Articles de revues : « Atmosphère primordiale »

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Ragossnig, Florian, Alexander Stökl, Ernst Dorfi, Colin P. Johnstone, Daniel Steiner et Manuel Güdel. « Interaction of infalling solid bodies with primordial atmospheres of disk-embedded planets ». Astronomy & ; Astrophysics 618 (octobre 2018) : A19. http://dx.doi.org/10.1051/0004-6361/201832681.

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Context. Planets that form early enough to be embedded in the circumstellar gas disk accumulate thick atmospheres of nebular gas. Models of these atmospheres need to specify the surface luminosity (i.e. energy loss rate) of the planet. This luminosity is usually associated with a continuous inflow of solid bodies, where the gravitational energy released from these bodies is the source of energy. However, if these bodies release energy in the atmosphere instead of at the surface, this assumption might not be justified. Aims. Our aim is to explore the interactions of infalling planetesimals with primordial atmospheres at an embedded phase of evolution. We investigate effects of atmospheric interaction on the planetesimals (mass loss) and the atmosphere (heating/cooling). Methods. We used atmospheric parameters from a snapshot of time-dependent evolution simulations for embedded atmospheres and simulated purely radial, infall events of siliceous planetesimals in a 1D, explicit code. We implemented energy transfer between friction, radiation transfer by the atmosphere and the body, and thermal ablation; this gives us the possibility to examine the effects on the planetesimals and the atmosphere. Results. We find that a significant amount of gravitational energy is indeed dissipated into the atmosphere, especially for larger planetary cores, which consequently cannot contribute to the atmospheric planetary luminosity. Furthermore, we examine that planetesimal infall events for cores, MC > 2M⊕, which actually result in a local cooling of the atmosphere; this is totally in contradiction with the classical model.

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Modirrousta-Galian, Darius, et Jun Korenaga. « The Diffusion Limit of Photoevaporation in Primordial Planetary Atmospheres ». Astrophysical Journal 965, n^o 1 (1 avril 2024) : 97. http://dx.doi.org/10.3847/1538-4357/ad276f.

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Abstract Photoevaporation is thought to play an important role in early planetary evolution. In this study, we investigate the diffusion limit of X-ray- and ultraviolet-induced photoevaporation in primordial atmospheres. We find that compositional fractionation resulting from mass loss is more significant than currently recognized, because it is controlled by the conditions at the top of the atmosphere, where particle collisions are less frequent. Such fractionation at the top of the atmosphere develops a compositional gradient that extends downward. The mass outflow eventually reaches a steady state in which the hydrogen loss is diffusion-limited. We derive new analytic expressions for the diffusion-limited mass-loss rate and the crossover mass.

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Chance, Quadry, Sarah Ballard et Keivan Stassun. « Signatures of Impact-driven Atmospheric Loss in Large Ensembles of Exoplanets ». Astrophysical Journal 937, n^o 1 (1 septembre 2022) : 39. http://dx.doi.org/10.3847/1538-4357/ac8a97.

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Abstract The results of large-scale exoplanet transit surveys indicate that the distribution of small planet radii is likely sculpted by atmospheric loss. Several possible physical mechanisms exist for this loss of primordial atmospheres, each of which produces a different set of observational signatures. In this study, we investigate the impact-driven mode of atmosphere loss via N-body simulations. We compare the results from giant impacts, at a demographic level, to results from another commonly invoked method of atmosphere loss, photoevaporation. Applying two different loss prescriptions to the same sets of planets, we then examine the resulting distributions of planets with retained primordial atmospheres. As a result of this comparison, we identify two new pathways toward discerning the dominant atmospheric-loss mechanism at work. Both of these pathways involve using transit multiplicity as a diagnostic, in examining the results of follow-up atmospheric and radial velocity surveys.

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Kimura, Tadahiro, et Masahiro Ikoma. « Formation of aqua planets with water of nebular origin : effects of water enrichment on the structure and mass of captured atmospheres of terrestrial planets ». Monthly Notices of the Royal Astronomical Society 496, n^o 3 (22 juin 2020) : 3755–66. http://dx.doi.org/10.1093/mnras/staa1778.

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ABSTRACT Recent detection of exoplanets with Earth-like insolation attracts growing interest in how common Earth-like aqua planets are beyond the Solar system. While terrestrial planets are often assumed to capture icy or water-rich planetesimals, a primordial atmosphere of nebular origin itself can produce water through oxidation of the atmospheric hydrogen with oxidizing minerals from incoming planetesimals or the magma ocean. Thermodynamically, normal oxygen buffers produce water comparable in mole number equal to or more than hydrogen. Thus, the primordial atmosphere would likely be highly enriched with water vapour; however, the primordial atmospheres have been always assumed to have the solar abundances. Here we integrate the 1D structure of such an enriched atmosphere of sub-Earths embedded in a protoplanetary disc around an M dwarf of 0.3$\, \mathrm{M}_\odot$ and investigate the effects of water enrichment on the atmospheric properties with focus on water amount. We find that the well-mixed highly enriched atmosphere is more massive by a few orders of magnitude than the solar-abundance atmosphere, and that even a Mars-mass planet can obtain water comparable to the present Earth’s oceans. Although close-in Mars-mass planets likely lose the captured water via disc dispersal and photoevaporation, these results suggest that there are more sub-Earths with Earth-like water contents than previously predicted. How much water terrestrial planets really obtain and retain against subsequent loss, however, depends on efficiencies of water production, mixing in the atmosphere and magma ocean, and photoevaporation, detailed investigation for which should be made in the future.

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Montoya, David. « Hostilidad perpetua, transformaciones transitorias : Persona, cuerpo y moralidad entre los tsotsiles de Chamula, Chiapas / Perpetual hostility, transitory transformations : Person, body and morality between the tsotsiles of Chamula, Chiapas ». Revista Trace, n^o 78 (31 juillet 2020) : 67. http://dx.doi.org/10.22134/trace.78.2020.735.

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El actual estudio etnográfico da cuenta de que lo chon –un aspecto de la persona, generalmente, asociado a lo animal– está relacionado con un estado de permanente hostilidad, presente en el mundo desde tiempos primordiales. Este aspecto, a la vez que potencia la vulnerabilidad entre los humanos, resalta la fortaleza de otros seres, como Dios y el Pukuj. En la búsqueda de lidiar con esa atmósfera de hostilidad y, de mitigar su propia vulnerabilidad, la humanidad experimenta múltiples transformaciones morales-corporales.Abstract: This ethnographic study shows that the chon –an aspect of the person, generally associated with the animal– is related to an state of permanent hostility, given in the world since primordial times. Although this aspect, while enhancing vulnerability among humans, highlights the strength of other beings such as God and the Pukuj. Therefore, to deal with this atmosphere of hostility and, therefore, to mitigate its own vulnerability, humanity undergoes multiple transformations moral-bodily. Keywords: chon; tsotsiles; humanity; vulnerability; morale.Résumé : Cette étude ethnographique montre que le chon –un aspect de la personne, généralment associé à l’animal– est lié à l’état d’hostilité qui caractérise le monde. Cet aspect, tout en renforçant la vulnérabilité des humains, met en évidence la force d’autres êtres tels que Dieu et les Pukuj. Dans sa quête pour faire face à cette atmosphère d’hostilité et, par conséquent, pour atténuer sa propre vulnérabilité, l’humanité subit de multiples transformations morales-corporelles.Mots-clés: chon ; tsotsiles ; vulnérabilité ; humanité ; moral.

