Possible climates on terrestrial exoplanets

What kind of environment may exist on terrestrial planets around other stars? In spite of the lack of direct observations, it may not be premature to speculate on exoplanetary climates, for instance to optimize future telescopic observations, or to assess the probability of habitable worlds. To first order, climate primarily depends on 1) The atmospheric composition and the volatile inventory; 2) The incident stellar flux; 3) The tidal evolution of the planetary spin, which can notably lock a planet with a permanent night side. The atmospheric composition and mass depends on complex processes which are difficult to model: origins of volatile, atmospheric escape, geochemistry, photochemistry. We discuss physical constraints which can help us to speculate on the possible type of atmosphere, depending on the planet size, its final distance for its star and the star type. Assuming that the atmosphere is known, the possible climates can be explored using Global Climate Models analogous to the ones developed to simulate the Earth as well as the other telluric atmospheres in the solar system. Our experience with Mars, Titan and Venus suggests that realistic climate simulators can be developed by combining components like a "dynamical core", a radiative transfer solver, a parametrisation of subgrid-scale turbulence and convection, a thermal ground model, and a volatile phase change code. On this basis, we can aspire to build reliable climate predictors for exoplanets. However, whatever the accuracy of the models, predicting the actual climate regime on a specific planet will remain challenging because climate systems are affected by strong positive destabilizing feedbacks (such as runaway glaciations and runaway greenhouse effect). They can drive planets with very similar forcing and volatile inventory to completely different states.Comment: In press, Proceedings of the Royal Society A 31 pages, 6 figure

La sensibilité sociale : une recension critique

International audienceSocial sensitivity is defined by the adjustment of an organism to the contingencies of social reinforcement (Forget & Rivard, 2010) and relies on the generalized matching law (Baum, 1974) and the operant function of social attention (Sajwaj & Dillon, 1977) such as verbal and non-verbal approvals, staring, proximity (Forget & Otis, 1984). The current article assesses the actual state of knowledge on social sensitivity that has been carried over the last 30 years of research. Studies were identified through a search in PsycInfo regardless of the year of publication. The keywords were matching law, social sensitivity, social attention. The reference section of each article was further examined to identify additional studies on social sensitivity. Inclusion criteria were the use of single-subject designs with social reinforcers and single-subject statistical analyses relying on the generalized matching law. Other studies were rejected because of statistical issues arising from between-subject analyses (Caron, 2013). The current review identified 15 published articles and 4 theses. Results reveal that social sensitivity has been mostly studied on children with Autism Spectrum Disorder and within classroom. Most studies showed that the generalized matching law describes well participants' response allocation according to social reinforcers. Among the 83 identified participants, 57 % conformed to matching law predictions. Results suggest a continuum of social sensitivity. For instance, typical participants' response allocations were generally closer to matching law predictions whereas participants with Asperger syndrome appeared to be insensitive to social reinforcers. Response allocations of the latter population showed low explained variances and a single participant showed a high sensitivity parameter. Participants with Austism Spectrum Disorders ranged between these two groups and showed higher bias value. This result agrees with the idea that this population presents and prefers stereotypic behavior. However, the review shows that 78 % of the identified studies did not use experimental designs. Most studies relied on descriptive observations, that is unconstrained reinforcers ratios, that may lead to relevant issues (St. Peter al., 2005), incorrect outcomes (Thompson & Iwata, 2007) and does not allow definitive conclusions (Bijou, Peterson & Ault, 1968). Considering only experimental designs, a single study showed results in favor of the generalized matching law, another one shows mixed results and the last two cast doubt on the capacity of the generalized matching law to describe social interaction. These ambiguous conclusions clearly point out that more experimental studies are needed. Despite that the flight from natural fields to the laboratory may represent a challenge, it is the next necessary step forward a robust and relevant theory of social sensitivity.La sensibilité sociale se définit comme l'ajustement d'un organisme aux contingences de renforcement social de son environnement (Forget et Rivard, 2010). Ce concept repose sur la loi généralisée de l'appariement (Baum. 1974) et sur l'hypothèse selon laquelle l'attention sociale présente généralement une fonction de renforcement (Sajwaj & Dillon, 1977). La présente recension des écrits empiriques expose les résultats des trente dernières années de recherche sur cette notion de sensibilité. Parmi 83 sujets provenant de 19 études, la fréquence relative des comportements étudiés correspond majoritairement bien aux prédictions de la loi généralisée de l'appariement. Les résultats suggèrent un continuum de sensibilité d'une personne à l'autre, ou d'un type de personnes à l'autre. Ainsi, le comportement des populations tout-venant correspond davantage aux prédictions du modèle tandis que les personnes ayant un syndrome d'Asperger sembleraient insensibles aux renforçateurs sociaux. Par ailleurs, la sensibilité sociale des personnes ayant un trouble du spectre de l'autisme présente une plus grande variabilité, à mi-chemin entre ces deux premiers groupes. Toutefois, 78 % des études n'impliquent aucun contrôle expérimental du taux de renforcement prodigué par l'adulte. Si la loi généralisée de l'appariement semble avoir une valeur heuristique pour déterminer le degré de sensibilité d'une personne à son environnement social, l'établissement de la validité empirique et expérimentale du concept reste à démontrer

