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

  • Mardi 27 fĂ©vrier 2024 à 16h00 (Salle de confĂ©rence du bâtiment 17)

    The polar regions of Jupiter

    Vincent HUE (Laboratoire d’Astrophysique de Marseille)

    The polar atmosphere of Jupiter is a complex region were chemistry, dynamics and magnetospheric-coupling are intertwined. Several decades of ground-based observations and spacecraft measurements (Voyager, Cassini, Juno) are progressively revealing how rich and complex these regions are. Species such as HCN, CO, H2O were brought in large amount during the Shoemaker-Levy 9 impact in 1994 and provide important dynamical tracers, as they have spread across the atmosphere over the last 30 years. Hydrocarbons originate from methane-photolysis and are affected by auroral precipitations, leading to the formation of aerosols across the polar cap. Magnetosphere-ionosphere coupling generates powerful electrojets that drag the neutral stratosphere underneath. I will review our current understanding of these regions, based on observations from Cassini, Juno, ALMA, Gemini, and IRTF.

  • Lundi 19 fĂ©vrier 2024 à 16h00 (Salle de confĂ©rence du bâtiment 17)

    Timing of Explosive Volcanic Eruptions on Mercury

    Mireia LEON-DASI (LESIA)

    Volcanism plays a major role in Mercury’s geological processes, and understanding this activity is crucial to delimit the evolution of the planet. The presence of large pyroclastic deposits contrasts with formation models which predict a volatile depleted crust and mantle, especially in the recent past. Constraining the timing of these volcanic eruptions and the extent of the resulting pyroclastic deposits is fundamental to refine our knowledge of Mercury’s internal evolution and improve the formation models. Using a Deep Learning approach with MESSENGER/MASCS spectra we delimit the extent of irregular pyroclastic deposits and update the area of these features. Moreover, we study the evolution of the spectral properties of pyroclastic deposits over time, using the degradation state of the vent as a reference for the deposit age. We observe a trend between the deposit spectra and the vent degradation characterized by a rapid initial darkening and flattening over time followed by stabilization. The oldest deposits reach a steady state with no further spectral changes. To explain these temporal variations in spectral properties, we propose three potential processes : space weathering, mixing with the background and changes in pyroclast size over time. We examine the implications of space weathering on spectral properties and discuss the eruption timeline for each scenario. Finally, we introduce the ongoing lab measurement campaign to study the effect of grain size and composition on the spectral properties of Mercury analogs, with the aim of improving our knowledge of how different processes can affect the spectra of this planet.

  • Lundi 12 fĂ©vrier 2024 à 16h00 (Salle de confĂ©rence du bâtiment 17)

    Deciphering Remote Sensing Data from Micro- to Macro-Scale : Infrared Laboratory Investigations in Support of Solar System Exploration

    Giovanni Poggiali (LESIA)

    Several Solar System bodies target of past, present and future space missions are characterized by dark rocky surfaces and complex mixtures of several component with different grain size regolith material. Space missions with their payloads of scientific instrumentation are our gateway to the knowledge of these surfaces, and in recent years the gap is being further closed with the study of samples returned to Earth. Meanwhile, analyzing analogous materials, like minerals mixtures and meteorites, remains one of the pivotal laboratory investigations to support remote sensing interpretation. It also represents one of the most challenging experiments, in particular when multiple components are used in the mixtures. We will review briefly the state of art of laboratory investigations and present in several results from different works that share the common goal of studying how the complex mixing of different grain size and dark materials can affect the behavior of infrared spectra in the near- to mid-infrared range (1.25-25 ÎĽm).

  • Lundi 22 janvier 2024 à 16h00 (Salle de confĂ©rence du bâtiment 17)

    Mercure : une surface volcanique soumise Ă  l’altĂ©ration spatiale

    Emma Caminiti, doctorante du pôle planétologie

    La surface de Mercure est soumise Ă  l’altĂ©ration spatiale de par l’absence d’atmosphère dense. Le bombardement mĂ©tĂ©oritique, l’irradiation du vent solaire, les tempĂ©ratures extrĂŞmes ainsi qu’un volcanisme intense ont fortement modifiĂ©s la surface au cours du temps. Les donnĂ©es spectrales obtenues par la mission NASA/MESSENGER ont permis de mieux contrainte l’évolution de la surface de Mercure ; cependant les propriĂ©tĂ©s spectrales ont grandement Ă©tĂ© influencĂ©es par l’irradiation solaire pouvant induire un biais lors de leur interprĂ©tation. Des expĂ©riences de laboratoire simulant l’irradiation du vent solaire permettent de contraindre les changements spectraux liĂ©s Ă  l’environnement. Une meilleure comprĂ©hension du rĂ´le de l’altĂ©ration spatiale sur les propriĂ©tĂ©s spectrales est essentielle aux vues de l’arrivĂ©e imminente de la sonde ESA/JAXA/BepiColombo.

    Mercury’s surface is subject to space weathering due to the absence of a dense atmosphere. Meteorite bombardment, solar wind irradiation, extreme temperatures and intense volcanism have intensely modified the surface over time. The spectral data obtained by the NASA/MESSENGER mission have enabled us to better constrain the evolution of the surface however, the spectral properties have been greatly influenced by solar irradiation, which can lead to a bias in their interpretation. Laboratory experiments simulating solar wind irradiation are used to constrain spectral changes induced by the environment. A better understanding of the role of space weathering on spectral properties is essential in preparation for the imminent arrival of the ESA/JAXA/BepiColombo mission.

  • Lundi 11 dĂ©cembre 2023 à 16h00 (Salle de confĂ©rence 204 du bâtiment 18)

    Observations de notre planète Terre par radiomĂ©trie microonde : caractĂ©risation de sa surface et de son atmosphère

    Catherine Prigent (LERMA / Observatoire de Paris-PSL)

    L’observation de la Terre par radiométrie microonde depuis les satellites fournit des données essentielles pour la météorologie et l’étude des océans, des glaces, des continents. Le groupe télédétection du LERMA a développé une expertise dans ce domaine, allant du transfert radiatif à la production d’algorithmes d’inversion de paramètres géophysiques pour la climatologie. On donnera quelques exemples d’études récentes au LERMA, en insistant sur les thématiques d’intérêt en planétologie.

    On montrera aussi comment l’Europe a investi récemment dans ces observations microondes passives pour l’observation de la Terre, avec le lancement de plusieurs instruments innovants d’ici la fin de la décennie.

  • Vendredi 8 dĂ©cembre 2023 à 10h30 (Salle 103a du bâtiment 14)

    The Plasma Observatory mission

    Karine Issautier (LESIA)

  • Vendredi 1er dĂ©cembre 2023 à 11h00 (Salle de confĂ©rence 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.

  • Lundi 27 novembre 2023 à 15h00 (Salle de confĂ©rence 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 ThĂ©minaire ( 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-PĂ©rez (visiting from UPV/EHU, Spain), Ă“scar CarriĂłn-González, Pablo RodrĂ­guez-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.

  • Lundi 20 novembre 2023 à 16h00 (Salle de confĂ©rence 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.

  • Lundi 20 novembre 2023 à 10h00 (Salle 103a, bâtiment 14 et visioconfĂ©rence. 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.