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1
Unterborn, Cayman T., Bradford J. Foley, Steven J. Desch, Patrick A. Young, Gregory Vance, Lee Chiffelle et Stephen R. Kane. « Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets Can Support Temperate Climates ». Astrophysical Journal Letters 930, no 1 (1 mai 2022) : L6. http://dx.doi.org/10.3847/2041-8213/ac6596.
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Abstract The ideal exoplanets to search for life are those within a star’s habitable zone. However, even within the habitable zone, planets can still develop uninhabitable climate states. Sustaining a temperate climate over geologic (∼gigayear) timescales requires a planet to contain sufficient internal energy to power a planetary-scale carbon cycle. A major component of a rocky planet’s energy budget is the heat produced by the decay of radioactive elements, especially 40K, 232Th, 235U, and 238U. As the planet ages and these elements decay, this radiogenic energy source dwindles. Here we estimate the probability distribution of the amount of these heat-producing elements that enter into rocky exoplanets through Galactic history by combining the system-to-system variation seen in stellar abundance data with the results from Galactic chemical evolution models. From this, we perform Monte Carlo thermal evolution models that maximize the mantle cooling rate, thus allowing us to create a pessimistic estimate of lifetime a rocky, stagnant-lid exoplanet can support a global carbon cycle through Galactic history. We apply this framework to a sample of 17 likely rocky exoplanets with measured ages, seven of which we predict are likely to be actively degassing today, despite our pessimistic assumptions. For the remaining planets, including those orbiting TRAPPIST-1, we cannot confidently assume that they currently contain sufficient internal heat to support mantle degassing at a rate sufficient to sustain a global carbon cycle or temperate climate without additional tidal heating or undergoing plate tectonics.
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Dreizler, S., S. V. Jeffers, E. Rodríguez, M. Zechmeister, J. R. Barnes, C. A. Haswell, G. A. L. Coleman et al. « RedDots : a temperate 1.5 Earth-mass planet candidate in a compact multiterrestrial planet system around GJ 1061 ». Monthly Notices of the Royal Astronomical Society 493, no 1 (29 janvier 2020) : 536–50. http://dx.doi.org/10.1093/mnras/staa248.
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ABSTRACT Small low-mass stars are favourable targets for the detection of rocky habitable planets. In particular, planetary systems in the solar neighbourhood are interesting and suitable for precise characterization. The RedDots campaigns seek to discover rocky planets orbiting nearby low-mass stars. The 2018 campaign targeted GJ 1061, which is the 20th nearest star to the Sun. For three consecutive months we obtained nightly, high-precision radial velocity measurements with the HARPS spectrograph. We analysed these data together with archival HARPS data. We report the detection of three planet candidates with periods of 3.204 ± 0.001, 6.689 ± 0.005, and 13.03 ± 0.03 d, which are close to 1:2:4 period commensurability. After several considerations related to the properties of the noise and sampling, we conclude that a fourth signal is most likely explained by stellar rotation, although it may be due to a planet. The proposed three-planet system (and the potential four-planet solution) is long-term dynamically stable. Planet–planet gravitational interactions are below our current detection threshold. The minimum masses of the three planets range from 1.4 ± 0.2 to 1.8 ± 0.3 M⊕. Planet d, with msin i = 1.64 ± 0.24 M⊕, receives a similar amount of energy as Earth receives from the Sun. Consequently it lies within the liquid-water habitable zone of the star and has a similar equilibrium temperature to Earth. GJ 1061 has very similar properties to Proxima Centauri but activity indices point to lower levels of stellar activity.
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Luque, Rafael, et Enric Pallé. « Density, not radius, separates rocky and water-rich small planets orbiting M dwarf stars ». Science 377, no 6611 (9 septembre 2022) : 1211–14. http://dx.doi.org/10.1126/science.abl7164.
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Exoplanets smaller than Neptune are common around red dwarf stars (M dwarfs), with those that transit their host star constituting the bulk of known temperate worlds amenable for atmospheric characterization. We analyze the masses and radii of all known small transiting planets around M dwarfs, identifying three populations: rocky, water-rich, and gas-rich. Our results are inconsistent with the previously known bimodal radius distribution arising from atmospheric loss of a hydrogen/helium envelope. Instead, we propose that a density gap separates rocky from water-rich exoplanets. Formation models that include orbital migration can explain the observations: Rocky planets form within the snow line, whereas water-rich worlds form outside it and later migrate inward.
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Ding, Feng, et Robin D. Wordsworth. « Prospects for Water Vapor Detection in the Atmospheres of Temperate and Arid Rocky Exoplanets around M-dwarf Stars ». Astrophysical Journal Letters 925, no 1 (1 janvier 2022) : L8. http://dx.doi.org/10.3847/2041-8213/ac4a5d.
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Abstract Detection of water vapor in the atmospheres of temperate, rocky exoplanets would be a major milestone on the path toward characterization of exoplanet habitability. Past modeling work has shown that cloud formation may prevent the detection of water vapor on Earth-like planets with surface oceans using the James Webb Space Telescope (JWST). Here we analyze the potential for atmospheric detection of H2O on a different class of targets: arid planets. Using transit spectrum simulations, we show that atmospheric H2O may be easier to detect on arid planets with cold-trapped ice deposits on the surface because such planets will not possess thick H2O cloud decks that limit the transit depth of spectral features. However, additional factors such as band overlap with CO2 and other gases, extinction by mineral dust, overlap of stellar and planetary H2O lines, and the ultimate noise floor obtainable by JWST still pose important challenges. For this reason, a combination of space- and ground-based spectroscopic observations will be essential for reliable detection of H2O on rocky exoplanets in the future.
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Moore, Keavin, et Nicolas B. Cowan. « Keeping M-Earths habitable in the face of atmospheric loss by sequestering water in the mantle ». Monthly Notices of the Royal Astronomical Society 496, no 3 (20 juin 2020) : 3786–95. http://dx.doi.org/10.1093/mnras/staa1796.
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ABSTRACT Water cycling between Earth’s mantle and surface has previously been modelled and extrapolated to rocky exoplanets, but these studies neglected the host star. M-dwarf stars are more common than Sun-like stars and at least as likely to host temperate rocky planets (M-Earths). However, M dwarfs are active throughout their lifetimes; specifically, X-ray and extreme ultraviolet (XUV) radiation during their early evolution can cause rapid atmospheric loss on orbiting planets. The increased bolometric flux reaching M-Earths leads to warmer, moister upper atmospheres, while XUV radiation can photodissociate water molecules and drive hydrogen and oxygen escape to space. Here, we present a coupled model of deep-water cycling and water loss to space on M-Earths to explore whether these planets can remain habitable despite their volatile evolution. We use a cycling parametrization accounting for the dependence of mantle degassing on seafloor pressure, the dependence of regassing on mantle temperature, and the effect of water on mantle viscosity and thermal evolution. We assume the M dwarf’s XUV radiation decreases exponentially with time, and energy-limited water loss with 30 per cent efficiency. We explore the effects of cycling and loss to space on planetary water inventories and water partitioning. Planet surfaces desiccated by loss can be rehydrated, provided there is sufficient water sequestered in the mantle to degas once loss rates diminish at later times. For a given water loss rate, the key parameter is the mantle overturn time-scale at early times: if the mantle overturn time-scale is longer than the loss time-scale, then the planet is likely to keep some of its water.
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Wells, R., K. Poppenhaeger et C. A. Watson. « Validation of a temperate fourth planet in the K2-133 multiplanet system ». Monthly Notices of the Royal Astronomical Society 487, no 2 (16 mai 2019) : 1865–73. http://dx.doi.org/10.1093/mnras/stz1334.
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Abstract We present follow-up observations of the K2-133 multiplanet system. Previously, we announced that K2-133 contained three super-Earths orbiting an M1.5V host star – with tentative evidence of a fourth outer-planet orbiting at the edge of the temperate zone. Here, we report on the validation of the presence of the fourth planet, determining a radius of $1.73_{-0.13}^{+0.14}$ R⊕. The four planets span the radius gap of the exoplanet population, meaning further follow-up would be worthwhile to obtain masses and test theories of the origin of the gap. In particular, the trend of increasing planetary radius with decreasing incident flux in the K2-133 system supports the claim that the gap is caused by photo-evaporation of exoplanet atmospheres. Finally, we note that K2-133 e orbits on the edge of the star's temperate zone, and that our radius measurement allows for the possibility that this is a rocky world. Additional mass measurements are required to confirm or refute this scenario.
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Lobo, Ana H., Aomawa L. Shields, Igor Z. Palubski et Eric Wolf. « Terminator Habitability : The Case for Limited Water Availability on M-dwarf Planets ». Astrophysical Journal 945, no 2 (1 mars 2023) : 161. http://dx.doi.org/10.3847/1538-4357/aca970.
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Abstract Rocky planets orbiting M-dwarf stars are among the most promising and abundant astronomical targets for detecting habitable climates. Planets in the M-dwarf habitable zone are likely synchronously rotating, such that we expect significant day–night temperature differences and potentially limited fractional habitability. Previous studies have focused on scenarios where fractional habitability is confined to the substellar or “eye” region, but in this paper we explore the possibility of planets with terminator habitability, defined by the existence of a habitable band at the transition between a scorching dayside and a glacial nightside. Using a global climate model, we show that for water-limited planets it is possible to have scorching temperatures in the “eye” and freezing temperatures on the nightside, while maintaining a temperate climate in the terminator region, due to reduced atmospheric energy transport. On water-rich planets, however, increasing the stellar flux leads to increased atmospheric energy transport and a reduction in day–night temperature differences, such that the terminator does not remain habitable once the dayside temperatures approach runaway or moist greenhouse limits. We also show that while water-abundant simulations may result in larger fractional habitability, they are vulnerable to water loss through cold trapping on the nightside surface or atmospheric water vapor escape, suggesting that even if planets were formed with abundant water, their climates could become water-limited and subject to terminator habitability.
