Steam Atmospheres and Magma Oceans on Planets

2020 ◽  
Author(s):  
Keiko Hamano
Keyword(s):  
Feedback Loop ◽  
Radiative Energy ◽  
Terrestrial Planets ◽  
Magma Ocean ◽  
Planetary Body ◽  
Oxidation Of H2 ◽  
Giant Impacts ◽  
Magma Oceans ◽  
Greenhouse Effects ◽  
Insight Into

A magma ocean is a global layer of partially or fully molten rocks. Significant melting of terrestrial planets likely occurs due to heat release during planetary accretion, such as decay heat of short-lived radionuclides, impact energy released by continuous planetesimal accretion, and energetic impacts among planetary-sized bodies (giant impacts). Over a magma ocean, all water, which is released upon impact or degassed from the interior, exists as superheated vapor, forming a water-dominated, steam atmosphere. A magma ocean extending to the surface is expected to interact with the overlying steam atmosphere through material and heat exchange. Impact degassing of water starts when the size of a planetary body becomes larger than Earth’s moon or Mars. The degassed water could build up and form a steam atmosphere on protoplanets growing by planetesimal accretion. The atmosphere has a role in preventing accretion energy supplied by planetesimals from escaping, leading to the formation of a magma ocean. Once a magma ocean forms, part of the steam atmosphere would start to dissolve into the surface magma due to the high solubility of water into silicate melt. Theoretical studies indicated that as long as the magma ocean is present, a negative feedback loop can operate to regulate the amount of the steam atmosphere and to stabilize the surface temperature so that a radiative energy balance is achieved. Protoplanets can also accrete the surrounding H2-rich disk gas. Water could be produced by oxidation of H2 by ferrous iron in the magma. The atmosphere and water on protoplanets could be a mixture of outgassed and disk-gas components. Planets formed by giant impact would experience a global melting on a short timescale. A steam atmosphere could grow by later outgassing from the interior. Its thermal blanketing and greenhouse effects are of great importance in controlling the cooling rate of the magma ocean. Due to the presence of a runaway greenhouse threshold, the crystallization timescale and water budget of terrestrial planets can depend on the orbital distance from the host star. The terrestrial planets in our solar system essentially have no direct record of their earliest history, whereas observations of young terrestrial exoplanets may provide us some insight into what early terrestrial planets and their atmosphere are like. Evolution of protoplanets in the framework of pebble accretion remains unexplored.

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 Direct imaging of molten protoplanets in nearby young stellar associations

2019 ◽  
Vol 621 ◽  
pp. A125 ◽  
Author(s):  
Irene Bonati ◽  
Tim Lichtenberg ◽  
Dan J. Bower ◽  
Miles L. Timpe ◽  
Sascha P. Quanz
Keyword(s):  
Planet Formation ◽  
Magma Ocean ◽  
Direct Imaging ◽  
Origin And Evolution ◽  
Giant Impacts ◽  
Formation And Evolution ◽  
Magma Oceans ◽  
Rocky Planets ◽  
Stellar Associations

During their formation and early evolution, rocky planets undergo multiple global melting events due to accretionary collisions with other protoplanets. The detection and characterization of their post-collision afterglows (magma oceans) can yield important clues about the origin and evolution of the solar and extrasolar planet population. Here, we quantitatively assess the observational prospects to detect the radiative signature of forming planets covered by such collision-induced magma oceans in nearby young stellar associations with future direct imaging facilities. We have compared performance estimates for near- and mid-infrared instruments to be installed at ESO’s Extremely Large Telescope (ELT), and a potential space-based mission called Large Interferometer for Exoplanets (LIFE). We modelled the frequency and timing of energetic collisions using N-body models of planet formation for different stellar types, and determine the cooling of the resulting magma oceans with an insulating atmosphere. We find that the probability of detecting at least one magma ocean planet depends on the observing duration and the distribution of atmospheric properties among rocky protoplanets. However, the prospects for detection significantly increase for young and close stellar targets, which show the highest frequencies of giant impacts. For intensive reconnaissance with a K band (2.2 μm) ELT filter or a 5.6 μm LIFE filter, the β Pictoris, Columba, TW Hydrae, and Tucana-Horologium associations represent promising candidates for detecting a molten protoplanet. Our results motivate the exploration of magma ocean planets using the ELT and underline the importance of space-based direct imaging facilities to investigate and characterize planet formation and evolution in the solar vicinity. Direct imaging of magma oceans will advance our understanding of the early interior, surface and atmospheric properties of terrestrial worlds.

