用Rosetta/VIRTIS对~（67）P/ CG核的表面组成进行了研究。I）着陆前飞行阶段
The global surface composition of 67P/CG nucleus by Rosetta/VIRTIS. I) Prelanding mission phase
摘要：
从2014年8月至11月，罗塞塔轨道飞行器进行了广泛的观测活动，旨在表征67 P/CG核的性质，并选择菲莱着陆点。这项活动导致了67 P/CG核被照亮部分的全球地图的制作。在这段着陆前的阶段，彗星的日心距离从3.62天文单位减少到2.93天文单位，而罗塞塔则在100到10公里的距离上绕着彗星核运行。VIRTIS-M，即轨道器上的可见光和红外热成像光谱仪-制图通道（Coradini等人，2007年），已经获得了整个受照表面的0.25-5.1微米高光谱数据，例如北半球和赤道地区，空间分辨率在2.5米/像素和25米/像素之间。I/F光谱已被校正为在3.5-5.1微米范围内的热发射去除和表面的光度响应。由此产生的反射光谱已被用于计算几个彗星光谱指标（CSI）：在0.55微米、0.5-0.8微米和1.0-2.5微米光谱斜率、3.2微米有机物质和2.0微米水冰带参数下的单次散射（中心，深度），目的是绘制它们在表面上的空间分布图，并研究它们在核心向太阳移动时的时间变化。实际上，在整个研究期间，核表面显示出单次散射的显著增加，以及0.5-0.8和1.0-2.5微米光谱斜率的减小，表明反射率的平坦化。我们把这种效应的起源归因于部分去除的尘埃层所造成的增加贡献的水升华的气体活动彗星越过冻结线。
英文摘要：
From August to November 2014 the Rosetta orbiter has performed an extensive observation campaign aimed at the characterization of 67P/CG nucleus properties and to the selection of the Philae landing site. The campaign led to the production of a global map of the illuminated portion of 67P/CG nucleus. During this prelanding phase the comet's heliocentric distance decreased from 3.62 to 2.93 AU while Rosetta was orbiting around the nucleus at distances between 100 to 10 km. VIRTIS-M, the Visible and InfraRed Thermal Imaging Spectrometer - Mapping channel (Coradini et al. 2007) onboard the orbiter, has acquired 0.25-5.1 micron hyperspectral data of the entire illuminated surface, e.g. the north hemisphere and the equatorial regions, with spatial resolution between 2.5 and 25 m/pixel. I/F spectra have been corrected for thermal emission removal in the 3.5-5.1 micron range and for surface's photometric response. The resulting reflectance spectra have been used to compute several Cometary Spectral Indicators (CSI): single scattering albedo at 0.55 micron, 0.5-0.8 micron and 1.0-2.5 micron spectral slopes, 3.2 micron organic material and 2.0 micron water ice band parameters (center, depth) with the aim to map their spatial distribution on the surface and to study their temporal variability as the nucleus moved towards the Sun. Indeed, throughout the investigated period, the nucleus surface shows a significant increase of the single scattering albedo along with a decrease of the 0.5-0.8 and 1.0-2.5 micron spectral slopes, indicating a flattening of the reflectance. We attribute the origin of this effect to the partial removal of the dust layer caused by the increased contribution of water sublimation to the gaseous activity as comet crossed the frost-line.
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