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Laliotis, Katherine, Jennifer A. Burt, Eric E. Mamajek, Zhexing Li, Volker Perdelwitz, Jinglin Zhao, R. Paul Butler et al. « Doppler Constraints on Planetary Companions to Nearby Sun-like Stars : An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions* ». Astronomical Journal 165, no 4 (27 mars 2023) : 176. http://dx.doi.org/10.3847/1538-3881/acc067.
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Abstract Directly imaging temperate rocky planets orbiting nearby, Sun-like stars with a 6 m class IR/O/UV space telescope, recently dubbed the Habitable Worlds Observatory, is a high-priority goal of the Astro2020 Decadal Survey. To prepare for future direct imaging (DI) surveys, the list of potential targets should be thoroughly vetted to maximize efficiency and scientific yield. We present an analysis of archival radial velocity data for southern stars from the NASA/NSF Extreme Precision Radial Velocity (EPRV) Working Group’s list of high-priority target stars for future DI missions (drawn from the HabEx, LUVOIR, and Starshade Rendezvous studies). For each star, we constrain the region of companion mass and period parameter space we are already sensitive to based on the observational baseline, sampling, and precision of the archival radial velocity (RV) data. Additionally, for some of the targets, we report new estimates of magnetic activity cycle periods, rotation periods, improved orbital parameters for previously known exoplanets, and new candidate planet signals that require further vetting or observations to confirm. Our results show that for many of these stars we are not yet sensitive to even Saturn-mass planets in the habitable zone, let alone smaller planets, highlighting the need for future EPRV vetting efforts before the launch of a DI mission. We present evidence that the candidate temperate super-Earth exoplanet HD 85512b is most likely due to the star’s rotation, and report an RV acceleration for δ Pav that supports the existence of a distant giant planet previously inferred from astrometry.
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Krissansen-Totton, J., et J. J. Fortney. « Predictions for Observable Atmospheres of Trappist-1 Planets from a Fully Coupled Atmosphere–Interior Evolution Model ». Astrophysical Journal 933, no 1 (1 juillet 2022) : 115. http://dx.doi.org/10.3847/1538-4357/ac69cb.
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Abstract The Trappist-1 planets provide a unique opportunity to test the current understanding of rocky planet evolution. The James Webb Space Telescope is expected to characterize the atmospheres of these planets, potentially detecting CO2, CO, H2O, CH4, or abiotic O2 from water photodissociation and subsequent hydrogen escape. Here, we apply a coupled atmosphere–interior evolution model to the Trappist-1 planets to anticipate their modern atmospheres. This model, which has previously been validated for Earth and Venus, connects magma ocean crystallization to temperate geochemical cycling. Mantle convection, magmatic outgassing, atmospheric escape, crustal oxidation, a radiative-convective climate model, and deep volatile cycling are explicitly coupled to anticipate bulk atmospheres and planetary redox evolution over 8 Gyr. By adopting a Monte Carlo approach that samples a broad range of initial conditions and unknown parameters, we make some tentative predictions about current Trappist-1 atmospheres. We find that anoxic atmospheres are probable, but not guaranteed, for the outer planets; oxygen produced via hydrogen loss during the pre-main sequence is typically consumed by crustal sinks. In contrast, oxygen accumulation on the inner planets occurs in around half of all models runs. Complete atmospheric erosion is possible but not assured for the inner planets (occurs in 20%–50% of model runs), whereas the outer planets retain significant surface volatiles in virtually all model simulations. For all planets that retain substantial atmospheres, CO2-dominated or CO2–O2 atmospheres are expected; water vapor is unlikely to be a detectable atmospheric constituent in most cases. There are necessarily many caveats to these predictions, but the ways in which they misalign with upcoming observations will highlight gaps in terrestrial planet knowledge.
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Lingam, Manasvi, et Abraham Loeb. « Characteristics of aquatic biospheres on temperate planets around Sun-like stars and M dwarfs ». Monthly Notices of the Royal Astronomical Society 503, no 3 (4 mars 2021) : 3434–48. http://dx.doi.org/10.1093/mnras/stab611.
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ABSTRACT Aquatic biospheres reliant on oxygenic photosynthesis are expected to play an important role on Earth-like planets endowed with large-scale oceans insofar as carbon fixation (i.e. biosynthesis of organic compounds) is concerned. We investigate the properties of aquatic biospheres comprising Earth-like biota for habitable rocky planets orbiting Sun-like stars and late-type M dwarfs such as TRAPPIST-1. In particular, we estimate how these characteristics evolve with the available flux of photosynthetically active radiation (PAR) and the ambient ocean temperature (TW), the latter of which constitutes a key environmental variable. We show that many salient properties, such as the depth of the photosynthesis zone and the net primary productivity (i.e. the effective rate of carbon fixation), are sensitive to PAR flux and TW and decline substantially when the former is decreased or the latter is increased. We conclude by exploring the implications of our analysis for exoplanets around Sun-like stars and M dwarfs.
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Garcia, Valeria, Cole M. Smith, Daniel R. Chavas et Thaddeus D. Komacek. « Tropical Cyclones on Tidally Locked Rocky Planets : Dependence on Rotation Period ». Astrophysical Journal 965, no 1 (1 avril 2024) : 5. http://dx.doi.org/10.3847/1538-4357/ad2ea5.
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Abstract Tropical cyclones occur over the Earth’s tropical oceans, with characteristic genesis regions and tracks tied to the warm ocean surface that provide energy to sustain these storms. The study of tropical cyclogenesis and evolution on Earth has led to the development of environmental favorability metrics that predict the strength of potential storms from the local background climate state. Simulations of the gamut of transiting terrestrial exoplanets orbiting late-type stars may offer a test of this Earth-based understanding of tropical cyclogenesis. Previous work has demonstrated that tropical cyclones are likely to form on tidally locked terrestrial exoplanets with intermediate rotation periods of ∼8–10 days. In this study, we test these expectations using ExoCAM simulations with both a sufficient horizontal resolution of 0.°47 × 0.°63 required to permit tropical cyclogenesis along with a thermodynamically active slab ocean. We conduct simulations of tidally locked and ocean-covered Earth-sized planets orbiting late-type M dwarf stars with varying rotation periods from 4–16 days in order to cross the predicted maximum in tropical cyclogenesis. We track tropical cyclones that form in each simulation and assess their location of maximum wind, evolution, and maximum wind speeds. We compare the resulting tropical cyclone locations and strengths to predictions based on environmental favorability metrics, finding good agreement between Earth-based metrics and our simulated storms with a local maximum in both tropical cyclone frequency and intensity at a rotation period of 8 days. Our results suggest that environmental favorability metrics used for tropical cyclones on Earth may also be applicable to temperate tidally locked Earth-sized rocky exoplanets with abundant surface liquid water.
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Kipping, David. « Formulation and resolutions of the red sky paradox ». Proceedings of the National Academy of Sciences 118, no 26 (21 juin 2021) : e2026808118. http://dx.doi.org/10.1073/pnas.2026808118.
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Most stars in the Universe are red dwarfs. They outnumber stars like our Sun by a factor of 5 and outlive them by another factor of 20 (population-weighted mean). When combined with recent observations uncovering an abundance of temperate, rocky planets around these diminutive stars, we are faced with an apparent logical contradiction—Why do we not see a red dwarf in our sky? To address this “red sky paradox,” we formulate a Bayesian probability function concerning the odds of finding oneself around an F/G/K-spectral type (Sun-like) star. If the development of intelligent life from prebiotic chemistry is a universally rapid and ensured process, the temporal advantage of red dwarfs dissolves, softening the red sky paradox, but exacerbating the classic Fermi paradox. Otherwise, we find that humanity appears to be a 1-in-100 outlier. While this could be random chance (resolution I), we outline three other nonmutually exclusive resolutions (II to IV) that broadly act as filters to attenuate the suitability of red dwarfs for complex life. Future observations may be able to provide support for some of these. Notably, if surveys reveal a paucity of temperate rocky planets around the smallest (and most numerous) red dwarfs, then this would support resolution II. As another example, if future characterization efforts were to find that red dwarf worlds have limited windows for complex life due to stellar evolution, this would support resolution III. Solving this paradox would reveal guidance for the targeting of future remote life sensing experiments and the limits of life in the cosmos.
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Grimm, Simon L., Brice-Olivier Demory, Michaël Gillon, Caroline Dorn, Eric Agol, Artem Burdanov, Laetitia Delrez et al. « The nature of the TRAPPIST-1 exoplanets ». Astronomy & ; Astrophysics 613 (mai 2018) : A68. http://dx.doi.org/10.1051/0004-6361/201732233.
