Collaborative Research: Pebbles and Gas - The Supply Chain for Compact Planetary Systems

宇宙中已知的最常见的行星类型发生在被称为紧凑内行星的系统中。这些行星的质量等于或略大于地球的质量，它们围绕恒星的轨道排列有序。这些行星很可能是在其当前位置或其附近形成的。研究人员提出了一种名为Inside-Out行星形成的理论，该理论认为，碎片盘内部区域的高压迫使鹅卵石、气体和尘埃聚集在一起形成环状。当这些物质第一次形成行星时，行星扫出残留的鹅卵石，在其恒星周围的轨道上形成一个空白空间。然后，在行星外形成了一个新的鹅卵石环。这个过程会重复，在母星周围形成一个行星系统。根据这一理论，研究人员将研究构成行星的物质供应的三个方面：他们将寻找阻止圆盘中鹅卵石和尘埃流动的力；他们将研究这些早期行星中添加的氢气和氦气体；最后，他们将考虑磁效应对这一过程的影响。这个项目服务于国家利益，通过提高我们对太阳系等行星系统如何形成和演化的理解。研究人员将把这一研究课题纳入他们的教学活动中，并培养一名研究生和博士后研究人员。具有紧密堆积的内行星(STIPS)的系统可能拥有宇宙中最常见的行星类型。这些行星的质量范围从地球到超级地球，并且轨道排列良好。这些属性支持在其当前位置附近形成。“由内而外的行星形成”理论解决了STIPS的性质。它涉及到由原行星盘内部富含卵石的环依次形成行星的过程。由尘埃凝结形成的鹅卵石，由于气体的拖曳而迁移到内盘，并在局部最大压力下聚集。一旦第一颗行星从鹅卵石环中形成，它就会长大，从而打开一个缺口。一个新的鹅卵石环开始在行星外部形成，这个过程重复。STIP行星的密度范围很大，这意味着一些行星被高达地球质量10%的H/He大气所包围。然而，它们并没有遭受H/He的失控吸积而成为气态巨星。这项研究将调查STIP行星形成和随后演变过程中来往于行星的材料供应链的三个方面。首先，研究人员将研究鹅卵石通过圆盘平面的径向向内漂移，重点是流动不稳定性，这种不稳定性可能会通过形成大质量的行星体来扰乱鹅卵石漂移。第二，他们将研究氢/氦气体在亚地至超地球质量的类地行星上的吸积。第三，他们将计算STIPS的磁控大气蒸发率。研究人员将把这一研究课题纳入教学活动，并培养一名研究生和博士后研究员。

The most common type of planet known in the universe occurs in what are known as Systems with Tightly-Packed Inner Planets. These planets have masses equal to or somewhat larger than the Earth's mass, and orbits around their stars that are well ordered. The planets likely formed in or near their present locations. The investigators have proposed a theory called Inside-Out Planet Formation that suggests that high pressure in the inner regions of debris disks forces pebbles, gas, and dust to group together in a ring. When these materials first form a planet, the planet sweeps out leftover pebbles to make an empty space in its orbit around its star. Then, a new ring of pebbles forms outside the planet. This process repeats, creating a system of planets around the parent star. The investigators will study three aspects of the supply of material that forms the planets under this theory: they will look for forces that would interrupt the flow of pebbles and dust in the disk; they will study hydrogen and helium gas addition to these early planets; and finally they will consider magnetic effects on this process. This project serves the national interest by improving our understanding of how planetary systems like our Solar System formed and evolved. The investigators will include this research topic in their teaching activities, and train a graduate student and post-doctoral researcher.Systems with Tightly-packed Inner Planets (STIPs) could host the most common type of planets in the universe. These planets have masses ranging from Earth to super-Earth, and well-aligned orbits. These properties argue for formation near their present locations. The "Inside-Out Planet Formation" theory addresses the properties of STIPs. It involves the sequential formation of planets from "pebble"-rich rings in inner regions of protoplanetary disks. Pebbles, formed from dust coagulation, migrate to the inner disk due to gas drag and collect at a local pressure maximum. Once the first planet forms from the pebble ring, it grows to open a gap. A new pebble ring starts to form exterior to the planet, and the process repeats. The STIP planets have a wide range of densities, implying some are surrounded by H/He atmospheres with up to ~10% of the planet's mass. However, they did not suffer runaway accretion of H/He to become gas giants. This research will investigate three aspects of the supply chain of material to and from the STIP's planets during both their formation and subsequent evolution. First, the investigators will study the radial inward drift of pebbles through the disk plane, focusing on streaming instabilities that could disrupt pebble drift by forming massive planetesimals. Second, they will study H/He gas accretion to terrestrial planets of sub-Earth to super-Earth masses. Third, they will calculate magnetically-regulated atmospheric evaporation rates of STIPs. The investigators will include this research topic in their teaching activities, and train a graduate student and post-doctoral researcher.