A new theory on Mercury's origin

2020 ◽  
Author(s):  
Manuel Scherf ◽  
Nikolay Erkaev ◽  
Helmut Lammer
Keyword(s):  
Solar Nebula ◽  
Surface Composition ◽  
Building Blocks ◽  
The Body ◽  
Terrestrial Planets ◽  
Magma Ocean ◽  
Volatile Elements ◽  
Continuous Growth ◽  
Giant Impact ◽  
First Time

<p>Of all the terrestrial planets in the Solar System Mercury stands out with a remarkably high core-mantle ratio, with its core occupying about 85% of the planetary radius. Several different theories tried to explain its high Fe/Si-ratio; the giant impact theory (e.g. [1]) for instance argues that one or more giant impacts stripped away most of the Hermean mantle, while the core remained and formed the smallest of the terrestrial planets. Another theory explains the high density of Mercury through a partial volatilization during the time of the solar nebula (e.g. [2]). Here, proto-Mercury is assumed to be substantially more massive than at present-day with a composition close to those of the other terrestrial planets. When the planet was surrounded by the hot solar nebula, however, most of the mantle evaporated, ending up with present-day Mercury. Other theories argue with the particular primordial conditions of its orbital location that might have favored the accretion of dense and volatile poor building-blocks such as enstatite chondrites (e.g. [3,4]). Messenger, however, revealed a surface composition that is surprisingly rich in volatile and moderately volatile elements [4]. This is hardly compatible with the giant impact and vaporization theory but supports hypothesis that connect Mercury’s high core-mantle ratio to the particular conditions of its orbital location.</p> <p>Within this talk, we will for the first time present a new model that connects these conditions with accretion and partial planetary evaporation. We will argue that Mercury (in contrast to old evaporation theories) was released out of the nebula as a small planetary embryo, comparable in size to the moon, that was covered with a global magma ocean. While the embryo proceeds to grow through frequent impactors, (moderately) volatile elements evaporate from the magma ocean and are lost into space due to the high surface temperature, the low gravity of the body and the high XUV flux from the young Sun. Here, lighter and more volatile elements are preferentially lost from the embryo, while the heavier and less volatile elements escape less efficient. Due to the continuous growth of proto-Mercury, however, the gravitational energy will start to dominate over the thermal energy of the evaporated particles, making them harder and harder to escape, which ultimately halts the loss of moderately volatile elements. Mercury subsequently finalizes its accretion with relatively volatile rich material and evolves to the body we can observe at present-day. We simulated the escape of (moderately) volatile elements with an adopted version of a 1D hydrodynamic upper atmosphere model (e.g. [5]) and will present our results here for the first time.</p> <p><strong>References:</strong> [1] Benz, W. et al., Space Sciences Series of ISSI, Volume 26, p. 7., 2008. [2] Cameron, A.G.W., Icarus, Volume 64, Issue 2, p. 285-294., 1985. [3] Charlier, B. and Namur, O., Elements, Volume 15, p. 9-14, 2019. [4] Nittler, Larry R. et al., Science, Volume 333, Issue 6051, pp. 1847, 2011. []5 Erkaev, et al., MNRAS, Volume 460, Issue 2, p.1300-1309, 2016.</p>

Implications of magma oceans for astrophysical observations: mass-radius and atmospheric composition

2020 ◽  
Author(s):  
Dan J. Bower ◽  
Daniel Kitzmann ◽  
Aaron Wolf ◽  
Patrick Sanan ◽  
Caroline Dorn ◽  
...  
Keyword(s):  
Building Blocks ◽  
Atmospheric Composition ◽  
Terrestrial Planets ◽  
Iron Core ◽  
Magma Ocean ◽  
Static Structure ◽  
Emission Data ◽  
Modelling Framework ◽  
Magma Oceans ◽  
Structure Calculations