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Sinclair, Catriona A., Mark C. Wyatt, Alessandro Morbidelli et David Nesvorný. « Evolution of the Earth’s atmosphere during Late Veneer accretion ». Monthly Notices of the Royal Astronomical Society 499, n^o 4 (16 octobre 2020) : 5334–62. http://dx.doi.org/10.1093/mnras/staa3210.

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ABSTRACT Recent advances in our understanding of the dynamical history of the Solar system have altered the inferred bombardment history of the Earth during accretion of the Late Veneer, after the Moon-forming impact. We investigate how the bombardment by planetesimals left-over from the terrestrial planet region after terrestrial planet formation, as well as asteroids and comets, affects the evolution of Earth’s early atmosphere. We develop a new statistical code of stochastic bombardment for atmosphere evolution, combining prescriptions for atmosphere loss and volatile delivery derived from hydrodynamic simulations and theory with results from dynamical modelling of realistic populations of impactors. We find that for an initially Earth-like atmosphere, impacts cause moderate atmospheric erosion with stochastic delivery of large asteroids, giving substantial growth (× 10) in a few ${{\ \rm per\ cent}}$ of cases. The exact change in atmosphere mass is inherently stochastic and dependent on the dynamics of the left-over planetesimals. We also consider the dependence on unknowns including the impactor volatile content, finding that the atmosphere is typically completely stripped by especially dry left-over planetesimals ($\lt 0.02 ~ {{\ \rm per\ cent}}$ volatiles). Remarkably, for a wide range of initial atmosphere masses and compositions, the atmosphere converges towards similar final masses and compositions, i.e. initially low-mass atmospheres grow, whereas massive atmospheres deplete. While the final properties are sensitive to the assumed impactor properties, the resulting atmosphere mass is close to that of current Earth. The exception to this is that a large initial atmosphere cannot be eroded to the current mass unless the atmosphere was initially primordial in composition.

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Saxena, Prabal, Lindy Elkins-Tanton, Noah Petro et Avi Mandell. « A model of the primordial lunar atmosphere ». Earth and Planetary Science Letters 474 (septembre 2017) : 198–205. http://dx.doi.org/10.1016/j.epsl.2017.06.031.

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Young, Edward D., Anat Shahar et Hilke E. Schlichting. « Earth shaped by primordial H2 atmospheres ». Nature 616, n^o 7956 (12 avril 2023) : 306–11. http://dx.doi.org/10.1038/s41586-023-05823-0.

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Libby-Roberts, Jessica E., Zachory K. Berta-Thompson, Hannah Diamond-Lowe, Michael A. Gully-Santiago, Jonathan M. Irwin, Eliza M. R. Kempton, Benjamin V. Rackham et al. « The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b : No Evidence for a Cloud-free Primordial Atmosphere and Constraints on Starspot Contamination ». Astronomical Journal 164, n^o 2 (19 juillet 2022) : 59. http://dx.doi.org/10.3847/1538-3881/ac75de.

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Abstract Orbiting an M dwarf 12 pc away, the transiting exoplanet GJ 1132b is a prime target for transmission spectroscopy. With a mass of 1.7 M ⊕ and radius of 1.1 R ⊕, GJ 1132b’s bulk density indicates that this planet is rocky. Yet with an equilibrium temperature of 580 K, GJ 1132b may still retain some semblance of an atmosphere. Understanding whether this atmosphere exists and its composition will be vital for understanding how the atmospheres of terrestrial planets orbiting M dwarfs evolve. We observe five transits of GJ 1132b with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). We find a featureless transmission spectrum from 1.1 to 1.7 μm, ruling out cloud-free atmospheres with metallicities <300× solar with >4.8σ confidence. We combine our WFC3 results with transit depths from TESS and archival broadband and spectroscopic observations to find a featureless spectrum across 0.7 to 4.5 μm. GJ 1132b therefore has a high mean molecular weight atmosphere, possesses a high-altitude aerosol layer, or has effectively no atmosphere. Higher-precision observations are required in order to differentiate between these possibilities. We explore the impact of hot and cold starspots on the observed transmission spectrum GJ 1132b, quantifying the amplitude of spot-induced transit depth features. Using a simple Poisson model, we estimate spot temperature contrasts, spot covering fractions, and spot sizes for GJ 1132. These limits, as well as the modeling framework, may be useful for future observations of GJ 1132b or other planets transiting similarly inactive M dwarfs.

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Micca Longo, Gaia, Luca Vialetto, Paola Diomede, Savino Longo et Vincenzo Laporta. « Plasma Modeling and Prebiotic Chemistry : A Review of the State-of-the-Art and Perspectives ». Molecules 26, n^o 12 (16 juin 2021) : 3663. http://dx.doi.org/10.3390/molecules26123663.

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We review the recent progress in the modeling of plasmas or ionized gases, with compositions compatible with that of primordial atmospheres. The plasma kinetics involves elementary processes by which free electrons ultimately activate weakly reactive molecules, such as carbon dioxide or methane, thereby potentially starting prebiotic reaction chains. These processes include electron–molecule reactions and energy exchanges between molecules. They are basic processes, for example, in the famous Miller-Urey experiment, and become relevant in any prebiotic scenario where the primordial atmosphere is significantly ionized by electrical activity, photoionization or meteor phenomena. The kinetics of plasma displays remarkable complexity due to the non-equilibrium features of the energy distributions involved. In particular, we argue that two concepts developed by the plasma modeling community, the electron velocity distribution function and the vibrational distribution function, may unlock much new information and provide insight into prebiotic processes initiated by electron–molecule collisions.

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Melosh, H. J., et A. M. Vickery. « Impact erosion of the primordial atmosphere of Mars ». Nature 338, n^o 6215 (avril 1989) : 487–89. http://dx.doi.org/10.1038/338487a0.

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NAKAZAWA, Kiyoshi, Hiroshi MIZUNO, Minoru SEKIYA et Chushiro HAYASHI. « Structure of the primordial atmosphere surrounding the early-earth. » Journal of geomagnetism and geoelectricity 37, n^o 8 (1985) : 781–99. http://dx.doi.org/10.5636/jgg.37.781.

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Scarsdale, Nicholas, Nicholas Wogan, Hannah R. Wakeford, Nicole L. Wallack, Natasha E. Batalha, Lili Alderson, Artyom Aguichine et al. « JWST COMPASS : The 3–5 μm Transmission Spectrum of the Super-Earth L 98-59 c ». Astronomical Journal 168, n^o 6 (19 novembre 2024) : 276. http://dx.doi.org/10.3847/1538-3881/ad73cf.

