocean ◽  
Volatile Elements ◽  
Giant Impact ◽  
The Earth ◽  
Present Distribution ◽  
Volatile Loss

The Moon is depleted in volatile elements relative to the Earth and Mars. Low abundances of volatile elements, fractionated stable isotope ratios of S, Cl, K and Zn, high μ ( 238 U/ 204 Pb) and long-term Rb/Sr depletion are distinguishing features of the Moon, relative to the Earth. These geochemical characteristics indicate both inheritance of volatile-depleted materials that formed the Moon and planets and subsequent evaporative loss of volatile elements that occurred during lunar formation and differentiation. Models of volatile loss through localized eruptive degassing are not consistent with the available S, Cl, Zn and K isotopes and abundance data for the Moon. The most probable cause of volatile depletion is global-scale evaporation resulting from a giant impact or a magma ocean phase where inefficient volatile loss during magmatic convection led to the present distribution of volatile elements within mantle and crustal reservoirs. Problems exist for models of planetary volatile depletion following giant impact. Most critically, in this model, the volatile loss requires preferential delivery and retention of late-accreted volatiles to the Earth compared with the Moon. Different proportions of late-accreted mass are computed to explain present-day distributions of volatile and moderately volatile elements (e.g. Pb, Zn; 5 to >10%) relative to highly siderophile elements (approx. 0.5%) for the Earth. Models of early magma ocean phases may be more effective in explaining the volatile loss. Basaltic materials (e.g. eucrites and angrites) from highly differentiated airless asteroids are volatile-depleted, like the Moon, whereas the Earth and Mars have proportionally greater volatile contents. Parent-body size and the existence of early atmospheres are therefore likely to represent fundamental controls on planetary volatile retention or loss.

Chemistry and accretion history of Mars

1994 ◽  
Vol 349 (1690) ◽  
pp. 285-293 ◽  
Keyword(s):  
Bulk Composition ◽  
Volcanic Gases ◽  
Martian Surface ◽  
Volatile Elements ◽  
Water Ice ◽  
The Earth ◽  
History Of ◽  
The Mean ◽  
Wet Climate ◽  
Martian Regolith

Using element correlations observed in SNC meteorites and general cosmochemical constraints, Wänke & Dreibus (1988) have estimated the bulk composition of Mars. The mean abundance value for moderately volatile elements Na, P, K, F, and Rb and most of the volatile elements like Cl, Br, and I in the Martian mantle exceed the terrestrial values by about a factor of two. The striking depletion of all elements with chalcophile character (Cu, Co, Ni, etc.) indicates that Mars, contrary to the Earth, accreted homogeneously, which also explains the obvious low abundance of water and carbon. SNC meteorites and especially the shergottites are very dry rocks, they also contain very little carbon, while the concentrations of chlorine and especially sulphur are higher than those in terrestrial rocks. As a consequence we should expect SO 2 and HC1 to be the most abundant compounds in Martian volcanic gases. This might explain the dominance of sulphur and chlorine in the Viking soils. In turn SO 2 , being an excellent greenhouse gas, may have been of major importance for the warm and wet period in the ancient Martian history. Episodic release of larger quantities of SO 2 stored in liquid or solid SO 2 tables in the Martian regolith triggered by volcanic intrusions as suggested here could lead to a large number of warm and wet climate periods of the order of a hundred years, interrupted by much longer cold periods characterized by water ice and liquid of solid SO 2 . Sulphur (FeS) probably also governs the oxygen fugacity of the Martian surface rocks.