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Context. The TRAPPIST-1 system hosts seven Earth-sized, temperate exoplanets orbiting an ultra-cool dwarf star. As such, it represents a remarkable setting to study the formation and evolution of terrestrial planets that formed in the same protoplanetary disk. While the sizes of the TRAPPIST-1 planets are all known to better than 5% precision, their densities have significant uncertainties (between 28% and 95%) because of poor constraints on the planet’s masses. Aims. The goal of this paper is to improve our knowledge of the TRAPPIST-1 planetary masses and densities using transit-timing variations (TTVs). The complexity of the TTV inversion problem is known to be particularly acute in multi-planetary systems (convergence issues, degeneracies and size of the parameter space), especially for resonant chain systems such as TRAPPIST-1. Methods. To overcome these challenges, we have used a novel method that employs a genetic algorithm coupled to a full N-body integrator that we applied to a set of 284 individual transit timings. This approach enables us to efficiently explore the parameter space and to derive reliable masses and densities from TTVs for all seven planets. Results. Our new masses result in a five- to eight-fold improvement on the planetary density uncertainties, with precisions ranging from 5% to 12%. These updated values provide new insights into the bulk structure of the TRAPPIST-1 planets. We find that TRAPPIST-1 c and e likely have largely rocky interiors, while planets b, d, f, g, and h require envelopes of volatiles in the form of thick atmospheres, oceans, or ice, in most cases with water mass fractions less than 5%.
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Madhusudhan, Nikku, Subhajit Sarkar, Savvas Constantinou, Måns Holmberg, Anjali A. A. Piette et Julianne I. Moses. « Carbon-bearing Molecules in a Possible Hycean Atmosphere ». Astrophysical Journal Letters 956, no 1 (1 octobre 2023) : L13. http://dx.doi.org/10.3847/2041-8213/acf577.
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Abstract The search for habitable environments and biomarkers in exoplanetary atmospheres is the holy grail of exoplanet science. The detection of atmospheric signatures of habitable Earth-like exoplanets is challenging owing to their small planet–star size contrast and thin atmospheres with high mean molecular weight. Recently, a new class of habitable exoplanets, called Hycean worlds, has been proposed, defined as temperate ocean-covered worlds with H2-rich atmospheres. Their large sizes and extended atmospheres, compared to rocky planets of the same mass, make Hycean worlds significantly more accessible to atmospheric spectroscopy with JWST. Here we report a transmission spectrum of the candidate Hycean world K2-18 b, observed with the JWST NIRISS and NIRSpec instruments in the 0.9–5.2 μm range. The spectrum reveals strong detections of methane (CH4) and carbon dioxide (CO2) at 5σ and 3σ confidence, respectively, with high volume mixing ratios of ∼1% each in a H2-rich atmosphere. The abundant CH4 and CO2, along with the nondetection of ammonia (NH3), are consistent with chemical predictions for an ocean under a temperate H2-rich atmosphere on K2-18 b. The spectrum also suggests potential signs of dimethyl sulfide (DMS), which has been predicted to be an observable biomarker in Hycean worlds, motivating considerations of possible biological activity on the planet. The detection of CH4 resolves the long-standing missing methane problem for temperate exoplanets and the degeneracy in the atmospheric composition of K2-18 b from previous observations. We discuss possible implications of the findings, open questions, and future observations to explore this new regime in the search for life elsewhere.
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Simonetti, Paolo, Giovanni Vladilo, Laura Silva, Michele Maris, Stavro L. Ivanovski, Lorenzo Biasiotti, Matej Malik et Jost von Hardenberg. « EOS : Atmospheric Radiative Transfer in Habitable Worlds with HELIOS ». Astrophysical Journal 925, no 2 (31 janvier 2022) : 105. http://dx.doi.org/10.3847/1538-4357/ac32ca.
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Abstract We present EOS, a procedure for determining the outgoing longwave radiation (OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions expected to be present in the atmospheres of rocky planets with temperate conditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly available atmospheric radiative transfer (RT) codes optimized for fast calculations with GPU processors. These codes were originally developed for the study of giant planets. In this paper we present an adaptation for applications to terrestrial-type, habitable planets, adding specific physical recipes for the gas opacity and vertical structure of the atmosphere. To test the reliability of the procedure, we assessed the impact of changing line opacity profile, continuum opacity model, atmospheric lapse rate, and tropopause position prescriptions on the OLR and the TOA albedo. The results obtained with EOS are in line with those of other RT codes running on traditional CPU processors, while being at least one order of magnitude faster. The adoption of OLR and TOA albedo data generated with EOS in a zonal and seasonal climate model correctly reproduces the fluxes of the present-day Earth measured by the CERES spacecraft. The results of this study disclose the possibility to incorporate fast RT calculations in climate models aimed at characterizing the atmospheres of habitable exoplanets.
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Sestovic, Marko, et Brice-Olivier Demory. « Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2 ». Astronomy & ; Astrophysics 641 (septembre 2020) : A170. http://dx.doi.org/10.1051/0004-6361/202037732.
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Context. With the discovery of a planetary system around the ultracool dwarf TRAPPIST-1, there has been a surge of interest in such stars as potential planet hosts. Planetary systems around ultracool dwarfs represent our best chance of characterising temperate rocky-planet atmospheres with the James Webb Space Telescope. However, TRAPPIST-1 remains the only known system of its kind and the occurrence rate of planets around ultracool dwarfs is still poorly constrained. Aims. We seek to perform a complete transit search on the ultracool dwarfs observed by NASA’s K2 mission, and use the results to constrain the occurrence rate of planets around these stars. Methods. We filter and characterise the sample of ultracool dwarfs observed by K2 by fitting their spectral energy distributions and using parallaxes from Gaia. We build an automatic pipeline to perform photometry, detrend the light curves, and search for transit signals. Using extensive injection-recovery tests of our pipeline, we compute the detection sensitivity of our search, and thus the completeness of our sample. We infer the planetary occurrence rates within a hierarchical Bayesian model (HBM) to treat uncertain planetary parameters. With the occurrence rate parametrised by a step-wise function, we present a convenient way to directly marginalise over the second level of our HBM (the planetary parameters). Our method is applicable generally and can greatly speed up inference with larger catalogues of detected planets. Results. We detect one planet in our sample of 702 ultracool dwarfs: a previously validated mini-Neptune. We thus infer a mini-Neptune (2−4 R⊕) occurrence rate of η = 0.20−0.11+0.16 within orbital periods of 1−20 days. For super-Earths (1−2 R⊕) and ice or gas giants (4−6 R⊕) within 1−20 days, we place 95% credible intervals of η < 1.14 and η < 0.29, respectively. If TRAPPIST-1-like systems were ubiquitous, we would have a ~96% chance of finding at least one.
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Cadieux, Charles, René Doyon, Mykhaylo Plotnykov, Guillaume Hébrard, Farbod Jahandar, Étienne Artigau, Diana Valencia et al. « TOI-1452 b : SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf ». Astronomical Journal 164, no 3 (12 août 2022) : 96. http://dx.doi.org/10.3847/1538-3881/ac7cea.
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Abstract Exploring the properties of exoplanets near or inside the radius valley provides insight on the transition from the rocky super-Earths to the larger, hydrogen-rich atmosphere mini-Neptunes. Here, we report the discovery of TOI-1452b, a transiting super-Earth (R p = 1.67 ± 0.07 R ⊕) in an 11.1 day temperate orbit (T eq = 326 ± 7 K) around the primary member (H = 10.0, T eff = 3185 ± 50 K) of a nearby visual-binary M dwarf. The transits were first detected by the Transiting Exoplanet Survey Satellite, then successfully isolated between the two 3.″2 companions with ground-based photometry from the Observatoire du Mont-Mégantic and MuSCAT3. The planetary nature of TOI-1452b was established through high-precision velocimetry with the near-infrared SPIRou spectropolarimeter as part of the ongoing SPIRou Legacy Survey. The measured planetary mass (4.8 ± 1.3 M ⊕) and inferred bulk density ( 5.6 − 1.6 + 1.8 g cm−3) is suggestive of a rocky core surrounded by a volatile-rich envelope. More quantitatively, the mass and radius of TOI-1452b, combined with the stellar abundance of refractory elements (Fe, Mg, and Si) measured by SPIRou, is consistent with a core-mass fraction of 18% ± 6% and a water-mass fraction of 22 − 13 + 21 %. The water world candidate TOI-1452b is a prime target for future atmospheric characterization with JWST, featuring a transmission spectroscopy metric similar to other well-known temperate small planets such as LHS 1140b and K2-18 b. The system is located near Webb’s northern continuous viewing zone, implying that is can be followed at almost any moment of the year.
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Mollière, P., et I. A. G. Snellen. « Detecting isotopologues in exoplanet atmospheres using ground-based high-dispersion spectroscopy ». Astronomy & ; Astrophysics 622 (février 2019) : A139. http://dx.doi.org/10.1051/0004-6361/201834169.
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Context. The cross-correlation technique is a well-tested method for exoplanet characterization, having lead to the detection of various molecules, to constraints on atmospheric temperature profiles, wind speeds, and planetary spin rates. A new, potentially powerful application of this technique is the measurement of atmospheric isotope ratios. In particular D/H can give unique insights into the formation and evolution of planets, and their atmospheres. Aims. In this paper we aim to study the detectability of molecular isotopologues in the high-dispersion spectra of exoplanet atmospheres, to identify the optimal wavelength ranges to conduct such studies, and to predict the required observational efforts – both with current and future ground-based instrumentation. Methods. High-dispersion (R = 100 000) thermal emission spectra, and in some cases reflection spectra, were simulated by self-consistent modeling of the atmospheric structures and abundances of exoplanets over a wide range of effective temperatures. These were synthetically observed with a telescope equivalent to the VLT and/or ELT, and analyzed using the cross-correlation technique, resulting in signal-to-noise ratio predictions for the 13CO, HDO, and CH3D isotopologues. Results. We find that for the best observable exoplanets, 13CO is well in range of current telescopes. We predict it will be most favorably detectable at 2.4 μm, just longward of the wavelength regions probed by several high-dispersion spectroscopic observations presented in the literature. CH3D can be best targeted at 4.7 μm, and may be detectable using 40 m-class telescopes for planets below 600 K in equilibrium temperature. In this case, the sky background becomes the dominating noise source for self-luminous planets. HDO is best targeted at 3.7 μm, and is less affected by sky background noise. 40 m-class telescopes may lead to its detection for planets with Tequ below 900 K. It could already be in the range of current 8 m-class telescopes in the case of quenched methane abundances. Finally, if Proxima Cen b is water-rich, the HDO isotopologue could be detected with the ELT in ~1 night of observing time in its reflected-light spectrum. Conclusions. Isotopologues will soon be a part of the exoplanet characterisation tools. Measuring D/H in exoplanets, and ratios of other isotopes, could become a prime science case for the first-light instrument METIS on the European ELT, especially for nearby temperate rocky and ice giant planets. This can provide unique insights in their history of icy-body enrichment and atmospheric evaporation processes.