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Abstract We present a JWST Near-InfraRed Spectrograph (NIRSpec) transmission spectrum of the super-Earth exoplanet L 98-59 c. This small (R p = 1.385 ± 0.085R ⊕, M p = 2.22 ± 0.26 R ⊕), warm (T eq = 553 K) planet resides in a multiplanet system around a nearby, bright (J = 7.933) M3V star. We find that the transmission spectrum of L 98-59 c is featureless at the precision of our data. We achieve precisions of 22 ppm in NIRSpec G395H’s NRS1 detector and 36 ppm in the NRS2 detector at a resolution R ∼ 200 (30 pixel wide bins). At this level of precision, we are able rule out primordial H2–He atmospheres across a range of cloud pressure levels up to at least ∼0.1 mbar. By comparison to atmospheric forward models, we also rule out atmospheric metallicities below ∼300× solar at 3σ (or, equivalently, atmospheric mean molecular weights below ∼10 g mol−1). We also rule out pure methane atmospheres. The remaining scenarios that are compatible with our data include a planet with no atmosphere at all, or higher-mean-molecular-weight atmospheres, such as CO2- or H2O-rich atmospheres. This study adds to a growing body of evidence suggesting that planets ≲1.5 R ⊕ lack extended atmospheres.

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Ueda, Hisahiro, et Takazo Shibuya. « Composition of the Primordial Ocean Just after Its Formation : Constraints from the Reactions between the Primitive Crust and a Strongly Acidic, CO2-Rich Fluid at Elevated Temperatures and Pressures ». Minerals 11, n^o 4 (6 avril 2021) : 389. http://dx.doi.org/10.3390/min11040389.

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The Hadean was an enigmatic period in the Earth’s history when ocean formation and the emergence of life may have occurred. However, minimal geological evidence is left from this period. To understand the primordial ocean’s composition, we focused on the ocean’s formation processes from CO2- and HCl-bearing water vapor in the high-temperature atmosphere. When the temperature of the lower atmosphere fell below the critical point, high-temperature rain reached the ground surface. Then, hydrothermal reactions between the subcritical fluid and primordial crust started. Eventually, a liquid ocean emerged on the completely altered crust as the temperature decreased to approximately 25 °C. Here, we conducted two experiments and modeling to simulate the reactions of hypothetical primordial crustal rock (basalt or komatiite). The results indicate that the primordial ocean was mildly acidic and rich in CO2, Mg, and Ca relative to Na, irrespective of the rock type, which is different from the modern equivalents. Therefore, unlike the present seawater, the primordial seawater could have been carbonic, bitter, and harsh rather than salty.

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Misener, William, et Hilke E. Schlichting. « To cool is to keep : residual H/He atmospheres of super-Earths and sub-Neptunes ». Monthly Notices of the Royal Astronomical Society 503, n^o 4 (27 mars 2021) : 5658–74. http://dx.doi.org/10.1093/mnras/stab895.

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ABSTRACT Super-Earths and sub-Neptunes are commonly thought to have accreted hydrogen/helium envelopes, consisting of a few to ten percent of their total mass, from the primordial gas disc. Subsequently, hydrodynamic escape driven by core-powered mass-loss and/or photoevaporation likely stripped much of these primordial envelopes from the lower mass and closer-in planets to form the super-Earth population. In this work, we show that after undergoing core-powered mass-loss, some super-Earths can retain small residual H/He envelopes. This retention is possible because, for significantly depleted atmospheres, the density at the radiative–convective boundary drops sufficiently such that the cooling time-scale becomes shorter than the mass-loss time-scale. The residual envelope is therefore able to contract, terminating further mass-loss. Using analytic calculations and numerical simulations, we show that the mass of primordial H/He envelope retained as a fraction of the planet’s total mass, fret, increases with increasing planet mass, Mc, and decreases with increasing equilibrium temperature, Teq, scaling as $f_\mathrm{ret} \propto M_\mathrm{c}^{3/2} T_\mathrm{eq}^{-1/2} \exp {[M_\mathrm{c}^{3/4} T_\mathrm{eq}^{-1}]}$. fret varies from <10−8 to about 10−3 for typical super-Earth parameters. To first order, the exact amount of left-over H/He depends on the initial envelope mass, the planet mass, its equilibrium temperature, and the envelope’s opacity. These residual hydrogen envelopes reduce the atmosphere’s mean molecular weight compared to a purely secondary atmosphere, a signature observable by current and future facilities. These remnant atmospheres may, however, in many cases be vulnerable to long-term erosion by photoevaporation. Any residual hydrogen envelope likely plays an important role in the long-term physical evolution of super-Earths, including their geology and geochemistry.

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Kurosaki, Kenji, Yasunori Hori, Masahiro Ogihara et Masanobu Kunitomo. « Evolution of a Water-rich Atmosphere Formed by a Giant Impact on an Earth-sized Planet ». Astrophysical Journal 957, n^o 2 (31 octobre 2023) : 67. http://dx.doi.org/10.3847/1538-4357/acfe0a.

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Abstract The atmosphere of a terrestrial planet that is replenished with secondary gases should have accumulated hydrogen-rich gas from its protoplanetary disk. Although a giant impact blows off a large fraction of the primordial atmosphere of a terrestrial planet in the late formation stage, the remaining atmosphere can become water-rich via chemical reactions between hydrogen and vaporized core material. We find that a water-rich postimpact atmosphere forms when a basaltic or CI chondrite core is assumed. In contrast, little postimpact water is generated for an enstatite chondrite core. We investigate the X-ray- and UV-driven mass loss from an Earth-mass planet with an impact-induced multicomponent H2–He–H2O atmosphere for Gyr. We show that water is left in the atmosphere of an Earth-mass planet when the low flux of escaping hydrogen cannot drag water upward via collisions. For a water-dominated atmosphere to form, the atmospheric mass fraction of an Earth-mass planet with an oxidizing core after a giant impact must be less than a few times 0.1%. We also find that Earth-mass planets with water-dominated atmospheres can exist at semimajor axes ranging from a few times 0.1 au to a few au around a Sun-like star, depending on the mass-loss efficiency. Such planets are important targets for atmospheric characterization in the era of JWST. Our results indicate that efficient mixing between hydrogen and rocky components during giant impacts can play a role in the production of water in an Earth-mass planet.

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Trafton, L., S. A. Stern et G. R. Gladstone. « The Pluto-Charon system : The escape of charon's primordial atmosphere ». Icarus 74, n^o 1 (avril 1988) : 108–20. http://dx.doi.org/10.1016/0019-1035(88)90033-4.

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Howe, Alex R., Fred C. Adams et Michael R. Meyer. « Survival of Primordial Planetary Atmospheres : Photodissociation-driven Mass Loss ». Astrophysical Journal 894, n^o 2 (14 mai 2020) : 130. http://dx.doi.org/10.3847/1538-4357/ab620c.

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Kubyshkina, Daria, et Aline A. Vidotto. « How does the mass and activity history of the host star affect the population of low-mass planets ? » Monthly Notices of the Royal Astronomical Society 504, n^o 2 (27 mars 2021) : 2034–50. http://dx.doi.org/10.1093/mnras/stab897.

