论文标题
系外行星和棕色矮人的矿物雪花：微孔隙度，尺寸分布和粒子形状的影响
Mineral snowflakes on exoplanets and brown dwarfs: Effects of micro-porosity, size distributions, and particle shape
论文作者
论文摘要
系外行星大气表征已成为理解系外行星形成，进化的重要工具。但是，云仍然是表征的关键挑战：即将到来的太空望远镜（例如JWST，Ariel）和基于地面的高分辨率光谱仪（例如Crires+）将产生数据，需要详细了解云形成和云效应。我们旨在了解云颗粒的微孔度如何影响云结构，粒径和材料组成。我们检查了微孔颗粒，粒度分布和非球形云颗粒的光谱效应。我们扩展了动力学的非平衡云形成模型，并使用了规定的1D（T_GAS-P_GAS）漂移 - 段落轮廓的网格。我们应用了有效的培养基理论和MIE理论，以微孔隙度和衍生的粒径分布对云颗粒的光谱特性进行建模。我们使用了空心球的统计分布来表示非球形云颗粒的影响。高度微孔云颗粒（90％真空）具有更大的表面积，使大气中的有效体积生长高于紧凑型颗粒。这些矿物雪花的单散射反照率和横截面区域的增加导致云甲板仅在〜100 $ {\ rmμm} $的波长下变细，而不是在〜20 $ {\ rmμm}的〜20 $ {\ rmμm}中，对于紧凑型云颗粒。当云颗粒发生随着局部变化的高斯尺寸分布而出现时，还可以看到反照率的显着增强。非球形颗粒增加了硅酸盐光谱特征的不透明度，这进一步增加了云在光学上变薄的波长。 JWST Miri将基于云在光学上薄的波长，对微孔和非球形云颗粒的特征敏感。
Exoplanet atmosphere characterisation has become an important tool in understanding exoplanet formation, evolution. However, clouds remain a key challenge for characterisation: upcoming space telescopes (e.g. JWST, ARIEL) and ground-based high-resolution spectrographs (e.g. CRIRES+) will produce data requiring detailed understanding of cloud formation and cloud effects. We aim to understand how the micro-porosity of cloud particles affects the cloud structure, particle size, and material composition. We examine the spectroscopic effects of micro-porous particles, the particle size distribution, and non-spherical cloud particles. We expanded our kinetic non-equilibrium cloud formation model and use a grid of prescribed 1D (T_gas-p_gas) DRIFT-PHOENIX profiles. We applied the effective medium theory and the Mie theory to model the spectroscopic properties of cloud particles with micro-porosity and a derived particle size distribution. We used a statistical distribution of hollow spheres to represent the effects of non-spherical cloud particles. Highly micro-porous cloud particles (90% vacuum) have a larger surface area, enabling efficient bulk growth higher in the atmosphere than for compact particles. Increases in single-scattering albedo and cross-sectional area for these mineral snowflakes cause the cloud deck to become optically thin only at a wavelength of ~100 ${\rm μm}$ instead of at the ~20 ${\rm μm}$ for compact cloud particles. A significant enhancement in albedo is also seen when cloud particles occur with a locally changing Gaussian size distribution. Non-spherical particles increase the opacity of silicate spectral features, which further increases the wavelength at which the clouds become optically thin. JWST MIRI will be sensitive to signatures of micro-porous and non-spherical cloud particles based on the wavelength at which clouds are optically thin.
