PLATO: assessment phase and community preparation - Final Version

柏拉图(行星凌日和恒星振荡)飞行任务与其他三个M级候选飞行任务一起被选为欧空局宇宙远景方案框架内的一项评估研究。它之所以入围，是因为它的重要和高调的科学目标，以及相对较低的技术风险。柏拉图的主要科学目标是研究系外行星系统，通过在一大批明亮的恒星面前探测和测量系外行星的光度凌日，并通过充分描述行星及其宿主恒星的特征。特别是，这一特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探测到的系外行星的类似数量。描述恒星特征的经典方法，基本上是基于它们在HR图上的精确位置，以及它与计算的演化轨迹和等时线的比较，无法提供所需的准确和可靠的恒星参数。质量不可能超过15%，而主序星的年龄基本上仍然没有确定。因此，有必要进行新的研究，如系外行星宿主恒星的地震分析，以便在这一领域取得进展。目前的MOST、CoRoT、开普勒(以及候选的SMEX任务TESS)任务预计将在我们对系外系的理解方面带来基本结果，但在监测的恒星数量、最小行星尺寸、最大轨道周期、星震学的频率测量精度方面受到限制。因此，柏拉图将为我们提供一个史无前例的、充分描述系外行星特征的样本，对它们的质量、大小和年龄进行准确和可靠的测量，从中可以研究系外行星系统的形成和演化。此外，由于柏拉图将搜索围绕明亮恒星运行的行星，它将提供关键目标清单，包括地球模拟系统，用于进一步研究行星，这是未来地面和空间日冕和/或干涉设施(例如ELT)和光谱搜索生物标记的理想选择。这种能力使柏拉图在STFC交付计划/路线图和欧空局路线图中关于地球模拟系统的发生和生命的出现的陈述中处于核心地位。因此，我们在实验本身的设计和实施中具有影响力。在英国，我们需要准备好系外行星和小行星地震学社区参与这项任务，因为需要进行大量的准备和组织，以充分利用数据集。在技术方面，我们的努力将集中在我们已经具有一定领导地位的领域，即电荷耦合器件的采购和特性、焦平面的设计和建造以及数据分析和归档。

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.