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ABSTRACT The evolution of the atmospheres of low- and intermediate-mass planets is strongly connected to the physical properties of their host stars. The types and the past activities of planet-hosting stars can, therefore, affect the overall planetary population. In this paper, we perform a comparative study of sub-Neptune-like planets orbiting stars of different masses and different evolutionary histories. We discuss the general patterns of the evolved population as a function of parameters and environments of planets. As a model of the atmospheric evolution, we employ the own framework combining planetary evolution in Modules for Experiments in Stellar Astrophysics (mesa) with the realistic prescription of the escape of hydrogen-dominated atmospheres. We find that the final populations look qualitatively similar in terms of the atmospheres survival around different stars, but qualitatively different, with this difference accentuated for planets orbiting more massive stars. We show that a planet has larger chances of keeping its primordial atmosphere in the habitable zone of a solar-mass star compared to M or K dwarfs and if it starts the evolution having a relatively compact envelope. We also address the problem of the uncertain initial temperatures (luminosities) of planets and show that this issue is only of particular importance for planets exposed to extreme atmospheric mass losses.

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Atri, Dimitra, et Shane R. Carberry Mogan. « Stellar flares versus luminosity : XUV-induced atmospheric escape and planetary habitability ». Monthly Notices of the Royal Astronomical Society : Letters 500, n^o 1 (9 novembre 2020) : L1—L5. http://dx.doi.org/10.1093/mnrasl/slaa166.

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ABSTRACT Space weather plays an important role in the evolution of planetary atmospheres. Observations have shown that stellar flares emit energy in a wide energy range (1030–1038 erg), a fraction of which lies in X-rays and extreme ultraviolet (XUV). These flares heat the upper atmosphere of a planet, leading to increased escape rates, and can result in atmospheric erosion over a period of time. Observations also suggest that primordial terrestrial planets can accrete voluminous H/He envelopes. Stellar radiation can erode these protoatmospheres over time, and the extent of this erosion has implications for the planet’s habitability. We use the energy-limited equation to calculate hydrodynamic escape rates from these protoatmospheres irradiated by XUV stellar flares and luminosity. We use the flare frequency distribution of 492 FGKM stars observed with TESS to estimate atmospheric loss in habitable zone planets. We find that for most stars, luminosity-induced escape is the main loss mechanism, with a minor contribution from flares. However, flares dominate the loss mechanism of ∼20 per cent M4–M10 stars. M0–M4 stars are most likely to completely erode both their proto- and secondary atmospheres, and M4–M10 are least likely to erode secondary atmospheres. We discuss the implications of these results on planetary habitability.

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Lentz, Eric J., Peter H. Hauschildt, Jason P. Aufdenberg et Ed Baron. « Model atmospheres of massive zero-metallicity stars ». Symposium - International Astronomical Union 212 (2003) : 416–17. http://dx.doi.org/10.1017/s0074180900212552.

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We have calculated detailed, fully non-LTE, model atomospheres for massive zero-metal stars. We find the atmospheres of massive primordial stars become unbound due to radiation pressure on lines and continua over a much larger fraction of their evolution than previously expected.

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Cannon, Kevin M., Stephen W. Parman et John F. Mustard. « Primordial clays on Mars formed beneath a steam or supercritical atmosphere ». Nature 552, n^o 7683 (décembre 2017) : 88–91. http://dx.doi.org/10.1038/nature24657.

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Tian, Meng, et Kevin Heng. « Atmospheric Chemistry of Secondary and Hybrid Atmospheres of Super Earths and Sub-Neptunes ». Astrophysical Journal 963, n^o 2 (1 mars 2024) : 157. http://dx.doi.org/10.3847/1538-4357/ad217c.

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Abstract The atmospheres of small exoplanets likely derive from a combination of geochemical outgassing and primordial gases left over from formation. Secondary atmospheres, such as those of Earth, Mars, and Venus, are sourced by outgassing. Persistent outgassing into long-lived, primordial, hydrogen–helium envelopes produces hybrid atmospheres of which there are no examples in the solar system. We construct a unified theoretical framework for calculating the outgassing chemistry of both secondary and hybrid atmospheres, where the input parameters are the surface pressure, oxidation, and sulfidation states of the mantle, as well as the primordial atmospheric hydrogen, helium, and nitrogen content. Nonideal gases (quantified by the fugacity coefficient) and nonideal mixing of gaseous components (quantified by the activity coefficient) are considered. Both secondary and hybrid atmospheres exhibit a rich diversity of chemistries, including hydrogen-dominated atmospheres. The abundance ratio of carbon dioxide to carbon monoxide serves as a powerful diagnostic for the oxygen fugacity of the mantle, which may conceivably be constrained by James Webb Space Telescope spectra in the near future. Methane-dominated atmospheres are difficult to produce and require specific conditions: atmospheric surface pressures exceeding ∼10 bar, a reduced (poorly oxidized) mantle, and diminished magma temperatures (compared to modern Earth). Future work should include photochemistry in these calculations and clarify the general role of atmospheric escape. Exoplanet science should quantify the relationship between the mass and oxygen fugacity for a sample of super Earths and sub-Neptunes; such an empirical relationship already exists for solar system bodies.

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Glover, Simon, et Daniel Wolf Savin. « cooling in primordial gas ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 364, n^o 1848 (20 septembre 2006) : 3107–12. http://dx.doi.org/10.1098/rsta.2006.1867.

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Simulations of the thermal and dynamical evolution of primordial gas typically focus on the role played by H 2 cooling. H 2 is the dominant coolant in low-density primordial gas and it is usually assumed that it remains dominant at high densities. However, H 2 is not an effective coolant at high densities, owing to the low critical density at which it reaches local thermodynamic equilibrium and to the large opacities that develop in its emission lines. It is therefore important to quantify the contribution made to the cooling rate by emission from the other molecules and ions present in the gas. A particularly interesting candidate is the ion, which is known to be an effective coolant at high densities in planetary atmospheres. In this paper, we present results from simulations of the thermal and chemical evolution of gravitationally collapsing primordial gas, which include a detailed treatment of chemistry and an approximate treatment of cooling. We show that in most cases, the contribution from is too small to be important, but if a sufficiently strong ionizing background is present, then cooling may become significant.

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Spite, M., P. Bonifacio, F. Spite, E. Caffau, L. Sbordone et A. J. Gallagher. « Be and O in the ultra metal-poor dwarf 2MASS J18082002-5104378 : the Be–O correlation ». Astronomy & ; Astrophysics 624 (avril 2019) : A44. http://dx.doi.org/10.1051/0004-6361/201834741.

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Context. Measurable amounts of Be could have been synthesised primordially if the Universe were non-homogeneous or in the presence of late decaying relic particles. Aims. We investigate the Be abundance in the extremely metal-poor star 2MASS J1808-5104 ([Fe/H] = −3.84) with the aim of constraining inhomogeneities or the presence of late decaying particles. Methods. High resolution, high signal-to-noise ratio (S/N) UV spectra were acquired at ESO with the Kueyen 8.2 m telescope and the UVES spectrograph. Abundances were derived using several model atmospheres and spectral synthesis code. Results. We measured log(Be/H) = −14.3 from a spectrum synthesis of the region of the Be line. Using a conservative approach, however we adopted an upper limit two times higher, i.e. log(Be/H) < −14.0. We measured the O abundance from UV–OH lines and find [O/H] = −3.46 after a 3D correction. Conclusions. Our observation reinforces the existing upper limit on primordial Be. There is no observational indication for a primordial production of 9Be. This places strong constraints on the properties of putative relic particles. This result also supports the hypothesis of a homogeneous Universe, at the time of nucleosynthesis. Surprisingly, our upper limit of the Be abundance is well below the Be measurements in stars of similar [O/H]. This may be evidence that the Be–O relation breaks down in the early Galaxy, perhaps due to the escape of spallation products from the gas clouds in which stars such as 2MASS J1808-5104 have formed.

