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所谓的内部行星紧密堆积的系统中。这些行星的质量等于或略大于地球的质量，并且围绕其恒星的轨道是有序的。这些行星可能是在它们现在的位置或附近形成的。研究人员提出了一种名为“由内而外的行星形成”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一个环。当这些物质第一次形成行星时，行星扫出剩余的鹅卵石，在围绕星星的轨道上形成一个空的空间。然后，一个新的卵石环在行星外形成。这个过程不断重复，在母星星周围形成一个行星系统。研究人员将研究在这个理论下形成行星的物质供应的三个方面：他们将寻找中断圆盘中鹅卵石和尘埃流动的力量;他们将研究这些早期行星的氢气和氦气;最后他们将考虑磁场对这个过程的影响。该项目通过提高我们对太阳系等行星系统如何形成和演变的理解来服务于国家利益。研究人员将把这一研究课题纳入他们的教学活动，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。这些行星的质量从地球到超级地球不等，轨道排列良好。这些特性表明它们是在目前的位置附近形成的。“由内而外的行星形成”理论阐述了科学、技术和革新政策的性质。它涉及到行星从原行星盘内部区域富含“卵石”的环中顺序形成。由粉尘凝结形成的卵石由于气体阻力而迁移到内部圆盘，并在局部压力最大时聚集。一旦第一颗行星从卵石环中形成，它就会长大并打开一个缺口。一个新的卵石环开始在行星外部形成，这个过程重复着。STIP行星的密度范围很广，这意味着一些行星被H/He大气层包围，其质量高达行星质量的10%。然而，它们并没有遭受失控的H/He吸积而成为气体巨星。这项研究将调查三个方面的供应链的材料和从科学、技术和创新方案的行星在其形成和随后的演变。首先，研究人员将研究卵石通过盘平面的径向向内漂移，重点是流动不稳定性，这种不稳定性可能通过形成大量的微行星来破坏卵石漂移。其次，他们将研究氢/氦气体吸积到地球以下到超级地球质量的类地行星。第三，他们将计算磁调节的STIPs大气蒸发率。研究者将把这个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.