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Cadieux, Charles, Mykhaylo Plotnykov, René Doyon, Diana Valencia, Farbod Jahandar, Lisa Dang, Martin Turbet et al. « New Mass and Radius Constraints on the LHS 1140 Planets : LHS 1140 b Is either a Temperate Mini-Neptune or a Water World ». Astrophysical Journal Letters 960, no 1 (1 janvier 2024) : L3. http://dx.doi.org/10.3847/2041-8213/ad1691.
Texte intégralRésumé :
Abstract The two-planet transiting system LHS 1140 has been extensively observed since its discovery in 2017, notably with Spitzer, HST, TESS, and ESPRESSO, placing strong constraints on the parameters of the M4.5 host star and its small temperate exoplanets, LHS 1140 b and c. Here, we reanalyze the ESPRESSO observations of LHS 1140 with the novel line-by-line framework designed to fully exploit the radial velocity content of a stellar spectrum while being resilient to outlier measurements. The improved radial velocities, combined with updated stellar parameters, consolidate our knowledge of the mass of LHS 1140 b (5.60 ± 0.19 M ⊕) and LHS 1140 c (1.91 ± 0.06 M ⊕) with an unprecedented precision of 3%. Transits from Spitzer, HST, and TESS are jointly analyzed for the first time, allowing us to refine the planetary radii of b (1.730 ± 0.025 R ⊕) and c (1.272 ± 0.026 R ⊕). Stellar abundance measurements of refractory elements (Fe, Mg, and Si) obtained with NIRPS are used to constrain the internal structure of LHS 1140 b. This planet is unlikely to be a rocky super-Earth, as previously reported, but rather a mini-Neptune with a ∼0.1% H/He envelope by mass or a water world with a water-mass fraction between 9% and 19%, depending on the atmospheric composition and relative abundance of Fe and Mg. While the mini-Neptune case would not be habitable, a water-abundant LHS 1140 b potentially has habitable surface conditions according to 3D global climate models, suggesting liquid water at the substellar point for atmospheres with relatively low CO2 concentration, from Earth-like to a few bars.
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Lim, Olivia, Björn Benneke, René Doyon, Ryan J. MacDonald, Caroline Piaulet, Étienne Artigau, Louis-Philippe Coulombe et al. « Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS : Evidence for Strong Stellar Contamination in the Transmission Spectra ». Astrophysical Journal Letters 955, no 1 (1 septembre 2023) : L22. http://dx.doi.org/10.3847/2041-8213/acf7c4.
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Abstract TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique.
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Noack, Lena, et Marine Lasbleis. « Parameterisations of interior properties of rocky planets ». Astronomy & ; Astrophysics 638 (juin 2020) : A129. http://dx.doi.org/10.1051/0004-6361/202037723.
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Context. Observations of Earth-sized exoplanets are mostly limited to information on their masses and radii. Simple mass-radius relationships have been developed for scaled-up versions of Earth or other planetary bodies such as Mercury and Ganymede, as well as for one-material spheres made of pure water(-ice), silicates, or iron. However, they do not allow a thorough investigation of composition influences and thermal state on a planet’s interior structure and properties. Aims. In this work, we investigate the structure of a rocky planet shortly after formation and at later stages of thermal evolution assuming the planet is differentiated into a metal core and a rocky mantle (consisting of Earth-like minerals, but with a variable iron content). Methods. We derived possible initial temperature profiles after the accretion and magma ocean solidification. We then developed parameterisations for the thermodynamic properties inside the core depending on planet mass, composition, and thermal state. Results. We provide the community with robust scaling laws for the interior structure, temperature profiles, and core- and mantle-averaged thermodynamic properties for planets composed of Earth’s main minerals but with variable compositions of iron and silicates. Conclusions. The scaling laws make it possible to investigate variations in thermodynamic properties for different interior thermal states in a multitude of applications such as deriving mass-radius scaling laws or estimating magnetic field evolution and core crystallisation for rocky exoplanets.
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Koll, Daniel D. B. « A Scaling for Atmospheric Heat Redistribution on Tidally Locked Rocky Planets ». Astrophysical Journal 924, no 2 (1 janvier 2022) : 134. http://dx.doi.org/10.3847/1538-4357/ac3b48.
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Abstract Atmospheric heat redistribution shapes the remote appearance of rocky exoplanets, but there is currently no easy way to predict a planet’s heat redistribution from its physical properties. This paper proposes an analytical scaling theory for the heat redistribution on tidally locked rocky exoplanets. The main parameters of the scaling are a planet’s equilibrium temperature, surface pressure, and broadband longwave optical thickness. The scaling compares favorably against idealized general circulation model simulations of TRAPPIST-1b, GJ1132b, and LHS 3844b. For these planets, heat redistribution generally becomes efficient, and a planet’s observable thermal phase curve and secondary eclipse start to deviate significantly from that of a bare rock, once surface pressure exceeds ( 1 ) bar. The scaling additionally points to planetary scenarios for which heat transport can be notably more or less efficient, such as H2 and CO atmospheres or hot lava ocean worlds. The results thus bridge the gap between theory and imminent observations with the James Webb Space Telescope. They can also be used to parameterize the effect of 3D atmospheric dynamics in 1D models, thereby improving the self-consistency of such models.
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Auclair-Desrotour, P., et K. Heng. « Atmospheric stability and collapse on tidally locked rocky planets ». Astronomy & ; Astrophysics 638 (juin 2020) : A77. http://dx.doi.org/10.1051/0004-6361/202037513.
Texte intégralRésumé :
Context. Over large timescales, a terrestrial planet may be driven towards spin-orbit synchronous rotation by tidal forces. In this particular configuration, the planet exhibits permanent dayside and nightside, which may induce strong day-night temperature gradients. The nightside temperature depends on the efficiency of the day-night heat redistribution and determines the stability of the atmosphere against collapse. Aims. To better constrain the atmospheric stability, climate, and surface conditions of rocky planets located in the habitable zone of their host star, it is thus crucial to understand the complex mechanism of heat redistribution. Methods. Building on early works and assuming dry thermodynamics, we developed a hierarchy of analytic models taking into account the coupling between radiative transfer, dayside convection, and large-scale atmospheric circulation in the case of slowly rotating planets. There are two types of these models: a zero-dimensional two-layer approach and a two-column radiative-convective-subsiding-upwelling model. They yield analytical solutions and scaling laws characterising the dependence of the collapse pressure on physical features, which are compared to the results obtained by early works using 3D global climate models (GCMs). Results. The analytical theory captures (i) the dependence of temperatures on atmospheric opacities and scattering in the shortwave and in the longwave, (ii) the behaviour of the collapse pressure observed in GCM simulations at low stellar fluxes that are due to the non-linear dependence of the atmospheric opacity on the longwave optical depth at the planet’s surface, (iii) the increase of stability generated by dayside sensible heating, and (iv) the decrease of stability induced by the increase of the planet size.
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Wang, Luqi, Yibing Zhang, Jian Guo, Qiang Ou, Songlin Liu et Lin Wang. « Study on the Catastrophic Evolution of Tianshan Road Slope under the Freeze-Thaw Cycles ». Geofluids 2021 (4 octobre 2021) : 1–12. http://dx.doi.org/10.1155/2021/6128843.
Texte intégralRésumé :
The maximum temperature difference of Tianshan Road can reach 77.4°C in a year. Under such complex mechanical environment, the mechanical properties of rock mass and structural planes will change significantly as the increase of freeze-thaw cycles (FTC). Consequently, the FTC has become a key factor in the instability and failure of rocky slopes along the Tianshan Road. In this paper, the progressive deformation of rocky slopes and sudden failure process after critical instability were studied through the FTC tests of rock mass and structural planes, discrete element method, and theoretical analysis. The results show that the structural planes and internal microcracks of the rock mass expand under the action of the FTC, causing a gradual decrease in the stability of the slope. The dynamic collapse of the rocky slope has a certain degree of randomness caused by the spatial distribution of structural planes and the interaction between the rock fragments. Due to the limitation of the slipping space and the tilt angle of the trailing edge of the slope, long-distance migration did not occur, and the in situ accumulation of the slope was obvious after failure. The analysis method in this paper can provide an important reference for guiding the catastrophe mechanism analysis and protection of engineering slopes in cold regions.
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Kislyakova, Kristina, et Lena Noack. « Electromagnetic induction heating as a driver of volcanic activity on massive rocky planets ». Astronomy & ; Astrophysics 636 (avril 2020) : L10. http://dx.doi.org/10.1051/0004-6361/202037924.
