Finding a second Earth through stellar understanding

几个世纪以来，包括我在内的人们一直在想，我们是否在宇宙中是孤独的。仅仅在30年前，就发现了第一颗绕太阳以外的恒星运行的行星。这些新发现的星球被称为系外行星。在过去的三十年里，我们见证了已知系外行星数量的指数增长，到目前为止已经发现了5000多颗。这表明系外行星无处不在，大小和结构各不相同。与此同时，还没有发现真正类似地球的行星或类似太阳系的行星系统。我的项目将首次能够找到一颗类似地球的行星，绕着一颗类似太阳的恒星运行。系外行星可以通过观测和模拟其所在恒星的引力摆动来探测，这可以从它们随时间变化的径向速度中看到。此外，利用径向速度变化的技术是目前唯一可行的测量小系外行星质量的方法。不幸的是，对于像地球这样的小型长周期系外行星，这些速度变化远远低于恒星引起的径向速度变化。这些恒星信号是由于恒星磁场的表面可变性，从而淹没了来自遥远系外行星的较小信号。我将提高我们测量和提取小型系外行星微小信号的能力。这将通过考虑光谱数据中恒星磁场的可变性来实现。我将使用我们已知的最亮的恒星太阳作为一颗测试星来开发处理恒星数据的新技术。除去太阳系中已知行星的影响，太阳可以充当唯一一颗我们确定数据中没有行星信号的已知恒星。这创造了一个独特的机会，在将新技术应用于其他恒星之前，测试和改进它们。作为未来领导者研究员，我将扩大我们的仪器能力，研究太阳作为恒星，并描述在其他恒星周围发现的小型系外行星的特征。作为该项目的一部分，我将建造和开发一台新的太阳望远镜，以测量稳定的径向速度和太阳磁场的同步变化。这台独特的仪器将是同类仪器中第一台具有偏振能力的仪器，它将为发现更小、更远的系外行星开辟道路。为了将地球和太阳系置于整个系外行星种群的背景下，我将研究恒星和行星组成之间的联系。我可以使用我的项目中已经使用的相同的光谱数据来寻找和描述系外行星。通过准确地描述系外行星系统的整体特征，我们将深入了解行星形成和演化的具体细节，以及在其他行星上存在生命的可能性。这将使我们更接近于了解我们在宇宙中的位置以及地球可能是多么独特。

People, including me, have wondered for centuries if we are alone in the Universe. Only a mere thirty years ago, the first planet orbiting a star other than the Sun was discovered. These newly discovered worlds were called exoplanets. Over the last three decades we have witnessed an exponential rise in the number of known exoplanets, with more than 5000 discovered so far. This has shown that exoplanets are ubiquitous and come in various sizes and architectures. At the same time, a planet truly resembling Earth or a planetary system resembling the Solar System, has not yet been discovered.My project will for the first time enable to find a planet resembling Earth orbiting a star resembling the Sun. Exoplanets can be detected by observing and modelling the gravitational wobble of their hosting star, seen in their changing radial velocities over time. Furthermore, the technique of using radial velocity changes is currently the only viable way of measuring the mass of small exoplanets. Unfortunately, for small long-period exoplanets such as Earth, these velocity changes are well below the stellar-induced changes in the radial velocity. These stellar signals are due to the surface variability of the stellar magnetic field and thus drown out the smaller signals from far-away exoplanets.I will improve our ability to measure and extract the tiny signals of small exoplanets. This will be done by accounting for the stellar magnetic field variability in the spectroscopic data. I will use our brightest known star, the Sun, as a teststar to develop new techniques to deal with the stellar data. Removing the effect of the known planets in the Solar System, the Sun can act as the only known star where we are certain there are no planetary signals in the data. This creates a unique opportunity to test and improve new techniques before using them on other stars.As a Future Leader Fellow, I will expand our instrumental capacities to study the Sun-as-a-star and characterise the small exoplanets found around other stars. As part of the project, I will build and exploit a new Solar Telescope to measure both stable radial velocities and the simultaneous changes in the Solar magnetic field. This unique instrument would be the first of its kind to have polarimetric capabilities that will open the pathway to discovering smaller and more distant exoplanets.To place Earth and the Solar System into the context of the full exoplanet population, I will study the connection between stellar and planetary composition. I can do this using the same spectroscopic data used already in my project to find and characterise the exoplanets. By accurately characterising exoplanet systems as a whole, we will gain insight into the specific details of planet formation and evolution and the possibilities for existence of life on other planets. This will bring us one step closer to understanding our place in the Universe and how unique Earth could be.