scholarly journals 3D micro-environment regulates NF–κβ dependent adhesion to induce monocyte differentiation

2018 ◽  
Author(s):  
Anindita Bhattacharya ◽  
Mahesh Agarwal ◽  
Rachita Mukherjee ◽  
Prosenjit Sen ◽  
Deepak Kumar Sinha
Keyword(s):  
Positive Feedback ◽  
Feedback Loop ◽  
The Novel ◽  
Monocyte Adhesion ◽  
Cellular Functions ◽  
Monocyte Differentiation ◽  
Summary Statement ◽  
Necessary And Sufficient ◽  
Multiple Signaling ◽  
Insight Into

AbstractDifferentiation of monocytes entails their relocation from blood to the tissue, hence accompanied by an altered physicochemical micro-environment. While the mechanism by which the biochemical make-up of the micro-environment induces differentiation is known, the fluid-like to gel-like transition in the physical micro-environment is not well understood. Monocytes maintain non-adherent state to prevent differentiation. We establish that irrespective of the chemical makeup, a 3D gel-like micro-environment induces a positive-feedback loop of adhesion-MAPK-NF-κβ activation to facilitate differentiation. In 2D fluid-like micro-environment, adhesion alone is capable of inducing differentiation via the same positive-feedback signalling. Chemical inducer treatment in fluid-like micro-environment, increases the propensity of monocyte adhesion via a brief pulse of p-MAPK. The adhesion subsequently elicit differentiation, establishing that adhesion is both necessary and sufficient to induce differentiation in 2D/3D micro-environment. Our findings challenge the notion that adhesion is a result of monocyte differentiation. Rather it’s the adhesion which triggers the differentiation of monocytes. MAPK, and NF-κβ being key molecules of multiple signaling pathways, we hypothesize that biochemically inert 3D gel-like micro-environment would also influence other cellular functions.Summary statementThis article brings out a new insight into the novel mechanisms of monocyte differentiation solely driven by physical micro-environment and adhesion.

Boron Behavior During the Evolution of the Early Solar System: The First 180 Million Years

Elements ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 231-236 ◽  
Author(s):  
Charles K. Shearer ◽  
Steven B. Simon
Keyword(s):  
Solar System ◽  
Solar Nebula ◽  
Nuclear Reactions ◽  
Terrestrial Planets ◽  
The Sun ◽  
Planetary Formation ◽  
Light Elements ◽  
Early Solar System ◽  
Spallation Reactions ◽  
Magma Oceans

The behavior of boron during the early evolution of the Solar System provides the foundation for how boron reservoirs become established in terrestrial planets. The abundance of boron in the Sun is depleted relative to adjacent light elements, a result of thermal nuclear reactions that destroy boron atoms. Extant boron was primarily generated by spallation reactions. In the initial materials condensing from the solar nebula, boron was predominantly incorporated into plagioclase. Boron abundances in the terrestrial planets exhibit variability, as illustrated by B/Be. During planetary formation and differentiation, boron is redistributed by fluids at low temperature and during crystallization of magma oceans at high temperature.

