A Metallicity Recipe for Rocky Planets
A Metallicity Recipe for Rocky Planets
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岩石行星的金属丰度配方
DOI：
10.1093/mnras/stv1639
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发表时间：
2015
影响因子：
4.8
通讯作者：
Eve J. Lee
中科院分区：
文献类型：
--
作者：
R. Dawson;E. Chiang;Eve J. Lee
大小介于地球和海王星之间的行星分为两类：纯粹的岩石天体，其大气层对其大小的贡献可以忽略不计；以及较大的气体包裹行星，拥有大量且光学厚的大气层。我们表明，行星是否形成岩石或气体包裹取决于其母盘的固体表面密度。岩石核心的组装时间对圆盘固体表面密度很敏感。较低的表面密度会产生较小的行星胚胎；为了组装一个给定质量的核心，较小的胚胎需要在相距较远的物体之间进行更多的合并，因此形成时间呈指数增长。气体吸积模拟得出一条经验法则，即岩石核心必须至少为 2$M_\oplus$ 才能从其母星云获得具有体积意义的大气层。在低固体表面密度的盘中，这种质量的核心只有在气体盘消散后才会出现，因此仍然是纯粹的岩石。表面密度越高的盘，在气盘的寿命内，能更快地形成巨大的核心，从而产生气体包裹的行星。我们根据观测结果测试模型预测，使用行星半径作为气体-岩石含量的观测代理，并使用主星金属丰度作为盘固体表面密度的代理。理论可以解释富含金属的恒星拥有主要由气体包裹的行星的观察结果。
Planets with sizes between those of Earth and Neptune divide into two populations: purely rocky bodies whose atmospheres contribute negligibly to their sizes, and larger gas-enveloped planets possessing voluminous and optically thick atmospheres. We show that whether a planet forms rocky or gas-enveloped depends on the solid surface density of its parent disk. Assembly times for rocky cores are sensitive to disk solid surface density. Lower surface densities spawn smaller planetary embryos; to assemble a core of given mass, smaller embryos require more mergers between bodies farther apart and therefore exponentially longer formation times. Gas accretion simulations yield a rule of thumb that a rocky core must be at least 2$M_\oplus$ before it can acquire a volumetrically significant atmosphere from its parent nebula. In disks of low solid surface density, cores of such mass appear only after the gas disk has dissipated, and so remain purely rocky. Higher surface density disks breed massive cores more quickly, within the gas disk lifetime, and so produce gas-enveloped planets. We test model predictions against observations, using planet radius as an observational proxy for gas-to-rock content and host star metallicity as a proxy for disk solid surface density. Theory can explain the observation that metal-rich stars host predominantly gas-enveloped planets.
DOI：
10.1146/annurev-astro-081811-125523
发表时间：
2012-03
影响因子：
33.3
作者：
W. Kley;R. Nelson
通讯作者：
W. Kley;R. Nelson