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Mizuno, Hiroshi, et Kiyoshi Nakazawa. « Chapter 22. Primordial Atmosphere Surrounding a Protoplanet and Formation of Jovian Planets ». Progress of Theoretical Physics Supplement 96 (1988) : 266–73. http://dx.doi.org/10.1143/ptps.96.266.

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Yalinewich, Almog, et Matthew E. Caplan. « Crater morphology of primordial black hole impacts ». Monthly Notices of the Royal Astronomical Society : Letters 505, n^o 1 (10 juin 2021) : L115—L119. http://dx.doi.org/10.1093/mnrasl/slab063.

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ABSTRACT In this work, we propose a novel campaign for constraining relativistically compact massive compact halo object (MACHO) dark matter, such as primordial black holes (PBHs), using the Moon as a detector. PBHs of about 1019 to 1022 g may be sufficiently abundant to have collided with the Moon in the history of the Solar system. We show that the crater profiles of a PBH collision differ from traditional impactors and may be detectable in high-resolution lunar surface scans now available. Any candidates may serve as sites for in situ measurements to identify high-pressure phases of matter which may have formed near the PBH during the encounter. While we primarily consider PBH dark matter, the discussion generalizes to the entire family of MACHO candidates with relativistic compactness. Moreover, we focus on the Moon since it has been studied well, but the same principles can be applied to other rocky bodies in our Solar system without an atmosphere.

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Zhou, Li, Bo Ma, Yonghao Wang et Yinan Zhu. « Hubble WFC3 Spectroscopy of the Rocky Planet L 98–59 b : No Evidence for a Cloud-free Primordial Atmosphere ». Astronomical Journal 164, n^o 5 (19 octobre 2022) : 203. http://dx.doi.org/10.3847/1538-3881/ac8fe9.

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Abstract We are using archived data from HST of transiting exoplanet L 98-59 b to place constraints on its potentially hot atmosphere. We analyze the data from five transit visits and extract the final combined transmission spectrum using Iraclis. Then we use the inverse atmospheric retrieval code TauREx to analyze the combined transmission spectrum. There is a weak absorption feature near 1.40 μm and 1.55 μm in the transmission spectrum, which can be modeled by a cloudy atmosphere with abundant hydrogen cyanide (HCN). However, the unrealistically high abundance of HCN derived cannot be explained by any equilibrium chemical model with reasonable assumptions. Thus, the likeliest scenario is that L 98-59 b has a flat, featureless transmission spectrum in the WFC3/G141 bandpass due to a thin atmosphere with high mean molecular weight, an atmosphere with an opaque aerosol layer, or no atmosphere, and it is very unlikely for L 98-59 b to have a clear hydrogen-dominated primary atmosphere. Due to the narrow wavelength coverage and low spectral resolution of HST/WFC3 G141 grism observation, we cannot tell these different scenarios apart. Our simulation shows future higher precision measurements over wider wavelengths from the James Webb Space Telescope can be used to better characterize the planetary atmosphere of L 98-59 b.

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Micca Longo, Gaia, et Savino Longo. « The role of primordial atmosphere composition in organic matter delivery to early Earth ». Rendiconti Lincei. Scienze Fisiche e Naturali 31, n^o 1 (10 février 2020) : 53–64. http://dx.doi.org/10.1007/s12210-020-00878-x.

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Howk, J. Christopher. « Interstellar Lithium as a probe of the primordial abundance ». Proceedings of the International Astronomical Union 5, S268 (novembre 2009) : 335–36. http://dx.doi.org/10.1017/s1743921310004357.

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AbstractThe cosmic abundance of lithium continues to represent a conundrum, as predictions from BBN theory are inconsistent with measurements in the atmospheres of the lowest-metallicity stars. While there are worries that modifications of the stellar Li abundances may play a role in this discrepancy, no satisfactory solution has yet been found. We suggest an alternate approach to studying the cosmic abundance of Li: measurements of interstellar gas-phase Li in low-metallicity environments.

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Dorfi, Ernst A., et Florian Ragossnig. « Interaction of solid bodies with atmospheres of protoplanets ». Proceedings of the International Astronomical Union 14, S345 (août 2018) : 351–52. http://dx.doi.org/10.1017/s1743921319001996.

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AbstractDuring the early stages of planet formation accretion of small bodies add mass to the planet and deposit their energy kinetic energy. Caused by frictional heating and/or large stagnation pressures within the dense and extended atmospheres most of the in-falling bodies get destroyed by melting or break-up before they impact on the planet’s surface. The energy is added to the atmospheric layers rather than heating the planet directly. These processes can significantly alter the physical properties of protoplanets before they are exposed with their primordial atmospheres to the early stellar source when the protoplanetary disk becomes evaporated.

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Jaupart, Etienne, Sebatien Charnoz et Manuel Moreira. « Primordial atmosphere incorporation in planetary embryos and the origin of Neon in terrestrial planets ». Icarus 293 (septembre 2017) : 199–205. http://dx.doi.org/10.1016/j.icarus.2017.04.022.

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Molaverdikhani, K., Ch Helling, B. W. P. Lew, R. J. MacDonald, D. Samra, N. Iro, P. Woitke et V. Parmentier. « Understanding the atmospheric properties and chemical composition of the ultra-hot Jupiter HAT-P-7b ». Astronomy & ; Astrophysics 635 (mars 2020) : A31. http://dx.doi.org/10.1051/0004-6361/201937044.

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Aims. The atmospheres of ultra-hot Jupiters (UHJs) are commonly considered to be at thermochemical equilibrium. We aim to provide disequilibrium chemistry maps for a global understanding of the chemistry in the atmosphere of HAT-P-7b and assess the importance of disequilibrium chemistry on UHJs. Methods. We applied a hierarchical modeling approach using 97 1D atmospheric profiles from a 3D general circulation model of HAT-P-7b. For each atmospheric 1D profile, we evaluated our kinetic cloud formation model consistently with the local gas-phase composition in chemical equilibrium. This served as input to study the quenching of dominating CHNO-binding molecules. We evaluated quenching results from a zeroth-order approximation in comparison to a kinetic gas-phase approach. Results. We find that the zeroth-order approach of estimating quenching points agrees well with the full gas-kinetic modeling results. However, it underestimates the quenching levels by about one order of magnitude at high temperatures. Chemical disequilibrium has the greatest effect on the nightside and morning abundance of species such as H, H2O, CH4, CO2, HCN, and all CnHm molecules; heavier CnHm molecules are more affected by disequilibrium processes. The CO abundance, however, is affected only marginally. While dayside abundances also notably change, those around the evening terminator of HAT-P-7b are the least affected by disequilibrium processes. The latter finding may partially explain the consistency of observed transmission spectra of UHJs with atmospheres in thermochemical equilibrium. Photochemistry only negligibly affects molecular abundances and quenching levels. Conclusions. In general, the quenching points of the atmosphere of HAT-P-7b are at much lower pressures than in the cooler hot-jupiters. We propose several avenues to determining the effect of disequilibrium processes on UHJs that are in general based on abundance and opacity measurements at different local times. It remains a challenge to completely disentangle this from the chemical effects of clouds and that of a primordial nonsolar abundance.