ARPES view of orbitally resolved quasiparticle lifetimes in iron pnictides

We study with ARPES the renormalization and quasiparticle lifetimes of the $d_{xy}$ and $d_{xz}$/$d_{yz}$ orbitals in two iron pnictides, LiFeAs and Ba(Fe$_{0.92}$Co$_{0.08}$)$_2$As$_2$ (Co8). We find that both quantities depend on orbital character rather than on the position on the Fermi Surface (for example hole or electron pocket). In LiFeAs, the renormalizations are larger for $d_{xy}$, while they are similar on both types of orbitals in Co8. The most salient feature, which proved robust against all the ARPES caveats we could think of, is that the lifetimes for $d_{xy}$ exhibit a markedly different behavior than those for $d_{xz}$/$d_{yz}$. They have smaller values near $E_F$ and exhibit larger $\omega$ and temperature dependences. While the behavior of $d_{xy}$ is compatible with a Fermi liquid description, it is not the case for $d_{xz}$/$d_{yz}$. This situation should have important consequences for the physics of iron pnictides, which have not been considered up to now. More generally, it raises interesting questions on how a Fermi liquid regime can be established in a multiband system with small effective bandwidths

Increased insolation threshold for runaway greenhouse processes on Earth like planets

Because the solar luminosity increases over geological timescales, Earth climate is expected to warm, increasing water evaporation which, in turn, enhances the atmospheric greenhouse effect. Above a certain critical insolation, this destabilizing greenhouse feedback can "runaway" until all the oceans are evaporated. Through increases in stratospheric humidity, warming may also cause oceans to escape to space before the runaway greenhouse occurs. The critical insolation thresholds for these processes, however, remain uncertain because they have so far been evaluated with unidimensional models that cannot account for the dynamical and cloud feedback effects that are key stabilizing features of Earth's climate. Here we use a 3D global climate model to show that the threshold for the runaway greenhouse is about 375 W/m$^2$, significantly higher than previously thought. Our model is specifically developed to quantify the climate response of Earth-like planets to increased insolation in hot and extremely moist atmospheres. In contrast with previous studies, we find that clouds have a destabilizing feedback on the long term warming. However, subsident, unsaturated regions created by the Hadley circulation have a stabilizing effect that is strong enough to defer the runaway greenhouse limit to higher insolation than inferred from 1D models. Furthermore, because of wavelength-dependent radiative effects, the stratosphere remains cold and dry enough to hamper atmospheric water escape, even at large fluxes. This has strong implications for Venus early water history and extends the size of the habitable zone around other stars.Comment: Published in Nature. Online publication date: December 12, 2013. Accepted version before journal editing and with Supplementary Informatio