<div> <div> <div> <p>The earliest secondary atmosphere of a rocky planet originates from extensive volatile release during one or more magma ocean epochs that occur during and after the assembly of the planet. Magma oceans set the stage for the long-term evolution of terrestrial planets by establishing the major chemical reservoirs of the iron core and silicate mantle, chemical stratification within the mantle, and outgassed atmosphere. Furthermore, current and future exoplanet observations will favour the detection and characterisation of hot and warm planets, potentially with large outgassed atmospheres. In this study, we highlight the potential to combine models of coupled interior–atmosphere evolution with static structure calculations and modelled atmospheric spectra (transmission and emission). By combining these components in a common modelling framework, we acknowledge planets as dynamic entities and leverage their evolution to bridge planet formation, interior-atmosphere interaction, and observations.</p> <p>An interior–atmosphere model is combined with static structure calculations to track the evolving radius of a hot rocky mantle that is outgassing volatiles. We consider oxidised species CO2 and H2O and generate synthetic emission and transmission spectra for CO2 and H2O dominated atmospheres. Atmospheres dominated by CO2 suppress the outgassing of H2O to a greater extent than previously realised, since previous studies have applied an erroneous relationship between volatile mass and partial pressure. Furthermore, formation of a lid at the surface can tie the outgassing of H2O to the efficiency of heat transport through the lid, rather than the radiative timescale of the atmosphere. We extend this work to explore the speciation of a primary atmosphere that is constrained using meteoritic materials as proxies for the planetary building blocks, and find that a range of reducing and oxidising atmospheres are possible.</p> </div> </div> </div><div> <div> <div> <p>Our results demonstrate that a hot molten planet can have a radius several percent larger (about 5%, assuming Earth-like core size) than its equivalent solid counterpart, which may explain the larger radii of some close-in exoplanets. Outgassing of a low molar mass species (such as H2O, compared to CO2) can combat the continual contraction of a planetary mantle and even marginally increase the planetary radius. We further use our models to generate synthetic transmission and emission data to aid in the detection and characterisation of rocky planets via transits and secondary eclipses. Atmospheres of terrestrial planets around M-stars that are dominated by CO2 versus H2O could be distinguished by future observing facilities that have extended wavelength coverage (e.g., JWST). Incomplete magma ocean crystallisation, as may be the case for close-in terrestrial planets, or full or part retention of an early outgassed atmosphere, should be considered in the interpretation of observational data from current and future observing facilities.</p> </div> </div> </div>

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.

Compositions of chondrites

1988 ◽  
Vol 325 (1587) ◽  
pp. 535-544 ◽  
Keyword(s):  
Boundary Conditions ◽  
Physical Properties ◽  
Solar Nebula ◽  
Terrestrial Planets ◽  
Volatile Elements ◽  
High Loss ◽  
Innermost Part ◽  
Solar Abundances

A compilation of data on 78 elements in the nine groups of chondrites shows each to be isochemical with the exception of a few volatiles. With the exception of the most volatile elements, the groups have solar abundances to within a factor of two. The solar abundances and the chemical and physical properties of phases in the leastaltered chondrites indicate formation by grain agglomeration in the preplanetary nebula. Planets formed by the gradual growth of bodies in the solar nebula. Because there is no evidence for the formation of non-chondritic bodies in the nebula, the simplest model calls for the bulk compositions of the terrestrial planets to be chondritic. Mercury is enriched in metal, perhaps either because of high loss of silicates due to enhanced radial drag in the innermost part of the nebula, or because of enhanced accretion of metallic cores from disrupted asteroids. Chondritic compositions should be considered as boundary conditions for planetary models.

The behaviour of MgO in a giant impact setting

2021 ◽  
Author(s):  
Tim Bögels ◽  
Razvan Caracas
Keyword(s):  
Building Materials ◽  
Melting Curve ◽  
Chemical Species ◽  
Building Blocks ◽  
The Body ◽  
Ab Initio Molecular Dynamics ◽  
Horizon 2020 ◽  
Giant Impact ◽  
Research And Innovation ◽  
The Impact

<p>The Earth-Moon system and its formation is a topic of great scientific interest, and great debate over the past decades. The giant impact hypothesis is the currently accepted model to explain the formation of our moon. Accordingly, a mars-sized impactor collides with the proto-earth. This giant impact vaporized a significant portion of the impactor and the proto-earth, creating a large accretionary disk from which the moon subsequently formed. Currently, there is a large effort to build reliable thermodynamic descriptors for the building materials of the two bodies involved in the impact. Understanding the behavior of major rock-forming minerals under these extreme conditions is vital for increasing the accuracy of these models.</p><p>Magnesium oxide, MgO, is one of the fundamental building blocks for rocky planets. It is an archetype material of ionic solids and a well-known refractory material. Because of its relevance it has been studied extensively; experimental and theoretical results have been produced up to pressures of 800 GPa and temperatures reaching 20000 K. These pressure and temperature regions are of great interest for the planetary sciences, studying planetary interiors. The transformation of the face-centered B1 phase to the body-centered B2 phase and the associated melting curve have been modelled numerous times. In contrast, we know very little of the liquid behaviour of MgO under pressure, let alone at the low pressures found in accretionary disks.</p><p>Here we investigate the low-density high-temperature regime characteristic of after-shock isentropic release. We explore the subcritical and the supercritical regimes of MgO using ab initio molecular dynamics. We determine the position of the critical point and examine the structural and transport properties in the sub- and supercritical regimes. We find an elevated critical temperature in comparison with previously studied magnesium-silicates, in agreement to the refractory nature of MgO. Furthermore, we provide insight into the speciation of liquid MgO and the liquid-gas separation. We see a shift in Mg-O speciation towards lower degrees of coordination as the temperature is increased from 4000K to 10000K. This shift in speciation is less pronounced at higher densities. The majority of the chemical species forming the incipient gas phase consist of isolated Mg and O ions and some MgO and O<sub>2</sub>.</p><p>This research was supported by the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT to RC). We acknowledge access to supercomputing facilities via eDARI stl2816, PRACE RA4947, and Uninet2 NN9697K grants.</p>