Comparative chemical history of the Earth, the Moon and parent body of achondrite

1977 ◽  
Vol 285 (1327) ◽  
pp. 55-67 ◽  
Keyword(s):  
Major Elements ◽  
Parent Body ◽  
Chemical Fractionation ◽  
The Moon ◽  
Molten Layer ◽  
The Earth ◽  
Lunar Samples ◽  
History Of ◽  
Chemical History ◽  
Major Chemical

Chronological studies on the lunar samples suggest that major chemical fractionation occurred at 4.4 Ga. It is inferred from both whole-rock Rb-Sr isochron and Nd-Sm systematics. It is stressed that any models on the lunar petrogenesis and evolution should reconcile with this early fractionation. A model for chemical evolution of the Moon (extensive fractional crystallization of a molten layer, followed by impact melting and mixing of melts) is discussed to account for phase relations and r.e.e. abundances. Similar chronological characteristics are observed for achondrite parent body. Achondrite parent body experienced a similar evolutionary history to the Moon starting with a slightly different initial composition (major elements). In the Earth, on the contrary, chemical differentiation has continued (or is still continuing) as indicated by chronological and isotopic evidence.

The Bulk Composition of the Eucrite Parent Asteroid and its Bearing on Planetary Evolution

1980 ◽  
Vol 35 (2) ◽  
pp. 204-216 ◽  
Author(s):  
Gerlind Dreibus ◽  
Heinrich Wänke
Keyword(s):  
Genetic Relationship ◽  
Bulk Composition ◽  
Building Blocks ◽  
Parent Body ◽  
Strong Indication ◽  
Volatile Elements ◽  
Planetary Evolution ◽  
Incompatible Elements ◽  
Relationship Of ◽  
Binary Mixing

Abstract It is shown that howardites fit extraordinary well into a binary mixing diagram for both their major and trace element compositions. Eucrites and diogenites would be suitable endmembers. In the mixing diagram computed from the elemental compositions of howardites, we find at a certain position a composition with very special features. This composition designated PR* contains all refractory incompatible elements in almost C 1, i.e. primitive, abundances. If 43% olivine is added to PR* in order to match the C 1 value for the Mg/Si ratio, a composition is obtained which has almost exact C 1 abundance values for all lithophile elements of non-volatile character. Because of its probable genetic relation we have used an olivine composition equal to that of pallasites. An eucrite parent body (EPB) with eucrites, diogenites and pallasites as the major building blocks has been previously suggested by various authors.The bulk composition of the EPB, resulting from our computations is found to be almost chondritic, but with a considerable depletion of volatile and moderately volatile elements. A comparison of the bulk composition of the EPB with that of Earth and Moon reveals a number of remarkable differences. Thus, the similarity of the composition of the silicate phases of Earth and Moon becomes even more remarkable and must be taken as strong indication for the genetic relationship of Earth and Moon.

Early accretional history of the Earth and the Moon-forming event

Lithos ◽  
1993 ◽  
Vol 30 (3-4) ◽  
pp. 207-221 ◽  
Author(s):  
Stuart Ross Taylor
Keyword(s):  
The Moon ◽  
The Earth ◽  
History Of

scholarly journals Volatile loss following cooling and accretion of the Moon revealed by chromium isotopes

2018 ◽  
Vol 115 (43) ◽  
pp. 10920-10925 ◽  
Author(s):  
Paolo A. Sossi ◽  
Frédéric Moynier ◽  
Kirsten van Zuilen
Keyword(s):  
Atomic Mass Unit ◽  
The Moon ◽  
Volatile Elements ◽  
Mass Unit ◽  
Earth’S Mantle ◽  
Refractory Elements ◽  
Common Precursor ◽  
Lunar Rocks ◽  
Evaporative Loss ◽  
Volatile Loss

Terrestrial and lunar rocks share chemical and isotopic similarities in refractory elements, suggestive of a common precursor. By contrast, the marked depletion of volatile elements in lunar rocks together with their enrichment in heavy isotopes compared with Earth’s mantle suggests that the Moon underwent evaporative loss of volatiles. However, whether equilibrium prevailed during evaporation and, if so, at what conditions (temperature, pressure, and oxygen fugacity) remain unconstrained. Chromium may shed light on this question, as it has several thermodynamically stable, oxidized gas species that can distinguish between kinetic and equilibrium regimes. Here, we present high-precision Cr isotope measurements in terrestrial and lunar rocks that reveal an enrichment in the lighter isotopes of Cr in the Moon compared with Earth’s mantle by 100 ± 40 ppm per atomic mass unit. This observation is consistent with Cr partitioning into an oxygen-rich vapor phase in equilibrium with the proto-Moon, thereby stabilizing the CrO2 species that is isotopically heavy compared with CrO in a lunar melt. Temperatures of 1,600–1,800 K and oxygen fugacities near the fayalite–magnetite–quartz buffer are required to explain the elemental and isotopic difference of Cr between Earth’s mantle and the Moon. These temperatures are far lower than modeled in the aftermath of a giant impact, implying that volatile loss did not occur contemporaneously with impact but following cooling and accretion of the Moon.

