Observatoire de Paris Institut national de recherche scientifique français Univerité Pierre et Marie Curie Université Paris Diderot - Paris 7

Sauf exception, les séminaires ont lieu sur le site de Meudon, dans la salle de conférence du bâtiment 17.

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Prochains séminaires

  • Vendredi 1er décembre 2023 à 11h00 (Salle de conférence du bâtiment 17)

    Space Weather : from the interplanetary space to Antarctic

    Sergio Dasso, directeur de recherche et professeur, CONICET et Université de Buenos Aires (FCEN-UBA)

    In this seminar I will present some results about Interplanetary Coronal Mass Ejections, ICMEs. Special emphasis will be made on the main dynamical processes occurring in the interplanetary medium from their solar launching to their arrival to the geo-space. These physical mechanisms can modify the level of ICMEs geoeffectiveness and the ICMEs impact on radiation level at ground level. Finally, I will briefly present a new Space Weather laboratory in an Argentine base at the Antarctic peninsula, from where the variability (e.g., the variaility produced by ICMEs near Earth) of the galactic cosmic rays flux at ground level can be observed in real time.

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Séminaires passés

  • Lundi 27 novembre 2023 à 15h00 (Salle de conférence 204 du bâtiment 18)

    "Atelier nuages : LESIA’s approaches on modelling and characterizing clouds in planetary atmospheres"

    Óscar Carrión-González et Pablo Rodríguez-Ovalle, post-doctorant et doctorant au pôle planétologie

    Clouds and hazes are ubiquitous in the planetary atmospheres observed in the Solar System and beyond. Characterizing the properties of these aerosol layers provides unique information about the atmospheric structure and composition of a planet. However, the aerosol’s optical properties are generally correlated with those of other atmospheric components and even with non-atmospheric parameters of the planet. Accurately modelling clouds and hazes is thus a key to accurately characterizing (exo)planetary atmospheres.

    In this Théminaire ( 1h30 duration) we will have an open discussion on the different approaches taken at LESIA to model clouds and hazes in the atmospheres of Solar-System and extrasolar planets, and even retrieve chemical information on their nature. Several speakers have confirmed short presentations : Benjamin Charnay, Sandrine Vinatier, Joan Roy-Pérez (visiting from UPV/EHU, Spain), Óscar Carrión-González, Pablo Rodríguez-Ovalle, Lucas Teinturier. Additional speakers are welcome, and we warmly invite them to contact : oscar.carrion obspm.fr or pablo.ovalle obspm.fr to keep track of the planned duration.

    Lien pour assister au séminaire :

  • Lundi 20 novembre 2023 à 16h00 (Salle de conférence 207, bâtiment 16)

    Planet-gas interactions in debris discs : Observable outcomes

    Camille Bergez-Casalou, post-doctorante au pôle planétologie

    Since recently, consequent amounts of CO gas were observed in old debris disks which were expected to be gas-free. At this stage, planet formation already occurred and fully formed planets are expected to be evolving in these disks. In this presentation, I will show how these planets might form observable substructures in the gas of these debris disks. When a planet is embedded in a gas disk, it perturbs its normally keplerian velocity. The resulting perturbation, called a kink, has been observed in protoplanetary disks. I use hydrodynamical simulations with the FARGO3D code to estimate the structure of typical debris disks perturbed by the presence of planets of different characteristics (masses and locations). With the help of the radiative transfer code RADM3D coupled to the observing tool CASA, I am able to derive realistic ALMA synthetic images of the disks’ gas emission and show under which conditions these features can also be observed in debris disks. We find that, if the planet is far away in the disk and at least as massive as Jupiter, then such kinks can be observed. Some known debris disks are therefore ideal candidates to search for such perturbations. This method can lead to a new way to indirectly detect exoplanets at an intermediate stage during their formation.

    Lien pour assister au séminaire :

  • Lundi 20 novembre 2023 à 10h00 (Salle 103a, bâtiment 14 et visioconférence. Attention horaire et jour inhabituel)

    Significance of Meso-scale Structures in Ionosphere-Thermosphere System

    Yue Deng, Professor in the Department of Physics at the University of Texas at Arlington

    Space environment includes Sun, Solar wind (a.k.a. heliosphere), magnetosphere and ionosphere-thermosphere (a.k.a. upper atmosphere). The geomagnetic storms can be triggered by the activities on the Sun and in the heliosphere, which can strongly influence the coupling between magnetosphere and ionosphere, and the energy deposited into the upper atmosphere. The impact of geomagnetic storms on our geospace environment and society is the primary focus of space weather action. The typical space weather impacts include changing satellite orbits through increasing atmospheric drag, damaging the power lines and pipelines through geomagnetically induced currents (GICs), influencing the GPS and high-frequency (HF) communications through ionospheric variations.

    A recent significant change in our understanding of the ionosphere-thermosphere system is the frequent driving by dynamic meso-scale structures (50 km - 500 km) that couple to the magnetosphere in the polar cap region, the dayside cusp and along auroral oval and sub-auroral magnetic field lines. These structures play a critical role in Space Weather dynamics, interacting with the more slowly changing, large-scale structure that is more directly driven by interaction with the solar wind. The Global Ionosphere Thermosphere Model (GITM), a self-consistent non-hydrostatic model in the upper atmosphere with a flexible resolution, is suitable for studying transient meso-scale phenomena. To improve the description of meso-scale structures in geomagnetic forcing and to evaluate the influence of such structures on the global dynamics of the upper atmosphere, various data and models are utilized to investigate the variations of energy inputs in the cusp, sub-auroral regions and within flow bursts, and their influences on the coupled thermosphere-ionosphere system.

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  • Lundi 6 novembre 2023 à 16h30 (Salle de conférence 207 du bâtiment 16)

    Laboratory investigations of Phobos spectral simulants : effects of porosity and geometry

    Antonin Wargnier, doctorant du pôle planétologie

    The origins of Phobos and Deimos – the two martian moons – remain uncertain. Two main hypotheses are currently suggested to explain their formation. The first proposes that Phobos and Deimos could have been formed by a giant impact between Mars and a protoplanet. The other hypothesis posits that Phobos and Deimos may be captured asteroids.

    JAXA Martian Moon eXploration (MMX) mission – will be crucial in this context to unveil Phobos and Deimos origins. MMX will be the first sample return mission dedicated to the biggest martian moon, Phobos. The composition of Phobos will also be studied, by the infrared spectrometer MIRS. In particular, MIRS will be able to observe Phobos at 3.4 µm organics (0.9-3.6 µm). Detectability of this feature is expected in the case of captured asteroid hypothesis.

    In support of the MMX mission, we searched to develop a Phobos visible, near- and mid-infrared spectroscopic laboratory simulant. We studied the detection of organic compounds in a Phobos simulant to support the interpretation of future MIRS observations. Furthermore, surfaces of small bodies are generally covered by fine-grained porous regolith. Therefore, we conducted laboratory experiments to analyze the spectroscopic effects of porosity on a Phobos simulant, by creating porous samples with sublimation of water ice mixed with grains of the Phobos simulant. This presentation will show the results of our laboratory investigations on Phobos simulants.