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Aims. We investigate possible driving mechanisms of volcanic activity on rocky super-Earths with masses exceeding 3–4 M⊕. Due to high gravity and pressures in the mantles of these planets, melting in deep mantle layers can be suppressed, even if the energy release due to tidal heating and radioactive decay is substantial. Here we investigate whether a newly identified heating mechanism, namely induction heating by the star’s magnetic field, can drive volcanic activity on these planets due to its unique heating pattern in the very upper part of the mantle. In this region the pressure is not yet high enough to preclude the melt formation. Methods. Using the super-Earth HD 3167b as an example, we calculate induction heating in the planet’s interiors assuming an electrical conductivity profile typical of a hot rocky planet and a moderate stellar magnetic field typical of an old inactive star. Then we use a mantle convection code (CHIC) to simulate the evolution of volcanic outgassing with time. Results. We show that although in most cases volcanic outgassing on HD 3167b is not very significant in the absence of induction heating, including this heating mechanism changes the picture and leads to a substantial increase in the outgassing from the planet’s mantle. This result shows that induction heating combined with a high surface temperature is capable of driving volcanism on massive super-Earths, which has important observational implications.
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Cockell, Charles S., Claire Cousins, Paul T. Wilkinson, Karen Olsson-Francis et Ben Rozitis. « Are thermophilic microorganisms active in cold environments ? » International Journal of Astrobiology 14, no 3 (10 novembre 2014) : 457–63. http://dx.doi.org/10.1017/s1473550414000433.
Texte intégralRésumé :
AbstractThe mean air temperature of the Icelandic interior is below 10 °C. However, we have previously observed 16S rDNA sequences associated with thermophilic lineages in Icelandic basalts. Measurements of the temperatures of igneous rocks in Iceland showed that solar insolation of these low albedo substrates achieved a peak surface temperature of 44.5 °C. We isolated seven thermophilicGeobacillusspecies from basalt with optimal growth temperatures of ~65 °C. The minimum growth temperature of these organisms was ~36 °C, suggesting that they could be active in the rock environment. Basalt dissolution rates at 40 °C were increased in the presence of one of the isolates compared to abiotic controls, showing its potential to be involved in active biogeochemistry at environmental temperatures. These data raise the possibility of transient active thermophilic growth in macroclimatically cold rocky environments, implying that the biogeographical distribution of active thermophiles might be greater than previously understood. These data show that temperatures measured or predicted over large scales on a planet are not in themselves adequate to assess niches available to extremophiles at micron scales.
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Kashyap Jagadeesh, Madhu, Sagarika Rao Valluri, Vani Kari, Katarzyna Kubska et Łukasz Kaczmarek. « Indexing Exoplanets with Physical Conditions Potentially Suitable for Rock-Dependent Extremophiles ». Life 10, no 2 (26 janvier 2020) : 10. http://dx.doi.org/10.3390/life10020010.
Texte intégralRésumé :
The search for different life forms elsewhere in the universe is a fascinating area of research in astrophysics and astrobiology. Currently, according to the NASA Exoplanet Archive database, 3876 exoplanets have been discovered. The Earth Similarity Index (ESI) is defined as the geometric mean of radius, density, escape velocity, and surface temperature and ranges from 0 (dissimilar to Earth) to 1 (similar to Earth). The ESI was created to index exoplanets on the basis of their similarity to Earth. In this paper, we examined rocky exoplanets whose physical conditions are potentially suitable for the survival of rock-dependent extremophiles, such as the cyanobacteria Chroococcidiopsis and the lichen Acarospora. The Rock Similarity Index (RSI) is first introduced and then applied to 1659 rocky exoplanets. The RSI represents a measure for Earth-like planets on which physical conditions are potentially suitable for rocky extremophiles that can survive in Earth-like extreme habitats (i.e., hot deserts and cold, frozen lands).
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Zhang, Jisheng, et Leslie A. Rogers. « Thermal Evolution and Magnetic History of Rocky Planets ». Astrophysical Journal 938, no 2 (1 octobre 2022) : 131. http://dx.doi.org/10.3847/1538-4357/ac8e65.
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Abstract We present a thermal evolution model coupled with a Henyey solver to study the circumstances under which a rocky planet could potentially host a dynamo in its liquid iron core and/or magma ocean. We calculate the evolution of planet thermal profiles by solving the energy-balance equations for both the mantle and the core. We use a modified mixing length theory to model the convective heat flow in both the magma ocean and solid mantle. In addition, by including the Henyey solver, we self-consistently account for adjustments in the interior structure and heating (cooling) due to planet contraction (expansion). We evaluate whether a dynamo can operate using the critical magnetic Reynolds number. We run simulations to explore how the planet mass (M pl), core mass fraction (CMF), and equilibrium temperature (T eq) affect the evolution and lifetime of possible dynamo sources. We find that the T eq determines the solidification regime of the magma ocean, and only layers with melt fraction greater than a critical value of 0.4 may contribute to the dynamo source region in the magma ocean. We find that the mantle mass, determined by M pl and CMF, controls the thermal isolating effect on the iron core. In addition, we show that the liquid core lasts longer with increasing planet mass. For a core thermal conductivity of 40 Wm−1 K−1, the lifetime of the dynamo in the iron core is limited by the lifetime of the liquid core for 1 M ⊕ planets and by the lack of thermal convection for 3 M ⊕ planets.
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Plotnykov, Mykhaylo, et Diana Valencia. « Chemical fingerprints of formation in rocky super-Earths’ data ». Monthly Notices of the Royal Astronomical Society 499, no 1 (29 août 2020) : 932–47. http://dx.doi.org/10.1093/mnras/staa2615.
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ABSTRACT The composition of rocky exoplanets in the context of stars’ composition provides important constraints to formation theories. In this study, we select a sample of exoplanets with mass and radius measurements with an uncertainty $\lt 25{{\ \rm per\ cent}}$ and obtain their interior structure. We calculate compositional markers, ratios of iron to magnesium and silicon, as well as core mass fractions (CMFs) that fit the planetary parameters, and compare them to the stars. We find four key results that successful planet formation theories need to predict: (1) In a population sense, the composition of rocky planets spans a wider range than stars. The stars’ Fe/Si distribution is close to a Gaussian distribution $1.63^{+0.91}_{-0.85}$, while the planets’ distribution peaks at lower values and has a longer tail, $1.15^{+1.43}_{-0.76}$. It is easier to see the discrepancy in CMF space, where primordial stellar composition is $0.32^{+0.14}_{-0.12}$, while rocky planets follow a broader distribution $0.24^{+0.33}_{-0.18}$. (2) We introduce uncompressed density ($\overline{\rho _0}$ at reference pressure/temperature) as a metric to compare compositions. With this, we find what seems to be the maximum iron enrichment that rocky planets attain during formation ($\overline{\rho _0}\sim 6$ and CMF ∼0.8). (3) Highly irradiated planets exhibit a large range of compositions. If these planets are the result of atmospheric evaporation, iron enrichment and perhaps depletion must happen before gas dispersal. And, (4) We identify a group of highly irradiated planets that, if rocky, would be twofold depleted in Fe/Si with respect to the stars. Without a reliable theory for forming iron-depleted planets, these are interesting targets for follow-up.
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Boukaré, Charles-Édouard, Nicolas B. Cowan et James Badro. « Deep Two-phase, Hemispherical Magma Oceans on Lava Planets ». Astrophysical Journal 936, no 2 (1 septembre 2022) : 148. http://dx.doi.org/10.3847/1538-4357/ac8792.
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Abstract Astronomers have discovered a handful of exoplanets with rocky bulk compositions but orbiting that orbit so close to their host star that the surface of the planet must be at least partially molten. It is expected that the dayside of such “lava planets” harbors a rock-vapor atmosphere that flows quickly toward the airless nightside—this partial atmosphere is critical to the interpretation of lava planet observations, but transports negligible heat toward the nightside. As a result, the surface temperature of the magma ocean may range from 3000 K near the substellar point down to 1500 K near the day–night terminator. We use simple models incorporating the thermodynamics and geochemistry of partial melt to predict the physical and chemical properties of the magma ocean as a function of the distance from the substellar point. Our principal findings are that: (1) the dayside magma ocean is much deeper than previously thought, probably extending down to the core–mantle boundary below the substellar point of an Earth-sized planet; (2) much of the dayside is only partially molten, leading to gradients in the surface chemistry of the magma ocean; and (3) the temperature at the base of the silicate mantle is as important as the surface temperature. In the most extreme cases, lava planet interiors could be cold enough such that thermal stratification below the substellar point is gravitationally stable. These findings have important implications for the dynamics of the magma ocean, as well as the composition and dynamics of the atmosphere.
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Kellermann, C., A. Becker et R. Redmer. « Interior structure models and fluid Love numbers of exoplanets in the super-Earth regime ». Astronomy & ; Astrophysics 615 (juillet 2018) : A39. http://dx.doi.org/10.1051/0004-6361/201731775.
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Space missions such as CoRoT and Kepler have made the transit method the most successful technique in observing extrasolar planets. However, although the mean density of a planet can be derived from its measured mass and radius, no details about its interior structure, such as the density profile, can be inferred so far. If determined precisely enough, the shape of the transiting light curve might, in principle, reveal the shape of the planet, and in particular, its deviation from spherical symmetry. These deformations are caused, for instance, by the tidal interactions of the planet with the host star and by other planets that might orbit in the planetary system. The deformations depend on the interior structure of the planet and its composition and can be parameterized as Love numbers kn. This means that the diversity of possible interior models for extrasolar planets might be confined by measuring this quantity. We present results of a wide-ranging parameter study in planet mass, surface temperature, and layer mass fractions on such models for super-Earths and their corresponding Love numbers. Based on these data, we find that k2 is most useful in assessing the ratio of rocky material to iron and in ruling out certain compositional configurations for measured mass and radius values, such as a prominent core consisting of rocky material. Furthermore, we apply the procedure to exoplanets K2-3b and c and predict that K2-3c probably has a thick outer water layer.