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Malaney, Robert A. « Lithium-6 Nucleosynthesis in the ISM ». Highlights of Astronomy 10 (1995) : 465–66. http://dx.doi.org/10.1017/s1539299600011771.

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The nucleosynthesis of 6Li in the galaxy has become of considerable interest in the past year. This is largely because of the exciting developments relating to the first detection of this isotope outside of our own solar system. Not only has 6Li been recently detected in the atmospheres of halo dwarfs [1-2], but also in the local interstellar medium (ISM) [3-4].It is well known that knowledge of the primordial abundance of the lithium isotopes has important ramifications for cosmology, through the constraints they impose on standard big bang nucleosynthesis (SBBN) [5], and those imposed on non-standard primordial nucleosynthesis models. Since a complete understanding of the galactic evolution of the lithium isotopes is a prerequisite to unambiguously determining their primordial abundance, a thorough interpretation of the new 6Li data in the context of chemical evolution models cannot be overstated.

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Oberhausen, E. « Natürliche Strahlenexposition einschließlich Radon ». Nuklearmedizin 30, S 05 (novembre 1991) : 220–25. http://dx.doi.org/10.1055/s-0038-1629578.

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ZusammenfassungDie natürliche Strahlenexposition des Menschen wird durch die kosmische Strahlung und die in der Erdrinde vorhandenen primordialen Radionuklide verursacht. Da es durch die Wechselwirkung der kosmischen Strahlung in der Atmosphäre auch zur Bildung von Radionukliden kommt, werden durch beide Komponenten sowohl eine externe als auch eine interne Strahlenexposition durch Aufnahme von Radionukliden mit der Nahrungverursacht. Die externe Strahlenexposition nimmt wegen der kosmischen Strahlung mit der Höhe über dem Meeresspiegel zu und ist wegen der primordialen Radionuklide abhängig von deren unterschiedlicher Konzentration in der Erdrinde. Diese unterschiedliche Konzentration ist auch die wichtigste Ausgangsgröße für die interne Strahlenexposition. Das in der Uran-Radiumreihe vorhandene radioaktive Edelgas Radon und seine kurzlebigen Folgeprodukte reichern sich aus dem Untergrund in unseren Wohnungen an und werden dadurch zu einem wesentlichen Faktor in der natürlichen Strahlenexposition.

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Ferus, Martin, Fabio Pietrucci, Antonino Marco Saitta, Antonín Knížek, Petr Kubelík, Ondřej Ivanek, Violetta Shestivska et Svatopluk Civiš. « Formation of nucleobases in a Miller–Urey reducing atmosphere ». Proceedings of the National Academy of Sciences 114, n^o 17 (10 avril 2017) : 4306–11. http://dx.doi.org/10.1073/pnas.1700010114.

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The Miller–Urey experiments pioneered modern research on the molecular origins of life, but their actual relevance in this field was later questioned because the gas mixture used in their research is considered too reducing with respect to the most accepted hypotheses for the conditions on primordial Earth. In particular, the production of only amino acids has been taken as evidence of the limited relevance of the results. Here, we report an experimental work, combined with state-of-the-art computational methods, in which both electric discharge and laser-driven plasma impact simulations were carried out in a reducing atmosphere containing NH3 + CO. We show that RNA nucleobases are synthesized in these experiments, strongly supporting the possibility of the emergence of biologically relevant molecules in a reducing atmosphere. The reconstructed synthetic pathways indicate that small radicals and formamide play a crucial role, in agreement with a number of recent experimental and theoretical results.

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Swindle, T. D., et J. H. Jones. « The xenon isotopic composition of the primordial Martian atmosphere : Contributions from solar and fission components ». Journal of Geophysical Research : Planets 102, E1 (1 janvier 1997) : 1671–78. http://dx.doi.org/10.1029/96je03110.

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Biersteker, John B., et Hilke E. Schlichting. « Losing oceans : The effects of composition on the thermal component of impact-driven atmospheric loss ». Monthly Notices of the Royal Astronomical Society 501, n^o 1 (26 novembre 2020) : 587–95. http://dx.doi.org/10.1093/mnras/staa3614.

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ABSTRACT The formation of the Solar system’s terrestrial planets concluded with a period of giant impacts. Previous works examining the volatile loss caused by the impact shock in the moon-forming impact find atmospheric losses of at most 20–30 per cent and essentially no loss of oceans. However, giant impacts also result in thermal heating, which can lead to significant atmospheric escape via a Parker-type wind. Here we show that H2O and other high-mean molecular weight outgassed species can be efficiently lost through this thermal wind if present in a hydrogen-dominated atmosphere, substantially altering the final volatile inventory of terrestrial planets. We demonstrate that a giant impact during terrestrial planet formation can remove several Earth oceans’ worth of H2O, and other heavier volatile species, together with a primordial hydrogen-dominated atmosphere. These results may offer an explanation for the observed depletion in Earth’s light noble gas budget and for its depleted xenon inventory, which suggest that Earth underwent significant atmospheric loss by the end of its accretion. Because planetary embryos are massive enough to accrete primordial hydrogen envelopes and because giant impacts are stochastic and occur concurrently with other early atmospheric evolutionary processes, our results suggest a wide diversity in terrestrial planet volatile budgets.

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Gräfener, Götz, et Wolf-Rainer Hamann. « Wolf-Rayet Wind Models from Hydrodynamic Model Atmospheres ». Proceedings of the International Astronomical Union 3, S250 (décembre 2007) : 63–70. http://dx.doi.org/10.1017/s1743921308020346.

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AbstractWe present a parameter study of WR-type mass loss, based on the PoWR hydrodynamic model atmospheres. These new models imply that optically thick WR-type winds are generally formed close to the Eddington limit. This is demonstrated for the case of hydrogen rich WNL stars, which turn out to be extremely massive, luminous stars with progenitor masses above ≈ 80 M⊙. We investigate the dependence of WR-type mass loss on various stellar parameters, including the metallicity Z. The results depend strongly on the L/M ratio, the stellar temperature T*, and the assumed wind clumping. For high L/M ratios, strong WR-type winds can be maintained down to very low Z. Even for primordial massive stars we predict considerable mass loss if their surfaces are self-enriched by primary elements.

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Schroeder I, Isaac R. H. G., Kathrin Altwegg, Hans Balsiger, Jean-Jacques Berthelier, Johan De Keyser, Björn Fiethe, Stephen A. Fuselier et al. « 16O/18O ratio in water in the coma of comet 67P/Churyumov-Gerasimenko measured with the Rosetta/ROSINA double-focusing mass spectrometer ». Astronomy & ; Astrophysics 630 (20 septembre 2019) : A29. http://dx.doi.org/10.1051/0004-6361/201833806.

