Jeudi 1er dĂ©cembre 2022 à 16h00 (Salle de rĂ©union du bâtiment 16 et visioconfĂ©rence)
Harry Kenchington Goldsmith (LESIA)
Direct imaging of exoplanets promises the detection of new worlds in the habitable zone around distant stars. Interferometry uses multiple, or one-segmented, telescopes to make direct observations of exoplanets. In the mid-infrared the light of the star outshines the exoplanet by 8 orders of magnitude and interferometry can overcome this by nulling the star. New technologies in photonics may provide a pathway to do this. Photonics is the study of light guided and manipulated within transmissive materials. It has roots in the telecommunication industry and is now being used by astronomers in visible light and near-infrared light, with mid-infrared light to follow in the near future. The basic applications in astronomy are to move away from telescopes with large lab benches and environmentally sensitive fibre optics, to small and stable photonic chips. In this talk I will detail my work in mid-infrared photonics, highlighting the production of evaporatively deposited photonic chips and including specific issues with adapting photonic chips for astronomy applications, with the goal to create a nulling interferometer to detect exoplanets.
Lundi 28 novembre 2022 à 16h00 (Salle de confĂ©rence du bâtiment 17)
Gael DAVID (LESIA)
Les conditions environnementales passĂ©es de la surface de Mars sont accessibles Ă travers les enregistrements gĂ©ologiques de la planète, et plus particulièrement via les minĂ©raux d’altĂ©ration qu’ils contiennent. Ces phases secondaires peuvent constituer de vĂ©ritables marqueurs gĂ©ochimiques des conditions durant l’altĂ©ration aqueuse.
L’instrument ChemCam, Ă bord du rover Mars Science Laboratory (Curiosity) est le premier instrument de spectroscopie sur plasma induit par laser (LIBS) dĂ©ployĂ© Ă la surface de Mars. Il offre un moyen inĂ©dit de caractĂ©riser in situ et Ă une Ă©chelle d’analyse submillimĂ©trique, la composition chimique de la surface de la planète. Durant ce sĂ©minaire, je vais prĂ©senter quelques travaux rĂ©alisĂ©s avec cet instrument sur la dĂ©tection de phases d’altĂ©ration (i.e. sulfates et oxydes de fer) dans les sols et les roches sĂ©dimentaires du cratère de Gale. Leurs processus de formation seront Ă©galement discutĂ©s ainsi que l’histoire gĂ©ologique qui en dĂ©coule.
Lundi 21 novembre 2022 à 16h00 (Salle de confĂ©rence du bâtiment 17)
Oscar Carrion (LESIA)
With more than five thousand exoplanets discovered to date, the next milestone is the atmospheric characterization of a significant number of these worlds. The observing techniques that are currently available have biased the discovery and atmospheric characterization of exoplanets towards hot, giant planets on short-period orbits. Direct-imaging observations will be needed to overcome these biases and enable the analysis of cold and temperate long-period exoplanets and their atmospheres.
Studying this population of planets, which has remained out of reach thus far, is a key to understand the diversity of exoplanets and, in particular, the existence of habitable conditions beyond the Earth. Direct-imaging observations of temperate exoplanets have indeed been identified as a scientific priority for the coming decades both by the US Astro 2020 Decadal Survey and by the ESA Voyage 2050 report. In this talk we address the physical fundamentals of direct-imaging observations in reflected starlight, and derive practical conclusions for the planning and interpretation of the upcoming measurements.
We also analyse the prospects for atmospheric characterization of exoplanets from reflected-starlight spectra with different observing strategies. Finally, we compute which of the known exoplanets are potentially observable with several upcoming direct-imaging space telescopes, and discuss some interesting science cases.
Lundi 10 octobre 2022 à 16h00 (Salle de confĂ©rence du bâtiment 17)
Clément Royer et Lucia Mandon (LESIA)
The Perseverance rover (Mars 2020 mission, NASA) landed in Jezero crater, Mars, the site of an ancient lake, on February 2021. The main science objectives of the mission are the characterization of past environments, the search for preserved biosignatures and the collection of samples to be returned to Earth by the MSR mission (Mars Sample Return). The payload of Perseverance includes the SuperCam instrument, which combines various remote-sensing techniques to investigate the elemental and mineralogical composition of rocks and soils. In particular, the near-infrared reflectance spectrometer (IRS), which covers the 1.3–2.6 µm range, allows for the identification of a wide variety of mineral phases, and especially hydrated ones.
From a technical point of view, IRS is a miniaturized spectrometer based on AOTF (Acousto-Optic Tunable Filter) technology. This optical element is the cornerstone of the IRS’ performance and its flight calibration will be presented in this seminar. Then, we will give an overview of the minerals detected by the IRS during the first year of the mission and the implications on the geological history of the crater floor in terms of igneous and alteration processes. As the IRS is the first near-infrared spectrometer operating directly on the surface of Mars, we will also discuss how these results bring insights into the orbital studies using near-infrared data.
Lundi 3 octobre 2022 à 16h00 (Salle de confĂ©rence du bâtiment 17)
LĂ©a Bonnefoy (Cornell University)
The Selk crater region is the future landing site of NASA’s Dragonfly mission to Titan. The region was imaged by the Cassini RADAR at incidence angles from 5° to 72° and at various polarization angles. Using this data set, we assembled backscatter curves for six terrains. By fitting different models to these data we derived new composition and roughness constraints for each terrain. Topography from radarclinometry also revealed a non-uniform crater rim, less eroded than previously thought.
Jeudi 29 septembre 2022 à 16h00 (Salle de rĂ©union du bâtiment 16 et visioconfĂ©rence)
Anthony BERDEU (LESIA)
Study of astrophysical objects requires always more complex models (black hole surrounding, exoplanet atmosphere, accretion disk, galaxy formation and evolution, …) whose inputs imply always more precise measurements. On the other side, the astronomical instruments start to reach their fundamental limits (negligible sensor readout noise, precise mirror polishing, technologies harder to scale up to extremely large telescopes, …). During my talk, I will discuss how data science applied for optimal data reduction and processing via inverse problem approaches can bridge this gap, by pushing the experimental limits without the need of further instrumental developments. I will introduce different applications of my research : integral field spectroscopy (SPHERE/IFS), blind deconvolution and PSF reconstruction (SPHERE/ZIMPOL) and extreme adaptative optics for coronagraph (Evanescent Wave Coronagraph, EvWaCo).
