The New Horizons spacecraft observed Pluto and Charon at solar-phase angles between 16 and 169. In this work, we use the Multispectral Visible Imaging Camera (MVIC) observations to construct multiwavelength phase curves of Pluto’s atmosphere, using the limb scatter technique. Observational artifacts and biases were removed using Charon as a representative airless body. The size and distribution of the haze particles were constrained using a Titan fractal aggregate phase function. We find that monodispersed and log-normal populations cannot simultaneously describe the observed steep forward scattering, indicative of wavelength-scale particles, and the non-negligible backscattering indicative of particles much smaller than the wavelength. Instead, we find it necessary to use bimodal or power-law distributions, especially below ∼200 km, to properly describe the MVIC observations. Above 200 km, where the atmosphere is isotropically scattering, a monodisperse, log-normal, or a bimodal/power law approximating a monodispersed population is able to fit the phase curves well. As compared to the results of previously published articles, we find that Pluto’s atmosphere must contain haze particle number densities an order of magnitude greater for small (∼10 nm) and large (∼1 μm) radii, and relatively fewer intermediate sizes (∼100 nm). These conclusions support a lower aggregate aerosol growth rate than that found by Gao et al., indicating a higher charge-to-radius ratio, upwards of 60e ⁻ μm⁻¹. In order to generate large particles with a lower growth rate, the atmosphere must also have a lower sedimentation velocity (<∼0.01 m s⁻¹ at 200 km), which is possible with a fractal dimension of less than 2.

新视野号航天器以 16 到 169 度的太阳相位角观测冥王星和卡戎。在这项工作中，我们使用多光谱可见光成像相机 (MVIC) 观测，利用临边散射技术构建冥王星大气的多波长相位曲线。使用 Charon 作为代表性的无气体去除了观测伪像和偏差。雾霾颗粒的大小和分布使用 Titan 分形聚集相函数进行约束。我们发现，单分散和对数正态分布不能同时描述观察到的陡峭前向散射（指示波长尺度粒子）和不可忽略的反向散射（指示远小于波长的粒子）。相反，我们发现有必要使用双峰或幂律分布，尤其是在 200 公里以下，正确描述 MVIC 观察结果。在 200 公里以上，大气呈各向同性散射，近似单分散群体的单分散、对数正态或双峰/幂律能够很好地拟合相位曲线。与之前发表的文章的结果相比，我们发现冥王星的大气层必须包含雾粒子数密度，对于小（~10 nm）和大（~1μ m）半径，以及相对较少的中间尺寸（~100 nm）。这些结论支持比 Gao 等人发现的更低的总气溶胶增长率，表明更高的电荷半径比，高达 60 e ^- μ m ^-1。为了产生具有较低生长速率的大颗粒，大气还必须具有较低的沉降速度（<∼0.01 ms ^-1 at 200 km），这在分形维数小于 2 的情况下是可能的。