Heavy-Metal Jupiters by Major Mergers

加州大学伯克利分校的一个研究小组试图了解富含金属的木星的起源，他们特别询问，它们是否可能来自较小的原行星之间的碰撞。一些质量相当于木星的太阳系外行星含有多达100个地球质量的“金属”，即氢和氦以外的元素。传统的气态巨星形成理论认为，以气体为主的行星起源于氢和氦，它们聚集在一个只有10块地球岩石和冰的固体核心上，从而产生了这样的“重金属”木星。这项提议提出的问题是，巨大岩石核心之间的碰撞是否会产生富含金属的巨星。在行星形成时代，成对的核心可以相继碰撞和合并，每次合并都会使合并产品的金属含量翻一番。这种碰撞增长的“巨型撞击”阶段一直被认为适用于地球这样的岩石行星；这个项目试图将这个模型扩展到像木星这样的气体巨星。该项目将模拟形成行星核心的合并历史以及它们通过盘状气体的增长，以重现观测到的气体巨星的金属含量。这项工作将为我们太阳系的木星可能是如何被碰撞塑造的提供背景。这项工作将培养一名进入科学大军的研究生，并培养有志于教授物理科学的本科生研究助理。调查人员将与当地的K-12项目和高中物理教师合作，对学生和教师进行建模和研究方面的教育。同时合并和来自圆盘的气体吸积将用开源的N-Body代码反弹建模，配备了气体吸积和圆盘扭矩的例程。一个模拟原行星内部的“子网格”代码将为反弹的碰撞算法提供半径。将探索行星气体吸积、撞击产生的大气质量损失和碰撞合并的不同处方-完美与肇事逃逸，将用快速机器学习算法建模。其目的是调查合并+气体吸积模拟的可能结果的范围，并再现巨行星经验质量-金属丰度关系中的平均趋势和显著的大分散。这项工作还将在不同程度上与其他外巨型可观测天体联系起来，包括半长轴、偏心率、多重性、发光和自旋。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A team from the University of California-Berkeley seek to understand the origin of metal-rich Jupiters, asking specifically whether they can arise from collisions between smaller protoplanets. Some Jupiter-mass extrasolar planets contain as much as 100 Earth masses of 'metals', i.e. elements other than hydrogen and helium. Such 'heavy-metal' Jupiters are not expected from the conventional theory of gas giant formation, which predicts that a gas-dominated planet originates from hydrogen and helium accreting onto a solid core having only 10 Earth masses of rock and ice. This proposal asks whether metal-rich giants can arise from collisions between massive rocky cores. During the planet formation era, pairs of cores can successively collide and merge, with each merger doubling the metal content of the merger product. Such a 'giant impacts' phase of collisional growth has long been put forward to hold for rocky planets like the Earth; this project seeks to extend this model to gas giants like Jupiter. The project will simulate the merger history of forming planet cores as well as their growth through disk gas to reproduce the observed metal contents of gas giants. The work will provide context for how our Solar System’s Jupiter may have been shaped by collisions. The work will train a graduate student to join the scientific workforce, and train undergraduate research assistants with ambitions to teach the physical sciences. The investigators will partner with local K-12 programs and high school physics teachers to educate students and teachers in modeling and research. Concurrent mergers and gas accretion from the disk will be modeled with the open-source N-body code REBOUND, outfitted with routines for gas accretion and disk torques. A 'sub-grid' code that models protoplanet interiors will provide radii for use in REBOUND’s collision algorithm. Different prescriptions for planetary gas accretion, impact-generated atmospheric mass loss, and collisional mergers — perfect vs. hit-and-run, to be modeled with fast machine-learning algorithms — will be explored. The goal is to survey the range of possible outcomes in merger + gas accretion simulations, and to reproduce the mean trend and remarkably large scatter in the empirical mass-metallicity relation for giant planets. The work will also connect to varying extents with other exo-giant observables, including semi-major axes, eccentricities, multiplicities, luminosities, and spins.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.