scholarly journals Geochemical arguments for an Earth-like Moon-forming impactor

2014 ◽  
Vol 372 (2024) ◽  
pp. 20130244 ◽  
Author(s):  
Nicolas Dauphas ◽  
Christoph Burkhardt ◽  
Paul H. Warren ◽  
Teng Fang-Zhen
Keyword(s):  
Isotopic Composition ◽  
Solar Nebula ◽  
Building Blocks ◽  
Inversion Method ◽  
Stage Model ◽  
The Moon ◽  
Two Stage ◽  
Geochemical Evidence ◽  
Giant Impact ◽  
The Earth

Geochemical evidence suggests that the material accreted by the Earth did not change in nature during Earth's accretion, presumably because the inner protoplanetary disc had uniform isotopic composition similar to enstatite chondrites, aubrites and ungrouped achondrite NWA 5363/5400. Enstatite meteorites and the Earth were derived from the same nebular reservoir but diverged in their chemical evolutions, so no chondrite sample in meteorite collections is representative of the Earth's building blocks. The similarity in isotopic composition (Δ 17 O, ε 50 Ti and ε 54 Cr) between lunar and terrestrial rocks is explained by the fact that the Moon-forming impactor came from the same region of the disc as other Earth-forming embryos, and therefore was similar in isotopic composition to the Earth. The heavy δ 30 Si values of the silicate Earth and the Moon relative to known chondrites may be due to fractionation in the solar nebula/protoplanetary disc rather than partitioning of silicon in Earth's core. An inversion method is presented to calculate the Hf/W ratios and ε 182 W values of the proto-Earth and impactor mantles for a given Moon-forming impact scenario. The similarity in tungsten isotopic composition between lunar and terrestrial rocks is a coincidence that can be explained in a canonical giant impact scenario if an early formed embryo (two-stage model age of 10–20 Myr) collided with the proto-Earth formed over a more protracted accretion history (two-stage model age of 30–40 Myr).

A magma ocean origin for Mercury's earliest exosphere

2020 ◽  
Author(s):  
Diana Gamborino ◽  
Noah Jäggi ◽  
Dan J. Bower ◽  
Aaron Wolf ◽  
Paolo Sossi ◽  
...  
Keyword(s):  
Surface Composition ◽  
Building Blocks ◽  
Atmospheric Composition ◽  
Initial Surface ◽  
Magma Ocean ◽  
Loss Mechanism ◽  
Near Surface ◽  
Enstatite Chondrite ◽  
Atmospheric Loss ◽  
Rapid Evacuation