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Beldade, Ricardo, Rita Borges et Emanuel J. Gonçalves. « Depth distribution of nearshore temperate fish larval assemblages near rocky substrates ». Journal of Plankton Research 28, no 11 (1 novembre 2006) : 1003–13. http://dx.doi.org/10.1093/plankt/fbl035.
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Protasov, S. I., E. A. Seregin, V. A. Portola et A. A. Bobrovnikova. « Investigation of the Centers of Endogenous Fires at the Rock Dumps of the Coal Enterprises ». Occupational Safety in Industry, no 8 (août 2021) : 65–70. http://dx.doi.org/10.24000/0409-2961-2021-8-65-70.
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The formed rock dumps of sections, mines and washing plants are composed of carbonaceous rocks and are capable of spontaneous combustion when the required amount of air is supplied. The conducted studies evaluated the efficiency of detecting a center of spontaneous combustion at the rock dumps of sections by measuring the temperature of rocks in the wells with a depth of 2.5 m, drilled at the distance of 20 m from each other, according to the current normative documents. For the landfill, a dump site with a long-existing center of spontaneous combustion was selected. The experiment showed the impossibility of drilling wells on the slopes of the dumps, as well as the need for casing the wells with pipes along the entire length. The temperature of rocks in the wells at a depth of 2.5 m varied from 69 to 773 °C. It was found that in the heated zone there are sharp temperature drops in the rocks, which cannot be detected with an interval between the measurement points equal to 20 m. With such a distance between the control wells, the places with a diameter of 1–10 m may remain undetected at the initial stage of spontaneous combustion. Measurements showed that in all the wells the rock temperature increases with depth. At the same time, the recommended well depth of 2.5 m does not allow determining the size of the heated zone deep into the rock dump. The upper layer of rocks above the center of spontaneous combustion exceeds the ambient temperature, so remote temperature measuring devices can be used to detect endogenous fires in the rock dumps. The use of thermal imagers installed on the unmanned aerial vehicles will significantly reduce the cost of detecting spontaneous combustion centers on the rock dumps and increase the efficiency of detecting fire centers not only on the dump sites, but on the slopes of the dump side and in other hard-to-reach places. Moreover, with a decrease in the atmospheric air temperature, the efficiency of remote thermal photography does not decrease. To clarify the parameters of the center of endogenous fires, it is advisable to use the temperature measurement of rocks with a contact thermometer at a depth of 0.5 m.
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Soto, M. G., G. Anglada-Escudé, S. Dreizler, K. Molaverdikhani, J. Kemmer, C. Rodríguez-López, J. Lillo-Box et al. « Mass and density of the transiting hot and rocky super-Earth LHS 1478 b (TOI-1640 b) ». Astronomy & ; Astrophysics 649 (mai 2021) : A144. http://dx.doi.org/10.1051/0004-6361/202140618.
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One of the main objectives of the Transiting Exoplanet Survey Satellite (TESS) mission is the discovery of small rocky planets around relatively bright nearby stars. Here, we report the discovery and characterization of the transiting super-Earth planet orbiting LHS 1478 (TOI-1640). The star is an inactive red dwarf (J ~ 9.6 mag and spectral type m3 V) with mass and radius estimates of 0.20 ± 0.01M⊙ and 0.25 ± 0.01R⊙, respectively, and an effective temperature of 3381 ± 54 K. It was observed by TESS in four sectors. These data revealed a transit-like feature with a period of 1.949 days. We combined the TESS data with three ground-based transit measurements, 57 radial velocity (RV) measurements from CARMENES, and 13 RV measurements from IRD, determining that the signal is produced by a planet with a mass of 2.33−0.20+0.20 M⊕ and a radius of 1.24−0.05+0.05 R⊕. The resulting bulk density of this planet is 6.67 g cm−3, which is consistent with a rocky planet with an Fe- and MgSiO3-dominated composition. Although the planet would be too hot to sustain liquid water on its surface (its equilibrium temperature is about ~595 K, suggesting aVenus-like atmosphere), spectroscopic metrics based on the capabilities of the forthcoming James Webb Space Telescope and the fact that the host star is rather inactive indicate that this is one of the most favorable known rocky exoplanets for atmospheric characterization.
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Tackley, Paul J., Michael M. Ammann, John P. Brodholt, David P. Dobson et Diana Valencia. « Habitable Planets : Interior Dynamics and Long-Term Evolution ». Proceedings of the International Astronomical Union 8, S293 (août 2012) : 339–49. http://dx.doi.org/10.1017/s1743921313013136.
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AbstractHere, the state of our knowledge regarding the interior dynamics and evolution of habitable terrestrial planets including Earth and super-Earths is reviewed, and illustrated using state-of-the-art numerical models. Convection of the rocky mantle is the key process that drives the evolution of the interior: it causes plate tectonics, controls heat loss from the metallic core (which generates the magnetic field) and drives long-term volatile cycling between the atmosphere/ocean and interior. Geoscientists have been studying the dynamics and evolution of Earth's interior since the discovery of plate tectonics in the late 1960s and on many topics our understanding is very good, yet many first-order questions remain. It is commonly thought that plate tectonics is necessary for planetary habitability because of its role in long-term volatile cycles that regulate the surface environment. Plate tectonics is the surface manifestation of convection in the 2900-km deep rocky mantle, yet exactly how plate tectonics arises is still quite uncertain; other terrestrial planets like Venus and Mars instead have a stagnant lithosphere- essentially a single plate covering the entire planet. Nevertheless, simple scalings as well as more complex models indicate that plate tectonics should be easier on larger planets (super-Earths), other things being equal. The dynamics of terrestrial planets, both their surface tectonics and deep mantle dynamics, change over billions of years as a planet cools. Partial melting is a key process influencing solid planet evolution. Due to the very high pressure inside super-Earths' mantles the viscosity would normally be expected to be very high, as is also indicated by our density function theory (DFT) calculations. Feedback between internal heating, temperature and viscosity leads to a superadiabatic temperature profile and self-regulation of the mantle viscosity such that sluggish convection still occurs.
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Guimond, Claire Marie, John F. Rudge et Oliver Shorttle. « Blue Marble, Stagnant Lid : Could Dynamic Topography Avert a Waterworld ? » Planetary Science Journal 3, no 3 (1 mars 2022) : 66. http://dx.doi.org/10.3847/psj/ac562e.
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Abstract Topography on a wet rocky exoplanet could raise land above its sea level. Although land elevation is the product of many complex processes, the large-scale topographic features on any geodynamically active planet are the expression of the convecting mantle beneath the surface. This so-called “dynamic topography” exists regardless of a planet’s tectonic regime or volcanism; its amplitude, with a few assumptions, can be estimated via numerical simulations of convection as a function of the mantle Rayleigh number. We develop new scaling relationships for dynamic topography on stagnant lid planets using 2D convection models with temperature-dependent viscosity. These scalings are applied to 1D thermal history models to explore how dynamic topography varies with exoplanetary observables over a wide parameter space. Dynamic topography amplitudes are converted to an ocean basin capacity, the minimum water volume required to flood the entire surface. Basin capacity increases less steeply with planet mass than does the amount of water itself, assuming a water inventory that is a constant planetary mass fraction. We find that dynamically supported topography alone could be sufficient to maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 10−4 times their mass, in the most favorable thermal states. By considering only dynamic topography, which has ∼1 km amplitudes on Earth, these results represent a lower limit to the true ocean basin capacity. Our work indicates that deterministic geophysical modeling could inform the variability of land propensity on low-mass planets.
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Gao, Tianze, Xiujian Ding, Xianzhang Yang, Changchao Chen, Zhenping Xu, Keyu Liu, Xueqi Zhang et Weizheng Cao. « Geochemical Characteristics and Depositional Environment of Coal-Measure Hydrocarbon Source Rocks in the Northern Tectonic Belt, Kuqa Depression ». Applied Sciences 12, no 19 (21 septembre 2022) : 9464. http://dx.doi.org/10.3390/app12199464.
Texte intégralRésumé :
A total of 21 samples were selected from a total of Jurassic coal-measure source rocks in the northern structural belt of the Kuqa Depression, in the Tarim Basin. By using a carbon-sulfur content analyzer, Rock Eval 7 rock pyrology instrument and gas chromatography–mass spectrometry (GC-MS), the abundance, type, depositional environment, and source of organic matter are confirmed. The factors that control the development of coal-measure hydrocarbon source rocks are analyzed. The pyrolysis parameters of rocks, such as total organic carbon (TOC), hydrocarbon generating potential (S1 + S2), hydrogen index (HI) and the highest pyrolysis peak temperature (Tmax), show that good to excellent coal-measure source rocks constitute the majority, and the types of organic matter are predominantly type III and occasionally type II. Low S/C ratio, high Pr/Ph value, and high C29 regular sterane levels suggest that the environment in which the coal-measure source rocks were deposited was oxidative, and the majority of the organic matter comes from higher terrestrial plants. In addition, the cross plot of isoprenoids with n-alkanes and the triangle diagrams of regular sterane also show that the primary source of organic matters in coal-measure source rocks is terrestrial higher plants. Because the shallow and turbulent water body is not easily stratified, the gammacerane content is low, which reflects the characteristics of low salinity. Combined with the cross plots of isoprenoids, it might be demonstrated that the freshwater environment is where the coal-measure source rocks were deposited. Comprehensive analysis shows that the oxidational and freshwater depositional environment is favorable to coal-measure source rock development.
