From disks to planets: end-to-end modelling of the planet formation process

长期以来，人类一直在研究行星系统是如何形成和演化的。这个问题的答案对于把我们置于宇宙的背景中，对于寻找其他可居住的世界，最终对于寻找其他生命来说是至关重要的。尽管在过去的十年里，在其他恒星周围发现了250多颗行星，但我们对它们和我们的太阳系是如何形成的了解仍然非常不完整。使用由首席研究员开发的新型混合计算机代码，首次有可能对整个形成过程进行端到端模拟——本质上，是关于年轻恒星周围的圆盘如何将自己转化为行星。这段代码结合了为行星系统优化的“n体”方案的速度（基于现有的SyMBA包）和原恒星盘的一维实现（它表示由嵌套环组成的盘）。这两个部分是用标准公式结合起来的：(i)行星与圆盘的动力学相互作用，（ii）行星通过引力从圆盘中吸入气体来增加其大气的速率。以计算机代码为主要工具，这里提出的研究旨在提高我们对行星形成的理解。随着时间的推移，将对代码进行一系列关键的补充和增强，每一个都允许研究行星形成过程的一个新方面。与此同时，代码的高速度——几天的时间来模拟一个原恒星气体盘几百万年的寿命——将被保持。计划培养3名暑期学生、3名研究生和1名博士后。在资助期结束时，完成的、完整的文档和严格测试的代码将免费提供给公众。

Human beings have long been occupied with the question of how planetary systems form and evolve. The answer is central to placing ourselves in context within the Universe, to the search for other habitable worlds, and ultimately, to the search for other life. Though more than 250 planets have been detected around other stars over the past decade, our knowledge of how both they and our own Solar System came to be is still very incomplete. Using a new hybrid computer code developed by the principal investigator, it is for the first time possible to perform an end-to-end simulation of the entire formation process---in essence, of how a disk around a young star converts itself into planets. This code combines the speed of an ``N-body" scheme optimized for planetary systems (based on the existing SyMBA package) with a one-dimensional implementation of a protostellar disk (which represents the disk as made up of nested rings). These two parts are coupled using standard prescriptions for (i) the dynamical interaction of a planet with a disk, and (ii) the rate at which a planet grows its atmosphere by gravitationally pulling in gas from the disk. With this computer code as the primary tool, the research proposed here is aimed at advancing our understanding of planet formation. A series of key additions and enhancements will be made to the code over time, each allowing a new aspect of the planet formation process to be studied. At the same time, the high speed of the code---several days to simulate the several-million-year lifespan of a protostellar gas disk---will be maintained. It is intended that three summer students, three graduate students and one postdoctoral researcher will be trained/employed over the course of the project. At the end of the funding period, the finished, fully documented and rigorously tested code will be made freely available to the public.