<p>MESSENGER observations used to constrain surface composition suggest a global magma ocean formed on early Mercury [1, 2]. Our study models the coupled evolution of the Hermean magma ocean and atmosphere, and determines the extent of exospheric loss from an atmosphere formed by evaporation of a magma ocean. Using our framework to couple the interior and exterior chemical reservoirs, we evaluate a range of possible atmospheric evolution scenarios for early Mercury. These include the possibility that Mercury was fully-accreted before a mantle stripping event caused by a giant impact [3] led to degassing, or alternatively that the building blocks of Mercury were already relatively volatile-free.</p> <p>Assuming an initial surface temperature of 2500 K and an oxygen fugacity fixed at 1 log unit below the Iron-Wüstite buffer, we find that the Hermean magma ocean cooled to 1500 K (the rheological transition) in around 400 to 9000 yrs, depending on the efficiency of radiative heat transfer in the atmosphere. We investigate the behaviour of two endmember cases: (1) a present-day sized Mercury that is volatile free and thus cools in a manner similar to that of a blackbody, and (2) a larger Mercury that is sufficiently volatile-rich to provide a greenhouse atmosphere that delays cooling. During the magma ocean stage, evaporation and sublimation of oxide components from the molten silicate magma contribute to the growth of the atmosphere, in addition to volatile outgassing. For the endmember case with initial volatile abundances based on enstatite chondrite-like precursors, the atmosphere is dominated by CO, CO<sub>2</sub>, H<sub>2</sub>, and H<sub>2</sub>O, with minor abundances of SiO, Na, K, Mg, and Fe gas species. For the endmember case without major volatiles (C, H), the atmospheric composition is dominated by metal- and metal oxide gas species only.</p> <p>We apply a Monte Carlo (MC) atmospheric loss model [4] to calculate exospheric losses for all pathways and find that photoionization is the dominant loss mechanism for early Mercury. Cases both with and without major volatiles reveal that the atmosphere lasts between 100 and 250 years before the near-surface of Mercury becomes solid. Preliminary MC results show that photo-dissociation considerably alters the atmospheric composition, efficiently breaking SiO<sub>2</sub> into SiO<sup>+</sup> and O. Solar wind and magnetospheric plasma leads to rapid evacuation of the ionized species from the neutral exosphere whereas oxygen is lost efficiently by Jeans escape.</p> <p>Using our coupled framework, future modelling efforts will aim to understand if and how the evaporation of the magma ocean of early Mercury has modified its surface composition, with a view to interpreting BepiColombo observations. Hence our work provides an important step to connect Mercury’s formation, earliest evolution, and upcoming observations.</p> <p>References: [1] Vander Kaaden, K. E. and McCubbin, F. M. (2016). Cosmochim. Ac., 173, 246–263. [2] Berthet, S., Malavergne, V., and Righter, K. (2009). Geochim. Cosmochim. Ac., 73(20), 6402–6420. [3] Benz, W., et al. (2008). Mercury, pp. 7–20. Springer. [4] Wurz, P., and Lammer, H. (2003). <em>Icarus</em>, <em>164</em>(1), 1–13</p> <p> </p> <p> </p>

scholarly journals Origins and Early Evolution of the Atmosphere and the Oceans

2020 ◽  
Vol 9 (2) ◽  
pp. 135-313
Author(s):  
Bernard Marty
Keyword(s):  
Solar System ◽  
Solar Nebula ◽  
Noble Gases ◽  
Building Blocks ◽  
Anthropogenic Activity ◽  
Outer Solar System ◽  
Volatile Elements ◽  
Isotopic Signatures ◽  
Early Atmosphere ◽  
The Earth

My journey in science began with the study of volcanic gases, sparking an interest in the origin, and ultimate fate, of the volatile elements in the interior of our planet. How did these elements, so crucial to life and our surface environment, come to be sequestered within the deepest regions of the Earth, and what can they tell us about the processes occurring there? My approach has been to establish geochemical links between the noble gases, physical tracers par excellence, with major volatile elements of environmental importance, such as water, carbon and nitrogen, in mantle-derived rocks and gases. From these analyses we have learned that the Earth is relatively depleted in volatile elements when compared to its potential cosmochemical ancestors (e.g., ~2 ppm nitrogen compared to several hundreds of ppm in primitive meteorites) and that natural fluxes of carbon are two orders of magnitude lower than those emitted by current anthropogenic activity. Further insights into the origin of terrestrial volatiles have come from space missions that documented the composition of the proto-solar nebula and the outer solar system. The consensus behind the origin of the atmosphere and the oceans is evolving constantly, although recently a general picture has started to emerge. At the dawn of the solar system, the volatile-forming elements (H, C, N, noble gases) that form the majority of our atmosphere and oceans were trapped in solid dusty phases (mostly in ice beyond the snowline and organics everywhere). These phases condensed from the proto-solar nebula gas, and/or were inherited from the interstellar medium. These accreted together within the next few million years to form the first planetesimals, some of which underwent differentiation very early on. The isotopic signatures of volatiles were also fixed very early and may even have preceded the first episodes of condensation and accretion. Throughout the accretion of the Earth, volatile elements were delivered by material from both the inner (dry, volatile-poor) and outer (volatile-rich) solar system. This delivery was concomitant with the metals and silicates that form the bulk of the planet. The contribution of bodies that formed in the far outer solar system, a region now populated by comets, is likely to have been very limited. In that sense, volatile elements were contributed continuously throughout Earth’s accretion from inner solar system reservoirs, which also provided the silicates and metal building blocks of the inner planets. Following accretion, it likely took a few hundred million years for the Earth’s atmosphere and oceans to stabilise. Luckily, we have been able to access a compositional record of the early atmosphere and oceans through the analysis of palaeo-atmospheric fluids trapped in Archean hydrothermal quartz. From these analyses, it appears that the surface reservoirs of the Earth evolved due to interactions between the early Sun and the top of the atmosphere, as well as the development of an early biosphere that progressively altered its chemistry.

