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

在过去的二十年里，已经发现了数千颗系外行星，使我们能够大大扩展我们对它们的发生率和体积特性的了解。迄今为止，这些发现已经引发了重大的工作，以改进行星形成和演化的模型，并推动了我们在其他地方寻找生命的探索。在明亮恒星周围运行的系外行星使我们能够透过它们的大气层窥视，我们已经检测到一些分子，并对系外行星大气层的物理条件进行了宽松的限制。然而，我们现有设施所能进行的观测面临着重要的限制。2019年底开始运行的詹姆斯·韦伯太空望远镜（JWST）将彻底改变这一领域。******我是JWST四种仪器之一NIRISS仪器小组的一员，我将利用我们保证的JWST 200小时的观测时间，领导一个项目，利用NIRISS获取16颗系外行星样本的凌日和日食光谱观测，这些行星跨越了平衡温度（300-3000 K）和质量（1地球-10 MJup）的全部可用范围，适合大气表征。我们的观测将测量系外行星大气中存在的分子和气溶胶的丰度，并以前所未有的精度确定它们的垂直和水平温度结构。反过来，这将使我们能够解决一些基本问题，如行星的形成过程及其随后的演化，行星大气中颗粒云的存在和特征，以及可能在其大气中起作用的非平衡化学效应。我们的四个目标是岩石，对于这些目标，我们打算对它们的平均分子量和大气的总体组成进行一些初步的限制。******我也是SPIRou和NIRPS科学小组的一员，这是两台新的高分辨率、光纤馈送、近红外的光谱仪，能够精确测量径向速度。我将使用这些新的强大仪器，利用相对较新的高色散光谱技术来探测系外行星的大气。这些观测结果将与低分辨率的JWST观测结果高度互补，提高我们对大气成分的测定，并提供有关行星大气中气体流动的新信息。利用SPIRou和NIRPS，我还将参与大型径向速度调查，以在太阳附近的低质量恒星周围发现新的岩石行星。这些调查将揭示在不久的将来寻找生物特征的最佳类地行星，考虑到它们明亮的宿主和较短的轨道周期，并将提供一个可靠的确定，即拥有可居住的类地行星的低质量恒星的比例。

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.