Probing planet atmospheres and finding small planets nearby: paving the way for detecting life elsewhere

点击翻译按钮获取中文摘要

Thousands of exoplanets have been discovered over the past two decades, enabling us to considerably expand our knowledge of their occurrence rate and bulk properties. The findings to date have triggered significant work to improve models of planet formation and evolution, and fuel our quest to find life elsewhere. The exoplanets caught in transit around bright stars allow us to peek through their atmosphere, and already we have detected a few molecules and placed loose constraints on the physical conditions in exoplanet atmospheres. However, the observations within our reach with current facilities face important limitations. Starting operation in late 2019, the James Webb Space Telescope (JWST) will completely revolutionize this field.******I am a member of the instrument team of NIRISS, one of the four instruments of JWST, and using 200 hours of our guaranteed JWST observing time, I will lead a program to use NIRISS to acquire transit and eclipse spectroscopy observations of a sample of 16 exoplanets that span the full available range of equilibrium temperatures (300-3000 K) and masses (1 MEarth-10 MJup) for planets amenable to atmospheric characterization. Our observations will measure the abundance of the molecules and aerosols present in the exoplanets' atmosphere and determine their vertical and horizontal temperature structure with unprecedented precision. In turn this will allow us to address fundamental issues such as the formation process of planets and their subsequent evolution, the presence and characteristics of particulate clouds in planets' atmosphere, and non-equilibrium chemistry effects that might be at play in their atmosphere. Four of our targets are rocky and for these we intend to place some of the first constraints on the mean molecular weight – and hence bulk composition – of their atmosphere.******I am also a member of the science teams of SPIRou and NIRPS, two new high-resolution, fiber-fed, near-infrared échelle spectrographs capable of precision radial velocity measurements. I will use these new powerful instruments to probe exoplanet atmospheres using the relatively new technique of high dispersion spectroscopy. These observations will be highly complementary to the lower resolution JWST observations, improving our determination of atmospheric composition and providing new information about the flow of gas in the planets' atmosphere. Using SPIRou and NIRPS, I will also participate in large radial velocity surveys to find new rocky planets around low-mass stars in the immediate neighborhood of the Sun. These surveys will uncover the best earth-like planets to search for biosignatures in the near-future, given their bright hosts and short orbital periods, and will provide a robust determination of the fraction of low-mass stars that host a habitable earth-like planet.