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Brinkman, Casey L., Lauren M. Weiss, Fei Dai, Daniel Huber, Edwin S. Kite, Diana Valencia, Jacob L. Bean et al. « TOI-561 b : A Low-density Ultra-short-period “Rocky” Planet around a Metal-poor Star ». Astronomical Journal 165, no 3 (7 février 2023) : 88. http://dx.doi.org/10.3847/1538-3881/acad83.
Texte intégralRésumé :
Abstract TOI-561 is a galactic thick-disk star hosting an ultra-short-period (0.45-day-orbit) planet with a radius of 1.37 R ⊕, making it one of the most metal-poor ([Fe/H] = −0.41) and oldest (≈10 Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity (RV) measurements from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of M b = 2.24 ± 0.20 M ⊕. We also used two new sectors of TESS photometry to improve the radius determination, finding R b = 1.37 ± 0.04 R ⊕ and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (ρ b = 4.8 ± 0.5 g cm−3). This density is consistent with an iron-poor rocky composition reflective of the host star’s iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (∼2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters and that further measurements are needed to determine whether TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a nonprimordial envelope on a planet with a radius smaller than 1.5 R ⊕.
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Ih, Jegug, Eliza M. R. Kempton, Emily A. Whittaker et Madeline Lessard. « Constraining the Thickness of TRAPPIST-1 b’s Atmosphere from Its JWST Secondary Eclipse Observation at 15 μm ». Astrophysical Journal Letters 952, no 1 (1 juillet 2023) : L4. http://dx.doi.org/10.3847/2041-8213/ace03b.
Texte intégralRésumé :
Abstract Recently, the first JWST measurement of thermal emission from a rocky exoplanet was reported. The inferred dayside brightness temperature of TRAPPIST-1 b at 15 μm is consistent with the planet having no atmosphere and therefore no mechanism by which to circulate heat to its nightside. In this Letter, we compare TRAPPIST-1 b's measured secondary eclipse depth to predictions from a suite of self-consistent radiative-convective equilibrium models in order to quantify the maximum atmospheric thickness consistent with the observation. We find that plausible atmospheres (i.e., those that contain at least 100 ppm CO2) with surface pressures greater than 0.3 bar are ruled out at 3σ, regardless of the choice of background atmosphere, and a Mars-like thin atmosphere with surface pressure 6.5 mbar composed entirely of CO2 is also ruled out at 3σ. Thicker atmospheres of up to 10 bar (100 bar) are consistent with the data at 1σ (3σ) only if the atmosphere lacks any strong absorbers across the mid-IR wavelength range—a scenario that we deem unlikely. We additionally model the emission spectra for bare-rock planets of various compositions. We find that a basaltic, metal-rich, and Fe-oxidized surface best matches the measured eclipse depth to within 1σ, and the best-fit gray albedo is 0.02 ± 0.11. We conclude that planned secondary eclipse observations at 12.8 μm will serve to validate TRAPPIST-1 b's high observed brightness temperature, but are unlikely to further distinguish among the consistent atmospheric and bare-rock scenarios.
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Mack, C. E., K. G. Strassmeier, I. Ilyin, S. C. Schuler, F. Spada et S. A. Barnes. « PEPSI deep spectra ». Astronomy & ; Astrophysics 612 (avril 2018) : A46. http://dx.doi.org/10.1051/0004-6361/201731634.
Texte intégralRésumé :
Context. With the Large Binocular Telescope (LBT), we obtained a spectrum with PEPSI, its new optical high-resolution échelle spectrograph. The spectrum has very high resolution and a high signal-to-noise (S/N) and is of the K0V host Kepler−444, which is known to host five sub-Earth-sized rocky planets. The spectrum has a resolution of R ≈ 250 000, a continuous wavelength coverage from 4230 Å to 9120 Å, and an S/N between 150–550:1 (blue to red). Aim. We performed a detailed chemical analysis to determine the photospheric abundances of 18 chemical elements. These were used to place constraints on the bulk composition of the five rocky planets. Methods. Our spectral analysis employs the equivalent-width method for most of our spectral lines, but we used spectral synthesis to fit a small number of lines that required special care. In both cases, we derived our abundances using the MOOG spectral analysis package and Kurucz model atmospheres. Results. We find no correlation between elemental abundance and condensation temperature among the refractory elements (TC > 950 K). In addition, using our spectroscopic stellar parameters and isochrone fitting, we find an age of 10 ± 1.5 Gyr, which is consistent with the asteroseismic age of 11 ± 1 Gyr. Finally, from the photospheric abundances of Mg, Si, and Fe, we estimate that the typical Fe-core mass fraction for the rocky planets in the Kepler−444 system is approximately 24%. Conclusions. If our estimate of the Fe-core mass fraction is confirmed by more detailed modeling of the disk chemistry and simulations of planet formation and evolution in the Kepler−444 system, then this would suggest that rocky planets in more metal-poor and α-enhanced systems may tend to be less dense than their counterparts of comparable size in more metal-rich systems.
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Sergeev, Denis E., Thomas J. Fauchez, Martin Turbet, Ian A. Boutle, Kostas Tsigaridis, Michael J. Way, Eric T. Wolf et al. « The TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). II. Moist Cases—The Two Waterworlds ». Planetary Science Journal 3, no 9 (1 septembre 2022) : 212. http://dx.doi.org/10.3847/psj/ac6cf2.
Texte intégralRésumé :
Abstract To identify promising exoplanets for atmospheric characterization and to make the best use of observational data, a thorough understanding of their atmospheres is needed. Three-dimensional general circulation models (GCMs) are one of the most comprehensive tools available for this task and will be used to interpret observations of temperate rocky exoplanets. Due to parameterization choices made in GCMs, they can produce different results, even for the same planet. Employing four widely used exoplanetary GCMs—ExoCAM, LMD-G, ROCKE-3D, and the UM—we continue the TRAPPIST-1 Habitable Atmosphere Intercomparison by modeling aquaplanet climates of TRAPPIST-1e with a moist atmosphere dominated by either nitrogen or carbon dioxide. Although the GCMs disagree on the details of the simulated regimes, they all predict a temperate climate with neither of the two cases pushed out of the habitable state. Nevertheless, the intermodel spread in the global mean surface temperature is nonnegligible: 14 K and 24 K in the nitrogen- and carbon dioxide-dominated case, respectively. We find substantial intermodel differences in moist variables, with the smallest amount of clouds in LMD-Generic and the largest in ROCKE-3D. ExoCAM predicts the warmest climate for both cases and thus has the highest water vapor content and the largest amount and variability of cloud condensate. The UM tends to produce colder conditions, especially in the nitrogen-dominated case due to a strong negative cloud radiative effect on the day side of TRAPPIST-1e. Our study highlights various biases of GCMs and emphasizes the importance of not relying solely on one model to understand exoplanet climates.
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Colose, Christopher M., Jacob Haqq-Misra, Eric T. Wolf, Anthony D. Del Genio, Rory Barnes, Michael J. Way et Reto Ruedy. « Effects of Spin–Orbit Resonances and Tidal Heating on the Inner Edge of the Habitable Zone ». Astrophysical Journal 921, no 1 (27 octobre 2021) : 25. http://dx.doi.org/10.3847/1538-4357/ac135c.
Texte intégralRésumé :
Abstract Much attention has been given to the climate dynamics and habitable boundaries of synchronously rotating planets around low mass stars. However, other rotational states are possible, including spin–orbit resonant configurations, particularly when higher eccentricity orbits can be maintained in a system. Additionally, the oscillating strain as a planet moves from periastron to apoastron results in friction and tidal heating, which can be an important energy source. Here, we simulate the climate of ocean-covered planets near the inner edge of the habitable zone around M to solar stars with the NASA GISS ROCKE-3D general circulation model, and leverage the planetary evolution software package, VPLanet, to calculate tidal heating rates for Earth-sized planets orbiting 2600 and 3000 K stars. This study is the first to use a 3D general circulation model that implements tidal heating to investigate habitability for multiple resonant states. We find that for reference experiments without tidal heating, the resonant state has little impact on the radial position of the inner edge because for a given stellar flux, higher-order states tend to be warmer than synchronous rotators, but for a given temperature, have drier upper atmospheres. However, when strong tidal heating is present, the rotational component implies a strong dependence of habitable conditions on the system evolution and rotational state. Since tidal and stellar heating both decrease rapidly with orbital distance, this results in a compact orbital width separating temperate and uninhabitable climates. We summarize these results and also compare ROCKE-3D to previously published simulations of the inner edge.
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Kasting, James F. « The Goldilocks Planet ? How Silicate Weathering Maintains Earth “Just Right” ». Elements 15, no 4 (1 août 2019) : 235–40. http://dx.doi.org/10.2138/gselements.15.4.235.
Texte intégralRésumé :
Earth's climate is buffered over long timescales by a negative feedback between atmospheric CO2 level and surface temperature. The rate of silicate weathering slows as the climate cools, causing CO2 to increase and warming the surface through the greenhouse effect. This buffering system has kept liquid water stable at Earth's surface, except perhaps during certain ‘Snowball Earth’ episodes at the beginning and end of the Proterozoic. A similar stabilizing feedback is predicted to occur on rocky planets orbiting other stars if they share analogous properties with Earth, most importantly an adequate (but not overly large) abundance of water and a mechanism for recycling carbonate rocks into CO2. Periodic oscillations between globally glaciated and ice-free climates may occur on planets with weak stellar insolation and/or slow volcanic outgassing rates. Most silicate weathering is thought to occur on the continents today, but seafloor weathering (and reverse weathering) may have been equally important earlier in Earth's history.
