INNATE Investigating the nature and origins of exoplanets in the Neptunian desert

自从25年前51Peg b被发现以来，我们对系外行星的认识经历了一步的变化。行星现在很常见，大多数恒星都有行星系统。在已知的4300多颗行星中，从行星的大小、组成和宿主星的性质方面，可以看到行星分布的趋势和差距，这些趋势和差距源于塑造这些世界的形成和演化过程。行星分布的一个显著特征是海王星沙漠，即缺乏类似海王星的行星围绕其宿主恒星运行。距离恒星如此之近的行星要么被蒸发掉，要么完全被恒星的强大引力破坏。然而，最近在沙漠中发现了一些行星，这出乎人们的意料，也突显了我们在理解上的差距。这些炽热的海王星的起源尚不清楚，它们为研究行星形成的极端结果提供了一个独特的机会。这些正常过程的离群值使我们能够作为行星形成理论的基准，许多典型的简并现象被剔除。有了这个提议，我们将结合来自TESS、NGTS、Coralie、HARPS和Gaia的光度和光谱观测，开展一个雄心勃勃的全面研究计划，调查沙漠中行星的性质和起源。(1)我们将揭示沙漠中行星的无偏人口统计属性，找出行星质量、半径、密度、内部结构和主恒星属性的分布。(2)我们将通过确定外部伴星的存在和恒星的局部密度来建立这些系统的动力学背景。(3)我们将把测量的人口统计、动力学和内部结构与更广泛的形成和演化理论联系起来。这些综合结果不仅将改变我们对沙漠中行星的理解，还将改变我们对行星系统更广泛的形成、结构和演化的理解。

Our knowledge of exoplanets has undergone a step change since the discovery of 51 Peg b 25 years ago. Planets are now commonplace, with most stars found to be hosting planetary systems. In the set of over 4300 planets known, trends and gaps in the distribution are seen with respect to planet size, composition and host star properties, arising from the formation and evolution processes which sculpt these worlds.A striking signature in the planet distribution is the 'Neptunian desert', a dearth of Neptune-like planets orbiting close to their host stars. Planets which arrive so close to their stars are evaporated away, or are disrupted entirely by the strong gravitational forces of the star. Yet, recently a number of planets have been discovered inside the desert, surprising expectations and highlighting a gap in our understanding. The origin of these hot Neptunes is unknown, and they present a unique opportunity to study the extreme outcomes of planet formation. Such outliers of the normal processes allow us to benchmark planetary formation theories, with many of the typical degeneracies stripped away.With this proposal, we will combine photometric and spectroscopic observations from TESS, NGTS, CORALIE, HARPS and Gaia to carry out an ambitious and comprehensive research program investigating the nature and origins of planets in the desert. (1) We will uncover the unbiased demographic properties of the in-desert planets, finding the distributions of planet mass, radius, density, internal structure and host star properties. (2) We will establish the dynamical context of these systems by determining the presence of outer companions and local density of stars (3) We will connect the measured demographics, dynamics and internal structure to wider formation and evolution theory. The combined results will transform our understanding not only of the in-desert planets but of the wider formation, structure and evolution of planetary systems.