Experimental Studies of Pebble Accretion in the Protoplanetary Disk

围绕我们的太阳和其他恒星的行星的形成始于尘埃大小的粒子粘在一起，逐渐形成越来越大的物体。从鹅卵石大小的物体到千米大小的物体的成长阶段可能遵循几种不同路线中的一种或多种，这取决于物体与恒星的距离和恒星的年龄。该项目将通过实验研究鹅卵石大小的尘埃、冰和岩石团块之间的大范围碰撞，以确定导致更大物体生长的条件。这些实验的结果将有助于解决有关行星形成关键阶段的基本问题，包括水冰和其他生物学上重要的分子在粘着过程中所起的作用。许多实验将在微重力或自由落体环境中进行，以复制早期太阳系的条件。碰撞的视频数据将被分析，以了解在行星形成的早期阶段类似碰撞的结果。本科生和研究生将参与实验，视频数据将通过公共网站共享，使公众、学生和研究人员能够直观地了解行星系统历史上的这一关键阶段。提议的活动是对原行星盘中低能碰撞的实验性探索，以更好地理解鹅卵石大小（厘米尺度）的聚集体和固体的碰撞演化，行星的最初组成部分。这些实验将在参数空间上扩展现有的数据库，包括与硅酸盐混合的冰粒子，以研究外太阳系（水蒸气凝结的霜冻线以外）的吸积效率，以及研究在适度撞击速度下大型聚集体之间的碰撞，无论聚集体中是否有冰粒子。这些鹅卵石可能通过成对的碰撞吸积或参与局部引力不稳定来形成更大的公里尺度的星子。根据原行星状星云的局部条件，这些过程可能同时发生。在吸积增长模型中，不确定性的一个主要来源是小物体和尘埃聚集体以预期的低速（~0.1 - 10m /s）碰撞的行为。拟议中的实验将为这些模型增加急需的数据，以帮助确定吸积增长产生星子的条件，以及各种星云环境中鹅卵石之间碰撞的结果。这项工作将涉及一个由几名本科生和一名研究生组成的团队，负责实验的设计、操作和解释，以及结果的发表。实验数据由高速视频组成，将通过公共网站microgravity.physics.ucf.edu与K-12教育工作者和更广泛的研究界共享。

The formation of planets around our own Sun and around other stars begins with dust-sized particles sticking together and gradually forming larger and larger objects. The stage of growth from pebble-sized objects to km-scale objects may follow one or more of several different routes, depending on the distance of the objects from the star and the age of the star. This project will experimentally study a broad range of collisions between pebble-sized clumps of dust, ice and rock to determine the conditions that lead to growth of larger objects. The results of these experiments will help resolve fundamental questions about a critical stage in planet formation, including the role that water ice and other biologically important molecules play in the sticking process. Many of the experiments will take place in a microgravity or free-fall environment in order to replicate the conditions in the early solar system. Video data of the collisions will be analyzed to understand the outcomes of similar collisions in the early stages of planet formation. Undergraduate and graduate students will participate in the experiments, and the video data will be shared through public websites, allowing the general public, students, and researchers to visualize this critical stage in the history of planetary systems.The proposed activity is an experimental exploration of low-energy collisions in the protoplanetary disk to better understand the collisional evolution of pebble-sized (cm-scale) aggregates and solids, the initial building blocks of planets. The experiments will extend the current database in parameter space by including icy particulates mixed in with silicates to study the accretion efficiency in the outer solar system (beyond the frost line where water vapor condensed) and by studying collisions between large-scale aggregates at modest impact speed both with and without ice particles in the aggregates. These pebbles may grow through pairwise collisional accretion or participate in local gravitational instabilities to form larger km-scale planetesimals. It is possible that some combination of these processes took place, depending on the local conditions in the protoplanetary nebula. A major source of uncertainty in the accretional growth model is the behavior of small objects and aggregates of dust colliding at the low speeds expected (~0.1 - 10 m/s). The proposed experiments would add much-needed data to these models to help determine the conditions under which accretional growth can produce planetesimals and the outcomes of collisions between pebbles in various nebular environments. The proposed work will involve a team of several undergraduate students and one graduate student in the design, operation, and interpretation of the experiments as well as publication of results. The experimental data consist of high speed videos that will be shared with K-12 educators and the broader research community through the public website microgravity.physics.ucf.edu.