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The European Space Agency spacecraft Rosetta accompanied the Jupiter-family comet 67P/Churyumov-Gerasimenko for over 2 yr along its trajectory through the inner solar system. Between 2014 and 2016, it performed almost continuous in situ measurements of the comet’s gaseous atmosphere in close proximity to its nucleus. In this study, the 16O/18O ratio of H2O in the coma of 67P/Churyumov-Gerasimenko, as measured by the ROSINA DFMS mass spectrometer onboard Rosetta, was determined from the ratio of H216O/H218O and 16OH/18OH. The value of 445 ± 35 represents an ~11% enrichment of 18O compared with the terrestrial ratio of 498.7 ± 0.1. This cometary value is consistent with the comet containing primordial water, in accordance with leading self-shielding models. These models predict primordial water to be between 5 and 20% enriched in heavier oxygen isotopes compared to terrestrial water.

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Afshordi, N., R. B. Mann et R. Pourhasan. « A holographic big bang ? » International Journal of Modern Physics D 24, n^o 12 (octobre 2015) : 1544029. http://dx.doi.org/10.1142/s0218271815440290.

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We present a cosmological model in which the Universe emerges out of the collapse of a five-dimensional (5D) star as a spherical three-brane. The initial singularity of the big bang becomes hidden behind a causal horizon. Near scale-invariant primordial curvature perturbations can be induced on the brane via a thermal atmosphere that is in equilibrium with the brane, circumventing the need for a separate inflationary process and providing an important test of the model.

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Sasaki, Sho, et Kiyoshi Nakazawa. « Origin of isotopic fractionation of terrestrial Xe : hydrodynamic fractionation during escape of the primordial H2He atmosphere ». Earth and Planetary Science Letters 89, n^o 3-4 (août 1988) : 323–34. http://dx.doi.org/10.1016/0012-821x(88)90120-3.

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Gibson, Carl H. « Turbulence in the Ocean, Atmosphere, Galaxy, and Universe ». Applied Mechanics Reviews 49, n^o 5 (1 mai 1996) : 299–315. http://dx.doi.org/10.1115/1.3101929.

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Flows in natural bodies of fluid often become turbulent, with eddy-like motions dominated by inertial-vortex forces. Buoyancy, Coriolis, viscous, self-gravitational, electromagnetic, and other force constraints produce a complex phase space of wave-like hydrodynamic states that interact with turbulence eddies, masquerade as turbulence, and preserve information about previous hydrodynamic states as fossil turbulence. Evidence from the ocean, atmosphere, galaxy and universe are compared with universal similarity hypotheses of Kolmogorov (1941, 1962) for turbulence velocity u, and extensions to scalar fields θ like temperature mixed by turbulence. Universal u and θ spectra of natural flows can be inferred from laboratory and computer simulations with satisfactory accuracy, but higher order spectra and the intermittency constant u of the third Kolmogorov hypothesis (1962) require measurements at the much larger Reynolds numbers found only in nature. Information about previous hydrodynamic states is preserved by Schwarz viscous and turbulence lengths and masses of self-gravitating condensates (rarely by the classical Jeans length and mass), as it is by Ozmidov, Hopfinger and Fernando scales in hydrophysical fields of the ocean and atmosphere. Viscous-gravitational formation occurred 104-105 y after the Big Bang for supercluster, cluster, and then galaxy masses of the plasma, producing the first turbulence. Condensation after plasma neutralization of the H-4He gas was to a primordial fog of sub-solar particles that persists today in galactic halos as dark matter. These gradually formed all stars, star clusters, etc (humans!) within.

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Mukhopadhyay, Sujoy, et Rita Parai. « Noble Gases : A Record of Earth's Evolution and Mantle Dynamics ». Annual Review of Earth and Planetary Sciences 47, n^o 1 (30 mai 2019) : 389–419. http://dx.doi.org/10.1146/annurev-earth-053018-060238.

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Noble gases have played a key role in our understanding of the origin of Earth's volatiles, mantle structure, and long-term degassing of the mantle. Here we synthesize new insights into these topics gained from high-precision noble gas data. Our analysis reveals new constraints on the origin of the terrestrial atmosphere, the presence of nebular neon but chondritic krypton and xenon in the mantle, and a memory of multiple giant impacts during accretion. Furthermore, the reservoir supplying primordial noble gases to plumes appears to be distinct from the mid-ocean ridge basalt (MORB) reservoir since at least 4.45 Ga. While differences between the MORB mantle and plume mantle cannot be explained solely by recycling of atmospheric volatiles, injection and incorporation of atmospheric-derived noble gases into both mantle reservoirs occurred over Earth history. In the MORB mantle, the atmospheric-derived noble gases are observed to be heterogeneously distributed, reflecting inefficient mixing even within the vigorously convecting MORB mantle. ▪ Primordial noble gases in the atmosphere were largely derived from planetesimals delivered after the Moon-forming giant impact. ▪ Heterogeneities dating back to Earth's accretion are preserved in the present-day mantle. ▪ Mid-ocean ridge basalts and plume xenon isotopic ratios cannot be related by differential degassing or differential incorporation of recycled atmospheric volatiles. ▪ Differences in mid-ocean ridge basalts and plume radiogenic helium, neon, and argon ratios can be explained through the lens of differential long-term degassing.

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Anderson, Don L. « A model to explain the various paradoxes associated with mantle noble gas geochemistry ». Proceedings of the National Academy of Sciences 95, n^o 16 (4 août 1998) : 9087–92. http://dx.doi.org/10.1073/pnas.95.16.9087.

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As a result of an energetic accretion, the Earth is a volatile-poor and strongly differentiated planet. The volatile elements can be accounted for by a late veneer (≈1% of total mass of the Earth). The incompatible elements are strongly concentrated into the exosphere (atmosphere, oceans, sediments, and crust) and upper mantle. Recent geochemical models invoke a large primordial undegassed reservoir with chondritic abundances of uranium and helium, which is clearly at odds with mass and energy balance calculations. The basic assumption behind these models is that excess “primordial” 3He is responsible for 3He/4He ratios higher than the average for midocean ridge basalts. The evidence however favors depletion of 3He and excessive depletion of 4He and, therefore, favors a refractory, residual (low U, Th) source Petrological processes such as melt-crystal and melt-gas separation fractionate helium from U and Th and, with time, generate inhomogeneities in the 3He/4He ratio. A self-consistent model for noble gases involves a gas-poor planet with trapping of CO2 and noble gases in the shallow mantle. Such trapped gases are released by later tectonic and magmatic processes. Most of the mantle was depleted and degassed during the accretion process. High 3He/4He gases are viewed as products of ancient gas exsolution stored in low U environments, rather than products of primordial reservoirs.

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Xing, Lei, Dongdong Yan et Jianheng Guo. « The Mass Fractionation of Helium in the Escaping Atmosphere of HD 209458b* ». Astrophysical Journal 953, n^o 2 (1 août 2023) : 166. http://dx.doi.org/10.3847/1538-4357/ace43f.