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Essack, Zahra, Avi Shporer, Jennifer A. Burt, Sara Seager, Saverio Cambioni, Zifan Lin, Karen A. Collins et al. « TOI-1075 b : A Dense, Massive, Ultra-short-period Hot Super-Earth Straddling the Radius Gap ». Astronomical Journal 165, no 2 (10 janvier 2023) : 47. http://dx.doi.org/10.3847/1538-3881/ac9c5b.
Texte intégralRésumé :
Abstract Populating the exoplanet mass–radius diagram in order to identify the underlying relationship that governs planet composition is driving an interdisciplinary effort within the exoplanet community. The discovery of hot super-Earths—a high-temperature, short-period subset of the super-Earth planet population—has presented many unresolved questions concerning the formation, evolution, and composition of rocky planets. We report the discovery of a transiting, ultra-short-period hot super-Earth orbiting TOI-1075 (TIC351601843), a nearby (d = 61.4 pc) late-K/early-M-dwarf star, using data from the Transiting Exoplanet Survey Satellite. The newly discovered planet has a radius of 1.791 − 0.081 + 0.116 R ⊕ and an orbital period of 0.605 day (14.5 hr). We precisely measure the planet mass to be 9.95 − 1.30 + 1.36 M ⊕ using radial velocity measurements obtained with the Planet Finder Spectrograph mounted on the Magellan II telescope. Our radial velocity data also show a long-term trend, suggesting an additional planet in the system. While TOI-1075 b is expected to have a substantial H/He atmosphere given its size relative to the radius gap, its high density ( 9.32 − 1.85 + 2.05 g cm−3) is likely inconsistent with this possibility. We explore TOI-1075 b’s location relative to the M-dwarf radius valley, evaluate the planet’s prospects for atmospheric characterization, and discuss potential planet formation mechanisms. Studying the TOI-1075 system in the broader context of ultra-short-period planetary systems is necessary for testing planet formation and evolution theories and density-enhancing mechanisms and for future atmospheric and surface characterization studies via emission spectroscopy with the JWST.
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Herbort, O., P. Woitke, Ch Helling et A. L. Zerkle. « The atmospheres of rocky exoplanets ». Astronomy & ; Astrophysics 658 (février 2022) : A180. http://dx.doi.org/10.1051/0004-6361/202141636.
Texte intégralRésumé :
Clouds are an integral part of planetary atmospheres, with most planets hosting clouds. Understanding not only the formation, but also the composition of clouds, is crucial to understand future observations. As observations of the planet’s surface will remain very difficult, it is essential to link the observable high atmosphere gas and cloud composition to the surface conditions. We present a fast and simple chemical equilibrium model for the troposphere of rocky exoplanets, which is in chemical and phase equilibrium with the crust. The hydrostatic equilibrium atmosphere is built from bottom to top. In each atmospheric layer, chemical equilibrium is solved and all thermally stable condensates are removed, depleting the atmosphere above in the effected elements. These removed condensates build an upper limit for cloud formation and can be separated into high and low temperature condensates. The most important cloud condensates for 1000 K ≳ Tgas ≳ 400 K are KCl[s], NaCl[s], FeS[s], FeS2[s], FeO[s], Fe2O3[s], and Fe3O4[s]. For Tgas ≲ 400 K H2O[l,s], C[s], NH3[s], NH4Cl[s], and NH4SH[s] are thermally stable, while for even lower temperatures of Tgas ≲ 150 K CO2[s], CH4[s], NH3[s], and H2S[s] become stable. The inclusion of clouds with trace abundances results in the thermal stability of a total of 72 condensates for atmospheres with different surface conditions (300 K ≤ Tsurf ≤ 1000 K and psurf = 1 bar, 100 bar). The different cloud condensates are not independent of each other, but follow sequences of condensation, which are robust against changes in crust composition, surface pressure, and surface temperature. Independent of the existence of water as a crust condensate, H2O[l,s] is a thermally stable cloud condensate for all investigated elemental abundances. However, the water cloud base depends on the hydration level of the crust. Therefore, the detection of water condensates alone does not necessarily imply stable water on the surface, even if the temperature could allow for water condensation.
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Malik, Matej, Eliza M. R. Kempton, Daniel D. B. Koll, Megan Mansfield, Jacob L. Bean et Edwin Kite. « Analyzing Atmospheric Temperature Profiles and Spectra of M Dwarf Rocky Planets ». Astrophysical Journal 886, no 2 (2 décembre 2019) : 142. http://dx.doi.org/10.3847/1538-4357/ab4a05.
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Roussel, E., R. Crec'hriou, P. Lenfant, J. Mader et S. Planes. « Relative influences of space, time and environment on coastal ichthyoplankton assemblages along a temperate rocky shore ». Journal of Plankton Research 32, no 10 (28 mai 2010) : 1443–57. http://dx.doi.org/10.1093/plankt/fbq056.
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Mercier, Samson J., Lisa Dang, Alexander Gass, Nicolas B. Cowan et Taylor J. Bell. « Revisiting the Iconic Spitzer Phase Curve of 55 Cancri e : Hotter Dayside, Cooler Nightside, and Smaller Phase Offset ». Astronomical Journal 164, no 5 (19 octobre 2022) : 204. http://dx.doi.org/10.3847/1538-3881/ac8f22.
Texte intégralRésumé :
Abstract Thermal phase curves of short-period exoplanets provide the best constraints on the atmospheric dynamics and heat transport in their atmospheres. The published Spitzer Space Telescope phase curve of 55 Cancri e, an ultra-short-period super-Earth, exhibits a large phase offset suggesting significant eastward heat recirculation, unexpected on such a hot planet. We present our rereduction and analysis of these iconic observations using the open source and modular Spitzer Phase Curve Analysis pipeline. In particular, we attempt to reproduce the published analysis using the same instrument detrending scheme as the original authors. We retrieve the dayside temperature ( T day = 3771 − 520 + 669 K), nightside temperature ( T night < 1649 K at 2σ), and longitudinal offset of the planet's hot spot, and quantify how they depend on the reduction and detrending. Our reanalysis suggests that 55 Cancri e has a negligible hot spot offset of − 12 − 18 + 21 degrees east. The small phase offset and cool nightside are consistent with the poor heat transport expected on ultra-short-period planets. The high dayside 4.5 μm brightness temperature is qualitatively consistent with SiO emission from an inverted rock vapor atmosphere.
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Zeng, Li, Stein B. Jacobsen, Eugenia Hyung, Amit Levi, Chantanelle Nava, James Kirk, Caroline Piaulet et al. « New Perspectives on the Exoplanet Radius Gap from a Mathematica Tool and Visualized Water Equation of State ». Astrophysical Journal 923, no 2 (1 décembre 2021) : 247. http://dx.doi.org/10.3847/1538-4357/ac3137.
Texte intégralRésumé :
Abstract Recent astronomical observations obtained with the Kepler and TESS missions and their related ground-based follow-ups revealed an abundance of exoplanets with a size intermediate between Earth and Neptune (1 R ⊕ ≤ R ≤ 4 R ⊕). A low occurrence rate of planets has been identified at around twice the size of Earth (2 × R ⊕), known as the exoplanet radius gap or radius valley. We explore the geometry of this gap in the mass–radius diagram, with the help of a Mathematica plotting tool developed with the capability of manipulating exoplanet data in multidimensional parameter space, and with the help of visualized water equations of state in the temperature–density (T–ρ) graph and the entropy–pressure (s–P) graph. We show that the radius valley can be explained by a compositional difference between smaller, predominantly rocky planets (<2 × R ⊕) and larger planets (>2 × R ⊕) that exhibit greater compositional diversity including cosmic ices (water, ammonia, methane, etc.) and gaseous envelopes. In particular, among the larger planets (>2 × R ⊕), when viewed from the perspective of planet equilibrium temperature (T eq), the hot ones (T eq ≳ 900 K) are consistent with ice-dominated composition without significant gaseous envelopes, while the cold ones (T eq ≲ 900 K) have more diverse compositions, including various amounts of gaseous envelopes.
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Rogers, Leslie A., et Sara Seager. « GJ 1214b and the prospects for liquid water on super Earths ». Proceedings of the International Astronomical Union 6, S276 (octobre 2010) : 189–92. http://dx.doi.org/10.1017/s1743921311020163.
Texte intégralRésumé :
AbstractGJ 1214b is one of the first discovered transiting planets having mass (6.55 M⊕) and radius (2.678 R⊕) smaller than Neptune. To account for its low average density (1870 kg m−3), GJ 1214b must have a significant gas component. We use interior structure models to constrain GJ 1214b's gas envelope mass, and to explore the conditions needed to achieve within the planet pressures and temperatures conducive to liquid water. We consider three possible origins for the gas layer: direct accretion of gas from the protoplanetary nebula, sublimation of ices, and outgassing from rocky material. Despite having an equilibrium temperature below 647 K (the critical temperature of water) GJ 1214b does not have liquid water under most conditions we consider. Even if the outer envelope is predominantly sublimated water ice, in our model a low intrinsic planet luminosity (less than 2 TW) is needed for the water envelope to pass through the liquid phase; at higher interior luminosities the outer envelope transitions from a vapor to a super-fluid then to a plasma at successively greater depths.