New models of Jupiter in the context of Juno and Galileo

Observations of Jupiter's gravity field by Juno have revealed surprisingly small values for the high order gravitational moments, considering the abundances of heavy elements measured by Galileo 20 years ago. The derivation of recent equations of state for hydrogen and helium, much denser in the Mbar region, worsen the conflict between these two observations. In order to circumvent this puzzle, current Jupiter model studies either ignore the constraint from Galileo or invoke an ad hoc modification of the equations of state. In this paper, we derive Jupiter models which satisfy both Juno and Galileo constraints. We confirm that Jupiter's structure must encompass at least four different regions: an outer convective envelope, a region of compositional, thus entropy change, an inner convective envelope and an extended diluted core enriched in heavy elements, and potentially a central compact core. We show that, in order to reproduce Juno and Galileo observations, one needs a significant entropy increase between the outer and inner envelopes and a smaller density than for an isentropic profile, associated with some external differential rotation. The best way to fulfill this latter condition is an inward decreasing abundance of heavy elements in this region. We examine in details the three physical mechanisms able to yield such a change of entropy and composition: a first order molecular-metallic hydrogen transition, immiscibility between hydrogen and helium or a region of layered convection. Given our present knowledge of hydrogen pressure ionization, combination of the two latter mechanisms seems to be the most favoured solution

Corpora and Representativeness Corpora and Representativeness: Where to go from now?

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A complete study of the precision of the concentric MacLaurin spheroid method to calculate Jupiter's gravitational moments

This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this recordA few years ago, Hubbard (2012, 2013) presented an elegant, non-perturbative method, called concentric MacLaurin spheroid (CMS), to calculate with very high accuracy the gravitational moments of a rotating fluid body following a barotropic pressure-density relationship. Having such an accurate method is of great importance for taking full advantage of the Juno mission, and its extremely precise determination of Jupiter gravitational moments, to better constrain the internal structure of the planet. Recently, several authors have applied this method to the Juno mission with 512 spheroids linearly spaced in altitude. We demonstrate in this paper that such calculations lead to errors larger than Juno's error bars, invalidating the aforederived Jupiter models at the level required by Juno's precision. We show that, in order to fulfill Juno's observational constraints, at least 1500 spheroids must be used with a cubic, square or exponential repartition, the most reliable solutions. When using a realistic equation of state instead of a polytrope, we highlight the necessity to properly describe the outermost layers to derive an accurate boundary condition, excluding in particular a zero pressure outer condition. Providing all these constraints are fulfilled, the CMS method can indeed be used to derive Jupiter models within Juno's present observational constraints. However, we show that the treatment of the outermost layers leads to irreducible errors in the calculation of the gravitational moments and thus on the inferred physical quantities for the planet. We have quantified these errors and evaluated the maximum precision that can be reached with the CMS method in the present and future exploitation of Juno's data

A qui profite le crime?

L’histoire témoigne de l’existence de complots. Ils nous invitent à mobiliser notre esprit critique. Mais gardons-nous de croire que tout ce qui est présenté comme vrai est faux et que tout ce qui est présenté comme faux est vrai. Distinguons la croyance en DES complots dans des contextes spécifiques et l’explication de l’histoire comme UN seul et vaste complot (juif, maçonnique…). Pour y voir plus clair, décortiquons, dans cette rubrique, des mécanismes cognitifs et des phrases toutes faites qui doivent éveiller notre attention

Impact of a new H/He equation of state on the evolution of massive brown dwarfs. New determination of the hydrogen burning limit

We have explored the impact of the latest equation of state (EOS) for dense hydrogen-helium mixtures (Chabrier \& Debras 2021), which takes into account the interactions between hydrogen and helium species, upon the evolution of very low mass stars and brown dwarfs (BD). These interactions modify the thermodynamic properties of the H/He mixture, notably the entropy, a quantity of prime importance for these fully convective bodies, but also the onset and the development of degeneracy throughout the body. This translates into a faster cooling rate, i.e. cooler isentropes for a given mass and age, and thus larger brown dwarf masses and smaller radii for given effective temperature and luminosity than the models based on previous EOSs. This means that objects of a given mass and age, in the range M\lesssim 0.1\,\msol, $\tau\gtrsim 10^8$ yr, will have cooler effective temperatures and fainter luminosities. Confronting these new models with several observationally determined BD dynamical masses, we show that this improves the agreement between evolutionary models and observations and resolves at least part of the observed discrepancies between the properties of dynamical mass determinations and evolutionary models. A noticeable consequence of this improvement of the dense H/He EOS is that it yields a larger H-burning minimum mass, now found to be 0.075\,\msol (78.5\,\mjup) with the ATMO atmosphere models for solar metallicity. These updated brown dwarf models are made publicly available.Comment: To appear in Astronomy & Astrophysic

Ne dites plus ‘race’ mais ‘culture’ ou ‘religion’: l’immigration et l’Islam dans les discours des partis d’extrême droite

En raison d’une multiplication des législations visant à interdire l’incitation à la haine raciale ou encore le négationnisme, les discours d’extrême droite ont adapté leur vocabulaire et évitent désormais les termes pouvant être directement reliés aux notions de race, d’inégalité et de hiérarchie. L’argumentaire raciste évolue et effectue un glissement de l’inégalité biologique vers la différence culturelle . La « biologisation » se transforme en « culturalisation », la culture s’érigeant en seconde nature pour les individus . La classification des races humaines s’exprime selon le critère : assimilable versus inassimilabl

Democracy in America

Delivered by François Debras (Jérôme Jamin's substitute for the year 2021-2022), the course aims to teach students the American political system (institutions, mechanisms, actors, values and issues) on both the international and national scene, at both the federal and state levels. The course consists of 8 chapters: I) Introduction, II) The Congress, III) The Presidency (Domestic presidency), IV) The Presidency (Foreign Affairs), V) The Judiciary, VI) Elections, Referendum and Recall, VII) Political parties and electoral sociology, VIII) Campaign finance and pressure groups

Le pseudo-expert et la junk science

Le conspirationnisme n’est pas absent des milieux « savants ». Le phénomène touche tous les secteurs et se retrouve aussi dans des publications scientifiques ou pseudo-scientifiques, également appelées junk science

Démocratie, légitimité et souveraineté

Cous de "Dynamique Démocratique en Europe" sur les notions de démocratie, légitimité et souveraineté. A l'appui, une présentation/analyse de la situation politique et institutionnelle en Hongrie, avec Viktor Orban (Fidesz), les relations entre le pays et l'UE ainsi qu'une analyse du concept de "démocratie illibérale"

Laïcité: outil rhétorique pour l'extrême droite

A partir des années 1990, afin de contourner la législation antiraciste tout en se présentant comme une alternative légitime aux autres formations politiques, les partis d’extrême droite entament une phase de « dédiabolisation » . Si le corpus idéologique demeure inchangé (inégalitarisme, nationalisme et radicalisme), l’argumentaire se modifie. Les discours ne font plus référence aux questions de race mais de culture et de religion. La haine de l’autre se transforme en protection de soi. Les références aux régimes autoritaires ainsi qu’à certaines organisations paramilitaires sont écartées. Les discours se colorent de nouveaux termes, auparavant absents, tels que « égalité homme/femme », « démocratie » ou « laïcité