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Abstract The absorption signals of metastable He in HD 209458b and several other exoplanets can be explained via an escaping atmosphere model with a subsolar He/H ratio. The low abundance of helium can be a result of planet formation if there is a small amount of helium in their primordial atmosphere. However, another possibility is that the low He/H ratio is caused by the process of mass fractionation of helium in the atmosphere. In order to investigate the effect of fractionation in the hydrogen-helium atmosphere, we developed a self-consistent multi-fluid 1D hydrodynamic model based on the well-known open-source MHD code PLUTO. Our simulations show that a lower He/H ratio can be produced spontaneously in the multi-fluid model. We further modeled the transmission spectra of He 10830 lines for HD 209458b in a broad parameter space. The transmission spectrum of the observation can be fitted in the condition of 1.80 times the X-ray and extreme-ultraviolet flux of the quiet Sun. Meanwhile, the ratio of the escaping flux of helium to hydrogen, F He/F H, is 0.039. Our results indicate that the mass fractionation of helium to hydrogen can naturally interpret the low He/H ratio required by the observation. Thus, in the escaping atmosphere of HD 209458b, decreasing the abundance of helium in the atmosphere is not needed even if its He abundance is similar to that of the Sun. The simulation presented in this work hints that in the escaping atmosphere, mass fractionation can also occur on other exoplanets, which needs to be explored further.

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Ávila, Patricio Javier, Tommaso Grassi, Stefano Bovino, Andrea Chiavassa, Barbara Ercolano, Sebastian Oscar Danielache et Eugenio Simoncini. « Presence of water on exomoons orbiting free-floating planets : a case study ». International Journal of Astrobiology 20, n^o 4 (8 juin 2021) : 300–311. http://dx.doi.org/10.1017/s1473550421000173.

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AbstractA free-floating planet (FFP) is a planetary-mass object that orbits around a non-stellar massive object (e.g. a brown dwarf) or around the Galactic Centre. The presence of exomoons orbiting FFPs has been theoretically predicted by several models. Under specific conditions, these moons are able to retain an atmosphere capable of ensuring the long-term thermal stability of liquid water on their surface. We model this environment with a one-dimensional radiative-convective code coupled to a gas-phase chemical network including cosmic rays and ion-neutral reactions. We find that, under specific conditions and assuming stable orbital parameters over time, liquid water can be formed on the surface of the exomoon. The final amount of water for an Earth-mass exomoon is smaller than the amount of water in Earth oceans, but enough to host the potential development of primordial life. The chemical equilibrium time-scale is controlled by cosmic rays, the main ionization driver in our model of the exomoon atmosphere.

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Kubyshkina, D., L. Fossati, A. J. Mustill, P. E. Cubillos, M. B. Davies, N. V. Erkaev, C. P. Johnstone et al. « The Kepler-11 system : evolution of the stellar high-energy emission and initial planetary atmospheric mass fractions ». Astronomy & ; Astrophysics 632 (29 novembre 2019) : A65. http://dx.doi.org/10.1051/0004-6361/201936581.

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The atmospheres of close-in planets are strongly influenced by mass loss driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of the host star, particularly during the early stages of evolution. We recently developed a framework to exploit this connection and enable us to recover the past evolution of the stellar high-energy emission from the present-day properties of its planets, if the latter retain some remnants of their primordial hydrogen-dominated atmospheres. Furthermore, the framework can also provide constraints on planetary initial atmospheric mass fractions. The constraints on the output parameters improve when more planets can be simultaneously analysed. This makes the Kepler-11 system, which hosts six planets with bulk densities between 0.66 and 2.45 g cm−3, an ideal target. Our results indicate that the star has likely evolved as a slow rotator (slower than 85% of the stars with similar masses), corresponding to a high-energy emission at 150 Myr of between 1 and 10 times that of the current Sun. We also constrain the initial atmospheric mass fractions for the planets, obtaining a lower limit of 4.1% for planet c, a range of 3.7–5.3% for planet d, a range of 11.1–14% for planet e, a range of 1–15.6% for planet f, and a range of 4.7–8.7% for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range remains poorly constrained. Our framework also suggests slightly higher masses for planets b, c, and f than have been suggested based on transit timing variation measurements. We coupled our results with published planet atmosphere accretion models to obtain a temperature (at 0.25 AU, the location of planet f) and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although these results may be affected by inconsistencies in the adopted system parameters. This work shows that our framework is capable of constraining important properties of planet formation models.

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Chakrabarty, Aritra, et Gijs D. Mulders. « Where Are the Water Worlds ? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution ». Astrophysical Journal 966, n^o 2 (1 mai 2024) : 185. http://dx.doi.org/10.3847/1538-4357/ad3802.

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Abstract Planet formation models suggest that the small exoplanets that migrate from beyond the snowline of the protoplanetary disk likely contain water-ice-rich cores (∼50% by mass), also known as water worlds. While the observed radius valley of the Kepler planets is well explained by the atmospheric dichotomy of the rocky planets, precise measurements of the mass and radius of the transiting planets hint at the existence of these water worlds. However, observations cannot confirm the core compositions of those planets, owing to the degeneracy between the density of a bare water-ice-rich planet and the bulk density of a rocky planet with a thin atmosphere. We combine different formation models from the Genesis library with atmospheric escape models, such as photoevaporation and impact stripping, to simulate planetary systems consistent with the observed radius valley. We then explore the possibility of water worlds being present in the currently observed sample by comparing them with simulated planets in the mass–radius–orbital period space. We find that the migration models suggest ≳10% and ≳20% of the bare planets, i.e., planets without primordial H/He atmospheres, to be water-ice-rich around G- and M-type host stars, respectively, consistent with the mass–radius distributions of the observed planets. However, most of the water worlds are predicted to be outside a period of 10 days. A unique identification of water worlds through radial velocity and transmission spectroscopy is likely to be more successful when targeting such planets with longer orbital periods.

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Rivera Quintero, Rosario, et Verónica Useche Ospinal. « Creating an atmosphere of enthusiasm and motivation in the classroom ». Revista Sapientía 10, n^o 20 (16 juillet 2021) : 34–40. http://dx.doi.org/10.54278/sapientia.v10i20.56.

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En el ámbito educativo actual, la figura del docente está siendo cada vez más desestimada por parte de los mismos estudiantes, lo cual ha ido generando una serie de factores que hacen que ellos ya no se sientan motivados por aprender o encuentren diversas excusas para no querer apropiarse de sus conocimientos. A través de éste artículo, se pretende concientizar, animar y ayudar al maestro a apropiarse de su rol y ejercerlo de tal forma que pueda ser un canal que estimule el aprendizaje en sus estudiantes sin que ellos se sientan presionados ni obligados. Los tres componentes mencionados en el artículo y que ayudarán a abordar este tema son: creatividad, innovación y estimulación intelectual. Si bien en el proceso de formación, éstos deben ser desarrollados de forma conectada, muchos los ven como factores aislados entre sí o no interconectados. La correlación que estos tres elementos poseen es primordial en el manejo y organización al interior de las aulas, ya que tiene como fin interesar a los aprendices a ser más conscientes y a involucrarse más en su propio aprendizaje, sintiéndose responsables de cumplir las metas u objetivos propuestos y estimulando sus capacidades en el logro de los mismos. Por otro lado, reconocer la importancia del rol del docente, su pasión por enseñar y formar, son puntos claves para la creación de ambientes motivacionales y entusiastas, ya que esto conlleva a que los estudiantes asimilen y se interesen por aprender de manera más natural y fresca sin dejar de lado la exigencia y excelencia en cada uno de los procesos.

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