The exploration of Jupiter’s and Saturn’s system respectively by Galileo (1996-2003) and Cassini-Huygens (2004-2017), has revealed that several moons around Jupiter (Europa, Ganymede, Callisto) and around Saturn (Titan, Enceladus, Mimas) harbor a subsurface salty ocean underneath their cold icy surface. By flying through the icy-vapor plume erupting from Enceladus’ south pole, Cassini proceeded for the first time to the analysis of fresh materials coming from an extraterrestrial ocean. These analyses revealed that Enceladus possess all the ingredients for the emergence of life. Even if there is no direct evidence yet, similar ingredients might also be present within Europa, Ganymede and Titan, which will be characterized by future exploration missions currently under development at ESA (JUICE) and NASA (Europa Clipper, Dragonfly).
Even if the astrobiological potential of these ocean worlds are very promising, at the exception of Enceladus, their oceanic environments are still poorly known. In this seminar, after giving an overview of the current knowledge on these ocean moons, I will present how future exploration and laboratory works will allow us to better determine the physico-chemical conditions of their subsurface oceans. In particular, I will discuss the possible occurrence of active aqueous processes on these bodies and the implications for the habitability of their subsurface oceans. Finally, I will discuss how the numerical models and experiments developed for ocean moons can be used to characterize the physico-chemical evolution of water-rich exoplanets that we are just starting to unveil.
Gabriel Tobie, Laboratoire de Planétologie et Géodynamique, CNRS/Univ. Nantes
The workhorse instruments of the current 8-10m class observatories are multi-object spectrographs (MOS), providing comprehensive follow-up of ground-based and space-borne imaging data. With the advent of even deeper imaging surveys from, e.g., HST, VISTA, JWST and Euclid, many science cases require complementary spectroscopy with high sensitivity and good spatial resolution to identify the objects and to measure their astrophysical parameters. The light-gathering power of the 39m ELT and its spatial resolution, combined with a MOS, will enable the large samples necessary to tackle some of the key scientific drivers of the ELT project, ranging from studies of stellar populations out to the highest-redshift galaxies. Consequently, a MOS-facility is foreseen within the ELT instrumentation plan.
I will first and briefly describe MOSAIC prominent Science Cases and, then, enter into some details of the instrument conceptual design as available now at the end of phase A. I will discuss the present management of the project and will describe the way we are foreseeing the fabrication phase including the design phase towards the Final Design Review (FDR).
I will end the presentation by listing the main issues that are pending now and will have to be sorted out before Phase B starts (January 2019).
Since circumstellar dust in debris disks is short-lived, dust-replenishing requires the presence of a reservoir of planetesimals which continuously supply the disk with fine dust through their mutual collisions. In this talk I will summarize selected studies related to the properties of this dust and the structure of debris disks on various scales.
Introduction to Supervised Regression and Classification with Machine Learning Methods
Observations of Galactic dust are a highlight and a lasting legacy of the Planck space mission.
Spectacular images combining the intensity of dust emission with the texture derived
from polarization data have received world-wide attention and become part of the general scientific
knowledge. Beyond this popular success, the dust maps are an immense step forward
for Galactic astrophysics, greatly superseding earlier observations. Planck has provided us with the data
needed to statistically characterize the structure of the Galactic magnetic field and its coupling with
interstellar matter and turbulence. Planck multi-frequency observations have also opened a new perspective
on interstellar dust, upsetting existing models. Futrhermore, the astrophysics of dust emission has
become inter-connected to a paramount objective of observational cosmology: the quest for curl-like
(B-mode) polarization of the cosmic microwave background expected to arise from primordial
gravitational waves produced during the inflation era in the very early Universe. I will introduce
these science topics and highlight key results and perspectives of on-going research.
Francois Boulanger
Ecole Normale Superieure, Paris, France
Les grands relevés spectroscopiques (Gaia-ESO, APOGEE, LAMOST, GALAH) apportent des contraintes sur les propriétés de surface des étoiles, y compris leur composition chimique. Depuis une dizaine d’années, l’astérosismologie (CoRoT, Kepler) ajoute des contraintes supplémentaires en sondant les intérieurs stellaires. D’autre part, le satellite Gaia commence à fournir des parallaxes et des données astrométriques avec une précision inégalée.
La diversité et la variété des grands relevés actuels ouvrent donc de nouvelles perspectives pour comprendre l’histoire de notre Galaxie, reposant sur une meilleure compréhension de la physique stellaire, et ceci pour toutes les populations d’étoiles
La synthèse de populations stellaires est une méthode puissante pour exploiter au mieux la synergie de ces données. Nous avons perfectionné le modèle de la Galaxie de Besançon (BGM) en incluant des modèles d’évolution stellaire, calculés avec STAREVOL, pouvant suivre les propriétés chimiques et sismiques des étoiles au cours de leur vie. Nous montrons ici les premières comparaisons du BGM avec les abondances de surface du carbone et de l’azote d’étoiles géantes de Gaia-ESO pour illustrer l’effet des mécanismes de transport dans les étoiles géantes. En particulier nous montrons que les hypothèses de physique stellaire ont un impact très important sur la détermination des âges, l’un des paramètres piliers pour l’archéologie galactique.
Cette approche prometteuse pourra être appliquée pour tester d’autres processus physiques importants pour la physique stellaire (diffusion atomique, rotation, binarité). Ces modèles fourniront des méthodes de datation des étoiles robustes et applicables à grande échelle dans la Voie Lactée.