Probing the Substrate Promiscuity of Isopentenyl Phosphate Kinase as a Platform for Hemiterpene Analogue Production

2019 ◽  
Author(s):  
Sean Lund ◽  
Taylor Courtney ◽  
Gavin Williams
Keyword(s):  
Synthetic Biology ◽  
Building Blocks ◽  
Isoprenoid Biosynthesis ◽  
Thermoplasma Acidophilum ◽  
Substrate Promiscuity ◽  
Enzymatic Pathways ◽  
First Time ◽  
Rate Limiting ◽  
Alcohol Dependent ◽  
Isopentenyl Phosphate

Isoprenoids are a large class of natural products with wide-ranging applications. Synthetic biology approaches to the manufacture of isoprenoids and their new-to-nature derivatives are limited due to the provision in Nature of just two hemiterpene building blocks for isoprenoid biosynthesis. To address this limitation, artificial chemo-enzymatic pathways such as the alcohol-dependent hemiterpene pathway (ADH) serve to leverage consecutive kinases to convert exogenous alcohols to pyrophosphates that could be coupled to downstream isoprenoid biosynthesis. To be successful, each kinase in this pathway should be permissive of a broad range of substrates. For the first time, we have probed the promiscuity of the second enzyme in the ADH pathway, isopentenyl phosphate kinase from Thermoplasma acidophilum, towards a broad range of acceptor monophosphates. Subsequently, we evaluate the suitability of this enzyme to provide non-natural pyrophosphates and provide a critical first step in characterizing the rate limiting steps in the artificial ADH pathway.<br>

scholarly journals Physiology and Physical Chemistry of Bile Acids

2021 ◽  
Vol 22 (4) ◽  
pp. 1780
Author(s):  
Maria Chiara di Gregorio ◽  
Jacopo Cautela ◽  
Luciano Galantini
Keyword(s):  
Physical Chemistry ◽  
Bile Acids ◽  
Material Science ◽  
Metabolic Regulation ◽  
Enterohepatic Circulation ◽  
Building Blocks ◽  
The Body ◽  
Active Molecule ◽  
Supramolecular Aggregates ◽  
Biological Field

Bile acids (BAs) are facial amphiphiles synthesized in the body of all vertebrates. They undergo the enterohepatic circulation: they are produced in the liver, stored in the gallbladder, released in the intestine, taken into the bloodstream and lastly re-absorbed in the liver. During this pathway, BAs are modified in their molecular structure by the action of enzymes and bacteria. Such transformations allow them to acquire the chemical–physical properties needed for fulling several activities including metabolic regulation, antimicrobial functions and solubilization of lipids in digestion. The versatility of BAs in the physiological functions has inspired their use in many bio-applications, making them important tools for active molecule delivery, metabolic disease treatments and emulsification processes in food and drug industries. Moreover, moving over the borders of the biological field, BAs have been largely investigated as building blocks for the construction of supramolecular aggregates having peculiar structural, mechanical, chemical and optical properties. The review starts with a biological analysis of the BAs functions before progressively switching to a general overview of BAs in pharmacology and medicine applications. Lastly the focus moves to the BAs use in material science.

scholarly journals A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

Organics ◽  
2021 ◽  
Vol 2 (2) ◽  
pp. 107-117
Author(s):  
Mattia Forchetta ◽  
Valeria Conte ◽  
Giulia Fiorani ◽  
Pierluca Galloni ◽  
Federica Sabuzi
Keyword(s):  
Metal Oxides ◽  
Phosphonic Acid ◽  
Organic Molecules ◽  
Building Blocks ◽  
Reaction Conditions ◽  
Phosphonic Acids ◽  
Sustainable Improvement ◽  
Phosphonate Esters ◽  
First Time ◽  
Complex Organic

Owing to the attractiveness of organic phosphonic acids and esters in the pharmacological field and in the functionalization of conductive metal-oxides, the research of effective synthetic protocols is pivotal. Among the others, ω-bromoalkylphosphonates are gaining particular attention because they are useful building blocks for the tailored functionalization of complex organic molecules. Hence, in this work, the optimization of Michaelis–Arbuzov reaction conditions for ω-bromoalkylphosphonates has been performed, to improve process sustainability while maintaining good yields. Synthesized ω-bromoalkylphosphonates have been successfully adopted for the synthesis of new KuQuinone phosphonate esters and, by hydrolysis, phosphonic acid KuQuinone derivatives have been obtained for the first time. Considering the high affinity with metal-oxides, KuQuinones bearing phosphonic acid terminal groups are promising candidates for biomedical and photo(electro)chemical applications.

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