PLATO: assessment phase and community preparation - Final Version

PLATO（行星凌日和恒星振荡）使命与其他三个M级候选飞行任务沿着被选定在欧空局宇宙观方案框架内进行评估研究。该项目因其重要和引人注目的科学目标以及相对较低的技术风险而被列入短名单。PLATO的主要科学目标是研究系外行星系统，方法是探测和测量大量明亮恒星样本前的系外行星测光凌日，并充分描述行星及其宿主恒星的特征。特别是，这种表征将包括对行星宿主恒星的地震分析，提供对宿主恒星的质量，半径和年龄的准确和可靠的测量，从而使我们能够测量检测到的系外行星的类似数量。经典的恒星表征方法，基本上是基于它们在HR图中的精确位置及其与计算的演化轨迹和等时线的比较，无法提供所需的准确可靠的恒星参数。质量不可能超过15%，而主序星的年龄基本上仍然无法确定。因此，新的调查，如对系外行星宿主恒星的地震分析，是在这一领域取得进展所必需的。目前的MOST、CoRoT、Kepler（以及候选的SMEX使命TESS）任务有望为我们了解系外行星系统带来重要成果，但在监测的恒星数量、最小行星尺寸、最大轨道周期、星震学频率测量精度等方面受到限制。PLATO作为这些开创性实验之后的下一代使命，将克服这些限制，并为我们提供更好，更深入的调查工具，用于研究系外行星及其演化的统计数据，以及恒星结构和演化。因此，PLATO将为我们提供一个前所未有的完全特征化的系外行星样本，并对其质量、大小和年龄进行准确可靠的测量，从而可以研究系外行星系统的形成和演化。此外，由于PLATO将搜索围绕明亮恒星运行的行星，它将提供关键目标列表，包括地球模拟系统，用于进一步研究行星，理想的是未来的地面和空间日冕和/或干涉测量设施（如ELT）和生物标记的光谱搜索。这种能力使PLATO成为STFC交付计划/路线图和ESA路线图中关于地球模拟系统发生和生命出现的声明的中心。在本建议书中，我们为PLATO A阶段的资金投标。英国社区在PLATO理事会（3名成员）中有很好的代表性，并且是获得科学联盟PI（或至少共同PI）的有力竞争者。因此，我们在实验本身的设计和实施方面具有影响力。在英国，我们需要准备系外行星和小行星学社区参与使命，因为充分利用数据集需要大量的准备和组织。在技术方面，我们的努力将集中在我们已经可以声称具有一定领导地位的领域，即CCD的采购和特性鉴定、焦平面的设计和建造以及数据分析和存档。由于欧空局的爱丁顿使命（具有类似复杂的焦平面）、盖亚数据管道和广角行星搜索（WASP）存档和过境搜索软件的大量准备工作，我们可以在每一个方面都拥有相当多的相关经验。

The PLATO (PLAnetary Transits and Oscillations of stars) mission was selected along with three other M-class mission candidates for an assessment study in the framework of the ESA Cosmic Vision programme. It was short listed because of its important and high profile scientific objectives and its comparatively low technical risk. PLATO's main scientific goal is to study exoplanetary systems, by detecting and measuring exoplanet photometric transits in front of a large sample of bright stars, and by fully characterizing the planets and their host stars. In particular, this characterization will include seismic analysis of the planet host stars, providing accurate and reliable measurements of the masses, radii and ages of the host stars, hence allowing us to measure similar quantities for the detected exoplanets. Classical methods for characterizing stars, essentially based on their precise location in the HR diagram and its comparison with computed evolutionary tracks and isochrones, fail to provide the accurate and reliable stellar parameters that are needed. Masses cannot be known to better than 15%, while ages remain essentially undetermined for main sequence stars. New investigations, such as seismic analysis of exoplanet host stars, are therefore necessary to progress in this area. The current crop of missions MOST, CoRoT, Kepler (and the candidate SMEX mission TESS) are expected to bring essential results in our understanding of exoplanetary systems, but suffer limitations in terms of number of stars monitored, minimum planet size, maximum orbital period, precision in frequency measurements for asteroseismology. PLATO, as a next-generation mission after these pioneering experiments, will overcome these limitations, and provide us with a much better, much deeper investigation tool for studying the statistics of exoplanets and their evolution, as well as stellar structure and evolution. PLATO will therefore provide us with an unprecedented sample of fully characterized exoplanets, with accurate and reliable measurements of their masses, sizes and ages, from which exoplanetary system formation and evolution can be studied. Also, because PLATO will search for planets orbiting bright stars, it will provide key target lists, including earth analog systems, for further studies of planets, ideal for future ground- and space-based coronographic and/or interferometric facilities (eg ELT) and spectroscopic searches for bio-markers. This ability places PLATO central to statements in the STFC Delivery Plan/Roadmap and ESA Roadmap concerned with the occurrence of earth analogue systems and the emergence of life. In this proposal we bid for funding for the PLATO Phase A. The UK community is well represented on the PLATO Council (3 members) and are serious contenders for obtaining the PI for the Science Consortium (or at least co-PI). Hence we are influential in the design and implementation of the experiment itself. Within the UK we need to prepare both the exoplanet and asterosiesmology communities to engage with the mission as a significant level of preparation and organisation will be needed to fully exploit the datasets. On the technology front our efforts will concentrate on areas that we can already claim some leadership ie CCD procurement and characterisation, the design and construction of the focal plane, and data analysis and archiving. In each of these we can claim considerable relevant experience due to significant preparatory work for ESA's Eddington Mission (which had a similarly complex focal plane), the Gaia data pipeline and the Wide Angle Search for Planets (WASP) archive and transit search software.