ESA's Mars Program: European Plans for Mars Exploration

A viewgraph presentation on the European Space Agency Mars Exploration Program is shown. The topics include: 1) History:Mars Exploration in Europe; 2) A few preliminary results from Mars Express; 3) A new instrument:Radar MARSIS; and 4) European Mars Exploration in the future

Mars Pathfinder meteorological observations on the basis of results of an atmospheric global circulation model

The Mars Pathfinder Meteorological Package (ASI/MET) will measure the local pressure, temperature, and winds at its future landing site, somewhere between the latitudes 0 deg N and 30 deg N. Comparable measurements have already been obtained at the surface of Mars by the Viking Landers at 22 deg N (VL1) and 48 deg N (VL2), providing much useful information on the martian atmosphere. In particular the pressure measurements contain very instructive information on the global atmospheric circulation. At the Laboratoire de Meteorologie Dynamique (LMD), we have analyzed and simulated these measurements with a martian atmospheric global circulation model (GCM), which was the first to simulate the martian atmospheric circulation over more than 1 year. The model is able to reproduce rather accurately many observed features of the martian atmosphere, including the long- and short-period oscillations of the surface pressure observed by the Viking landers. From a meteorological point of view, we think that a landing site located near or at the equator would be an interesting choice

Differences in Water Vapor Radiative Transfer among 1D Models Can Significantly Affect the Inner Edge of the Habitable Zone

An accurate estimate of the inner edge of the habitable zone is critical for determining which exoplanets are potentially habitable and for designing future telescopes to observe them. Here, we explore differences in estimating the inner edge among seven one-dimensional radiative transfer models: two line-by-line codes (SMART and LBLRTM) as well as five band codes (CAM3, CAM4_Wolf, LMDG, SBDART, and AM2) that are currently being used in global climate models. We compare radiative fluxes and spectra in clear-sky conditions around G and M stars, with fixed moist adiabatic profiles for surface temperatures from 250 to 360 K. We find that divergences among the models arise mainly from large uncertainties in water vapor absorption in the window region (10 μm) and in the region between 0.2 and 1.5 μm. Differences in outgoing longwave radiation increase with surface temperature and reach 10–20 W m^(−2); differences in shortwave reach up to 60 W m^(−2), especially at the surface and in the troposphere, and are larger for an M-dwarf spectrum than a solar spectrum. Differences between the two line-by-line models are significant, although smaller than among the band models. Our results imply that the uncertainty in estimating the insolation threshold of the inner edge (the runaway greenhouse limit) due only to clear-sky radiative transfer is ≈10% of modern Earth's solar constant (i.e., ≈34 W m^(−2) in global mean) among band models and ≈3% between the two line-by-line models. These comparisons show that future work is needed that focuses on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models

On thermal effects in solid state lasers: the case of ytterbium-doped materials

A review of theoretical and experimental studies of thermal effects in solid-state lasers is presented, with a special focus on diode-pumped ytterbium-doped materials. A large part of this review provides however general information applicable to any kind of solid-state laser. Our aim here is not to make a list of the techniques that have been used to minimize thermal effects, but instead to give an overview of the theoretical aspects underneath, and give a state-of-the-art of the tools at the disposal of the laser scientist to measure thermal effects. After a presentation of some general properties of Yb-doped materials, we address the issue of evaluating the temperature map in Yb-doped laser crystals, both theoretically and experimentally. This is the first step before studying the complex problem of thermal lensing (part III). We will focus on some newly discussed aspects, like the definition of the thermo-optic coefficient: we will highlight some misleading interpretations of thermal lensing experiments due to the use of the dn/dT parameter in a context where it is not relevant. Part IV will be devoted to a state-of-the-art of experimental techniques used to measure thermal lensing. Eventually, in part V, we will give some concrete examples in Yb-doped materials, where their peculiarities will be pointed out