Light Scattering Measurements of KCl Particles as an Exoplanet Cloud Analog

IF 3.8 Q2 ASTRONOMY & ASTROPHYSICS The Planetary Science Journal Pub Date : 2024-08-27 DOI:10.3847/psj/ad6569
Colin D. Hamill, Alexandria V. Johnson, Peter Gao
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Abstract

Salt clouds are predicted to be common on warm exoplanets, but their optical properties are uncertain. The Exoplanet Cloud Ensemble Scattering System (ExCESS), a new apparatus to measure the scattering intensity and degree of linear polarization for an ensemble of particles, is introduced here and used to study the light scattering properties of KCl cloud analogs. ExCESS illuminates particles with a polarized laser beam (532 nm) and uses a photomultiplier tube detector to sweep the plane of illumination. Scattering measurements for KCl particles were collected for three size distributions representative of modeled clouds for the warm exoplanet GJ 1214b. Our measurements show that Lorenz–Mie calculations, commonly used to estimate the light scattering properties of assumedly spherical cloud particles, offer an inaccurate depiction of cubic and cuboid KCl particles. All of our measurements indicate that Lorenz–Mie scattering overestimates the backscattering intensity of our cloud analogs and incorrectly predicts the scattering at mid-phase angles (∼90°) and the preferential polarization state of KCl scattered light. Our results align with the general scattering properties of nonspherical particles and underscore the importance of further understanding the effects that such particles will have on radiative transfer models of exoplanet atmospheres and reflected light observations of exoplanets by the upcoming Nancy Grace Roman Space Telescope and Habitable Worlds Observatory.
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作为系外行星云模拟物的 KCl 粒子的光散射测量
据预测,盐云在温暖的系外行星上很常见,但其光学特性还不确定。这里介绍的系外行星云集合散射系统(ExCESS)是一种测量粒子集合的散射强度和线性极化程度的新仪器,用于研究氯化钾云类似物的光散射特性。ExCESS 使用偏振激光束(532 nm)照射粒子,并使用光电倍增管探测器扫描照射平面。对 KCl 粒子的散射测量是针对暖系外行星 GJ 1214b 的模型云的三种代表性尺寸分布收集的。我们的测量结果表明,通常用于估计假定为球形的云粒子的光散射特性的洛伦兹-米计算,对立方体和长方体氯化钾粒子的描述并不准确。我们的所有测量结果都表明,洛伦兹-米散射高估了我们的云模拟物的反向散射强度,并且错误地预测了中相角(∼90°)的散射和氯化钾散射光的优先偏振态。我们的结果与非球形粒子的一般散射特性相吻合,并强调了进一步了解这类粒子对系外行星大气辐射传递模型以及即将到来的南希-格蕾丝-罗曼太空望远镜和宜居世界天文台对系外行星反射光观测的影响的重要性。
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来源期刊
The Planetary Science Journal
The Planetary Science Journal Earth and Planetary Sciences-Geophysics
CiteScore
5.20
自引率
0.00%
发文量
249
审稿时长
15 weeks
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