On the fate of water in the formation of rocky planets

2021 ◽  
Author(s):  
Lindy Elkins-Tanton ◽  
Jenny Suckale ◽  
Sonia Tikoo
Keyword(s):  
Water Content ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Plate Tectonics ◽  
Solidus Temperature ◽  
Magma Ocean ◽  
Excess Water ◽  
Low Degree ◽  
Giant Impacts ◽  
Rocky Planets

<p>Rocky planets go through at least one and likely multiple magma ocean stages, produced by the giant impacts of accretion. Planetary data and models show that giant impacts do not dehydrate either the mantle or the atmosphere of their target planets. The magma ocean liquid consists of melted target material and melted impactor, and so will be dominated by silicate melt, and also contain dissolved volatiles including water, carbon, and sulfur compounds.</p><p>As the magma ocean cools and solidifies, water and other volatiles will be incorporated into the nominally anhydrous mantle phases up to their saturation limits, and will otherwise be enriched in the remaining, evolving magma ocean liquids. The water content of the resulting cumulate mantle is therefore the sum of the traces in the mineral grains, and any water in trapped interstitial liquids. That trapped liquid fraction may in fact be by far the largest contributor to the cumulate water budget.</p><p>The water and other dissolved volatiles in the evolving liquids may quickly reach the saturation limit of magmas near the surface, where pressure is low, but degassing the magma ocean is likely more difficult than has been assumed in some of our models. To degas into the atmosphere, the gases must exsolve from the liquid and form bubbles, and those bubbles must be able to rise quickly enough to avoid being dragged down by convection and re-dissolved at higher pressures. If bubbles are buoyant enough (that is, large enough) to decouple from flow and rise, then they are also dynamically unstable and liable to be torn into smaller bubbles and re-entrained. This conundrum led to the hypothesis that volatiles do not significantly degas until a high level of supersaturation is reached, and the bubbles form a buoyant layer and rise in diapirs in a continuum dynamics sense. This late degassing would have the twin effects of increasing the water content of the cumulates, and of speeding up cooling and solidification of the planet.</p><p>Once the mantle is solidified, the timeclock until the start of plate tectonics begins. Modern plate tectonics is thought to rely on water to lower the viscosity of the asthenosphere, but plate tectonics is also thought to be the process by which water is brought into the mantle. Magma ocean solidification, however, offers two relevant processes. First, following solidification the cumulate mantle is gravitationally unstable and overturns to stability, carrying water-bearing minerals from the upper mantle through the transition zone and into the lower mantle. Upon converting to lower-mantle phases, these minerals will release their excess water, since lower mantle phases have lower saturation limits, thus fluxing the upper mantle with water. Second, the mantle will be near its solidus temperature still, and thus its viscosity will be naturally low. When fluxed with excess water, the upper mantle would be expected to form a low degree melt, which if voluminous enough with rise to help form the earliest crust, and if of very low degree, will further reduce the viscosity of the asthenosphere.</p>

Coupled models of magma oceans and their primordial atmospheres: volatile speciation, cooling history, and impact of condensables

2021 ◽  
Author(s):  
Tim Lichtenberg ◽  
Robert J. Graham ◽  
Ryan Boukrouche ◽  
Raymond T. Pierrehumbert
Keyword(s):  
Extrasolar Planets ◽  
Initial Distribution ◽  
Magma Ocean ◽  
Coupled Models ◽  
Time Resolved ◽  
Planetary Evolution ◽  
Sensitive Dependence ◽  
History Of ◽  
Magma Oceans ◽  
Rocky Planets

<p>The earliest atmospheres of rocky planets originate from extensive volatile release during magma ocean epochs that occur during assembly of the planet. These establish the initial distribution of the major volatile elements between different chemical reservoirs that subsequently evolve via geological cycles. Current theoretical techniques are limited in exploring the anticipated range of compositional and thermal scenarios of early planetary evolution. However, these are of prime importance to aid astronomical inferences on the environmental context and geological history of extrasolar planets. In order to advance the potential synergies between exoplanet observations and inferrences on the earliest history and climate state of the solar system terrestial planets, I will present a novel numerical framework that links an evolutionary, vertically-resolved model of the planetary silicate mantle with a radiative-convective model of the atmosphere. Numerical simulations using this framework illustrate the sensitive dependence of mantle crystallization and atmosphere build-up on volatile speciation and predict variations in atmospheric spectra with planet composition that may be detectable with future observations of exoplanets. Magma ocean thermal sequences fall into three general classes of primary atmospheric volatile with increasing cooling timescale: CO, N<sub>2</sub>, and O<sub>2</sub> with minimal effect on heat flux, H<sub>2</sub>O, CO<sub>2</sub>, and CH<sub>4</sub> with intermediate influence, and H<sub>2</sub> with several orders of magnitude increase in solidification time and atmosphere vertical stratification. In addition to these time-resolved results, I will present a novel formulation and application of a multi-species moist-adiabat for condensable-rich magma ocean and archean earth analog atmospheres, and outline how the cooling of such atmospheres can lead to exotic climate states that provide testable predictions for terrestrial exoplanets.</p>