Science and Exploration of the Moon: Overview

2021 ◽  
Author(s):  
Bradley L. Jolliff
Keyword(s):  
Solar System ◽  
Nearest Neighbor ◽  
Space Environment ◽  
Cold Trap ◽  
The Moon ◽  
Early Solar System ◽  
Geologic History ◽  
The Earth ◽  
History Of ◽  
The Impact

Earth’s moon, hereafter referred to as “the Moon,” has been an object of intense study since before the time of the Apollo and Luna missions to the lunar surface and associated sample returns. As a differentiated rocky body and as Earth’s companion in the solar system, much study has been given to aspects such as the Moon’s surface characteristics, composition, interior, geologic history, origin, and what it records about the early history of the Earth-Moon system and the evolution of differentiated rocky bodies in the solar system. Much of the Apollo and post-Apollo knowledge came from surface geologic exploration, remote sensing, and extensive studies of the lunar samples. After a hiatus of nearly two decades following the end of Apollo and Luna missions, a new era of lunar exploration began with a series of orbital missions, including missions designed to prepare the way for longer duration human use and further exploration of the Moon. Participation in these missions has become international. The more recent missions have provided global context and have investigated composition, mineralogy, topography, gravity, tectonics, thermal evolution of the interior, thermal and radiation environments at the surface, exosphere composition and phenomena, and characteristics of the poles with their permanently shaded cold-trap environments. New samples were recognized as a class of achondrite meteorites, shown through geochemical and mineralogical similarities to have originated on the Moon. New sample-based studies with ever-improving analytical techniques and approaches have also led to significant discoveries such as the determination of volatile contents, including intrinsic H contents of lunar minerals and glasses. The Moon preserves a record of the impact history of the solar system, and new developments in timing of events, sample based and model based, are leading to a new reckoning of planetary chronology and the events that occurred in the early solar system. The new data provide the grist to test models of formation of the Moon and its early differentiation, and its thermal and volcanic evolution. Thought to have been born of a giant impact into early Earth, new data are providing key constraints on timing and process. The new data are also being used to test hypotheses and work out details such as for the magma ocean concept, the possible existence of an early magnetic field generated by a core dynamo, the effects of intense asteroidal and cometary bombardment during the first 500 million–600 million years, sequestration of volatile compounds at the poles, volcanism through time, including new information about the youngest volcanism on the Moon, and the formation and degradation processes of impact craters, so well preserved on the Moon. The Moon is a natural laboratory and cornerstone for understanding many processes operating in the space environment of the Earth and Moon, now and in the past, and of the geologic processes that have affected the planets through time. The Moon is a destination for further human exploration and activity, including use of valuable resources in space. It behooves humanity to learn as much about Earth’s nearest neighbor in space as possible.

scholarly journals Accretion of the Moon from non-canonical discs

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130256 ◽  
Author(s):  
J. Salmon ◽  
R. M Canup
Keyword(s):  
Angular Momentum ◽  
Rotation Period ◽  
Major Axis ◽  
The Moon ◽  
Large Excess ◽  
Semi Major Axis ◽  
Earth’S Mantle ◽  
The Earth ◽  
Post Impact ◽  
Impact Simulations

