Muñoz Antonio García, Isaak Kate G
Scientific Support Office, Directorate of Science and Robotic Exploration, European Space Agency/European Space Research and Technology Centre (ESA/ESTEC), 2201 AZ Noordwijk, The Netherlands
Scientific Support Office, Directorate of Science and Robotic Exploration, European Space Agency/European Space Research and Technology Centre (ESA/ESTEC), 2201 AZ Noordwijk, The Netherlands.
Proc Natl Acad Sci U S A. 2015 Nov 3;112(44):13461-6. doi: 10.1073/pnas.1509135112. Epub 2015 Oct 21.
Kepler-7b is to date the only exoplanet for which clouds have been inferred from the optical phase curve--from visible-wavelength whole-disk brightness measurements as a function of orbital phase. Added to this, the fact that the phase curve appears dominated by reflected starlight makes this close-in giant planet a unique study case. Here we investigate the information on coverage and optical properties of the planet clouds contained in the measured phase curve. We generate cloud maps of Kepler-7b and use a multiple-scattering approach to create synthetic phase curves, thus connecting postulated clouds with measurements. We show that optical phase curves can help constrain the composition and size of the cloud particles. Indeed, model fitting for Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate anisotropic efficiency, conclusions consistent with condensates of silicates, perovskite, and silica of submicron radii. We also show that we are limited in our ability to pin down the extent and location of the clouds. These considerations are relevant to the interpretation of optical phase curves with general circulation models. Finally, we estimate that the spherical albedo of Kepler-7b over the Kepler passband is in the range 0.4-0.5.
开普勒-7b是迄今为止唯一一颗已从光学相位曲线推断出存在云层的系外行星，该曲线是通过对整个行星盘进行可见波长的亮度测量，并将其作为轨道相位的函数得到的。此外，相位曲线似乎主要由恒星反射光主导，这使得这颗近距离的气态巨行星成为一个独特的研究案例。在这里，我们研究了测量得到的相位曲线中所包含的有关行星云层覆盖范围和光学特性的信息。我们生成了开普勒-7b的云层图，并使用多重散射方法创建合成相位曲线，从而将假定的云层与测量结果联系起来。我们表明，光学相位曲线有助于限制云层颗粒的组成和大小。实际上，对开普勒-7b进行模型拟合需要吸收性较差的颗粒，这些颗粒以低至中等的各向异性效率进行散射，这一结论与亚微米半径的硅酸盐、钙钛矿和二氧化硅的冷凝物一致。我们还表明，我们在确定云层范围和位置的能力上存在局限性。这些考虑因素对于用一般环流模型解释光学相位曲线具有重要意义。最后，我们估计开普勒-7b在开普勒波段的球面反照率在0.4至0.5之间。