scholarly journals Circadian regulation of c-MYC in mice

2020 ◽  
Vol 117 (35) ◽  
pp. 21609-21617
Author(s):  
Zhenxing Liu ◽  
Christopher P. Selby ◽  
Yanyan Yang ◽  
Laura A. Lindsey-Boltz ◽  
Xuemei Cao ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Circadian Clock ◽  
Tumor Suppressors ◽  
Feedback Loop ◽  
Cell Cycle Progression ◽  
Regulatory Mechanism ◽  
Clock Genes ◽  
Circadian Regulation ◽  
Cycle Progression ◽  
Insight Into

The circadian clock is a global regulatory mechanism that controls the expression of 50 to 80% of transcripts in mammals. Some of the genes controlled by the circadian clock are oncogenes or tumor suppressors. Among theseMychas been the focus of several studies which have investigated the effect of clock genes and proteins onMyctranscription and MYC protein stability. Other studies have focused on effects ofMycmutation or overproduction on the circadian clock in comparison to their effects on cell cycle progression and tumorigenesis. Here we have used mice with mutations in the essential clock genesBmal1,Cry1,andCry2to gain further insight into the effect of the circadian clock on this important oncogene/oncoprotein and tumorigenesis. We find that mutation of bothCry1andCry2, which abolishes the negative arm of the clock transcription–translation feedback loop (TTFL), causes down-regulation of c-MYC, and mutation ofBmal1,which abolishes the positive arm of TTFL, causes up-regulation of the c-MYC protein level in mouse spleen. These findings must be taken into account in models of the clock disruption–cancer connection.

An insight into testis and gubernaculum dynamics of INSL3 - RXFP2 signalling during testicular descent in the dog

2010 ◽  
Vol 22 (5) ◽  
pp. 751 ◽  
Author(s):  
S. Arrighi ◽  
G. Bosi ◽  
D. Groppetti ◽  
M. Aralla ◽  
F. Cremonesi
Keyword(s):  
Sertoli Cells ◽  
Leydig Cells ◽  
Feedback Loop ◽  
Testicular Descent ◽  
Fetal Period ◽  
Male Development ◽  
Dog Testis ◽  
Gubernaculum Testis ◽  
Insight Into ◽  
Different Tissues

Insulin-like 3 (INSL3) plays a prominent role in male development and is supposed to induce the growth of the gubernaculum testis (g.t.), thus being directly involved in testicular descent in humans and rodents. This happens through activation of the RXFP2 receptor (GREAT or LGR8). The INSL3–RXFP2 complex is reputed to play an additional paracrine role in the testis, possibly acting as part of an autocrine feedback loop. The present work provides evidence of the immunolocalisation of INSL3 in the Leydig cells of canine fetuses and of the expression of RXFP2 receptor in different tissues of the g.t. of the same specimens. RXFP2 was localised at the cell membrane of g.t. muscle and connective cells, as well as in the epithelial cells of the developing excurrent ducts. Notably, RXFP2 immunoreactivity of the g.t. was limited to fetuses at ~35–45 days of gestation, which is also the fetal period when the endocrine compartment of the dog testis is active endocrinologically, as confirmed by the anti-P450c17 and anti-INSL3 immunoreactivities of the fetal Leydig cells, and by anti-Müllerian hormone immunoreactivity of the Sertoli cells. The same immunoreactivities were also evaluated in the testes of cryptorchid dogs of different ages. RXFP2 immunoreactivity was absent from genital tracts of cryptorchid testes and g.t. remnants.

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