Planets Through Time: Understanding the Evolution and Diversity of Planetary Systems

到目前为止，已经发现了4000多颗系外行星，未来几年还将有更多的系外行星被发现，我们正经历着一个系外行星发现的黄金时代。我们现在知道，行星系统在其性质上表现出广泛的多样性，我们自己的太阳系并不典型。例如，我们发现了像木星这样的行星，它们的轨道只有几天（所谓的“热彗星”），行星系统包含多个小行星，它们的轨道都比水星小，也许最令人惊讶的是，我们发现地球和海王星之间的行星是最常见的，但我们自己的太阳系中没有这样的类似物。控制行星系统如何发展成我们观察到的多样化种群的过程被认为发生在它们形成后的第一个十亿年。由于已知的系外行星通常绕着像我们的太阳这样的老恒星运行，这些恒星已经有10亿多年的历史了，因此很难解开驱动它们早期演化的过程，因为这些过程已经完成。为了了解行星系统的早期演化，我们需要探测仍处于演化过程中的年轻行星;这是我们计划的目标。凌日行星，其轨道平面与地球对齐，使它们周期性地通过（即过境）其宿主星星的前面，是最有价值的，因为它们可以被最详细地研究。我们将在两个主要系外行星调查的组合数据集中寻找年轻的凌日行星，下一代凌日调查（NGTS）和凌日系外行星调查卫星（TESS）。我们探测到的年轻行星将帮助我们了解推动行星系统早期演化为我们观察到的多样化种群的过程。它们还将提供（i）我们的行星形成和早期进化理论与（ii）已知（旧）系外行星种群之间的联系。此外，它们还将帮助我们了解系外行星本身的一些内在属性，例如为什么一些热彗星看起来比我们预期的要大，为什么缺乏轨道周期短、大小不到地球两倍的行星。最后，迄今为止发现的大多数凌日行星被认为是从它们形成的地方向它们的主星星迁移的。在我们的太阳系中没有发生过如此重大的迁移。最终，这项工作将帮助我们了解观测到的过境行星系统的多样性，以及为什么看似无处不在的迁移过程在我们的太阳系中没有进展。

With over 4000 exoplanets discovered to date, and many more expected in the coming years, we are living through a golden age of exoplanet discovery. We now know that planetary systems exhibit a wide diversity in their properties, and that our own Solar System is not typical. For example, we have found planets like Jupiter on orbits of only a few days (so called "hot Jupiters"), planetary systems containing multiple small planets on tightly packed orbits that are all smaller than Mercury's and, perhaps most surprising of all, we have discovered that planets with sizes between those of the Earth and Neptune are the most common, yet we have no such analogues in our own Solar System. The processes that govern how planetary systems develop into the diverse population that we observe are thought to occur during the first billion years after their formation. As known exoplanets typically orbit old stars like our Sun, which are more than a billion years old, it is difficult to unravel the processes that drove their early evolution as these processes have already finished. To understand the early evolution of planetary systems, we need to detect young planets, which are still in the processes of evolving; this is the aim of our programme. Transiting planets, whose orbital plane aligns with Earth so that they periodically pass in front of (i.e. transit) their host star, are the most valuable as they can be studied in greatest detail. We will search for young transiting planets in the combined dataset of two leading exoplanet surveys, the Next Generation Transit Survey (NGTS) and the Transiting Exoplanet Survey Satellite (TESS). The young planets that we detect will help us to understand the processes that drive the early evolution of planetary systems into the diverse population that we observe. They will also provide a link between (i) our theories of planet formation and early evolution and (ii) the known (old) exoplanet population. Furthermore, they will help us to understand some intrinsic properties of exoplanets themselves, such as why some hot Jupiters appear to be larger than we expect, and why there is a dearth of planets on short orbital periods that are just under twice the size of Earth.Finally, the majority of transiting planets detected to date are thought to have migrated from where they formed in towards their host star. Such significant migration did not occur in our Solar System. Ultimately, this work will help us to understand the observed diversity of transiting planet systems, as well as why the seemingly ubiquitous migration process did not progress in our Solar System.