Impacts that leave the Earth–Moon system with a large excess in angular momentum have recently been advocated as a means of generating a protolunar disc with a composition that is nearly identical to that of the Earth's mantle. We here investigate the accretion of the Moon from discs generated by such ‘non-canonical’ impacts, which are typically more compact than discs produced by canonical impacts and have a higher fraction of their mass initially located inside the Roche limit. Our model predicts a similar overall accretional history for both canonical and non-canonical discs, with the Moon forming in three consecutive steps over hundreds of years. However, we find that, to yield a lunar-mass Moon, the more compact non-canonical discs must initially be more massive than implied by prior estimates, and only a few of the discs produced by impact simulations to date appear to meet this condition. Non-canonical impacts require that capture of the Moon into the evection resonance with the Sun reduced the Earth–Moon angular momentum by a factor of 2 or more. We find that the Moon's semi-major axis at the end of its accretion is approximately 7 R ⊕ , which is comparable to the location of the evection resonance for a post-impact Earth with a 2.5 h rotation period in the absence of a disc. Thus, the dynamics of the Moon's assembly may directly affect its ability to be captured into the resonance.

The Earth-Moon Connection

1989 ◽  
Vol 44 (10) ◽  
pp. 891-923 ◽  
Author(s):  
A. E. Ringwood
Keyword(s):  
Genetic Relationship ◽  
The Moon ◽  
Core Formation ◽  
Earth’S Mantle ◽  
Terrestrial Atmosphere ◽  
The Earth ◽  
Wide Range ◽  
Siderophile Elements ◽  
The Impact ◽  
Close Genetic Relationship

Abstract The early thermal state of the Earth provides important constraints on hypotheses relating to its origin and its connection with the Moon. The currently popular giant impact hypothesis of lunar origin requires the Earth’s mantle to have been completely melted during the impact. Differentiation of a molten mantle would have produced strong chemical and mineralogical stratification, causing the mantle to become gravitationally stable and resistant to convective rehomogenization. The resulting composition and mineralogy of the upper mantle and primitive crust would have been dramatically different from those which have existed during the past 3.8 b. y. It is concluded that the Earth’s mantle was not extensively melted at the conclusion of accretion of the planet and therefore the hypothesis that the Moon was formed by the impact of a martian-sized planetesimal on the proto-Earth is probably incorrect. Nevertheless, a wide range of geochemical evidence demonstrates the existence of a close genetic relationship between the Moon and the Earth’s mantle. The key evidence relates to the processes of core formation in planetary bodies and resultant abundance patterns of siderophile elements which remain in their silicate mantles. Because of the complexity of the core formation process within a given body and the multiplicity of chemical and physical processes involved, the mantle siderophile signature is expected to be a unique characteristic. Thus, the siderophile signatures of Mars and of the eucrite parent body are quite distinct from that of the Earth’s mantle. Lunar siderophile geochemistry is reviewed in detail. It is demonstrated that a large group of siderophile elements display similar abundances in the terrestrial and lunar mantles. The similarity implies that a major proportion of the material now in the Moon was derived from the Earth’s mantle after core formation. This implication, however, does not require that the bulk compositions of the lunar and terrestrial mantles should be essentially identical, as is often assumed. Factors which may contribute to significant compositional differences between the two bodies within the context of a close genetic relationship are reviewed. The most promising mechanism for removing terrestrial material from the Earth’s mantle arises from the impacts of a number of large (0.001 to 0.01 ME) but not giant (≥ 0.1 ME) planetesimals after core formation and at the terminal stage of the Earth’s accretion. These impacts evaporated several times their own masses of mantle material and shock-melted considerably more. However, they did not lead to complete or extensive (e.g. > 50%) melting of the entire mantle. Impact-generated clouds of shock-melted spray and vapours were accelerated to high velocities in the presence of a primitive terrestrial atmosphere that co-rotated with the Earth. This provided an effective means of transferring angular momentum from the Earth to the ejected material which condensed to form a ring of Earth-orbiting planetesimals and moonlets. The Moon was formed by coagulation from material derived from the outer regions of this ring. Accretion of the Earth in the presence of the gases of the solar nebula and the co-rotating primitive terrestrial atmosphere may also have provided a mechanism for generating the rapid prograde spin of the proto-Earth.

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