罗塞塔号上OSIRIS和VIRTIS-M观测到的返回春分点67 P/Churyumov-Gerasimenko彗星尘埃和气体产生的日变化
Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta
摘要：
2015年4月27日，当67 P/C-G距离太阳1.76天文单位并向近日点移动时，罗塞塔号上的OSIRIS和VIRTIS-M仪器观测到彗星在一次完整的旋转过程中不断演变的尘埃和气体彗发。我们的目的是表征尘埃，H2O和CO2气体的空间分布在内部彗发。要做到这一点，我们进行了定量分析的灰尘和气体的释放，并比较观察到的H2O生产率与使用热物理模型计算的。在这项研究中，我们选择了OSIRIS WAC图像在612 nm（灰尘）和VIRTIS-M图像立方体在612 nm，2700 nm（H2O）和4200 nm（CO2）。我们测量的平均信号在一个圆环，研究彗星周围的空间变化，并在一个部门的环，研究时间变化在向阳方向与彗星旋转，都在一个固定的距离为3.1公里的彗星中心。尘埃和水之间的空间相关性都来自彗星的阳光照射面，表明水是这段时间尘埃活动的主要驱动力。CO2的空间分布与水、尘的相关性不明显。彗星自转时，尘埃亮度和水的产生率之间没有很强的时间相关性。尘埃亮度在太阳下经度0度处显示出峰值，这在水的产生中并不明显。在同一时期，二氧化碳的产生也有一个最大值。过量的测量水的生产，相对于使用一个简单的热物理模型计算的值，观察时，头叶和南半球的地区具有强烈的季节性变化被照亮。当水产量（测量和模型）显示最大值时，粉尘产量急剧减少，发生在典型的北方巩固地区被照亮，而南半球季节变化强烈的地区则处于阴影中。
英文摘要：
On 27 Apr 2015, when 67P/C-G was at 1.76 au from the Sun and moving towards perihelion, the OSIRIS and VIRTIS-M instruments on Rosetta observed the evolving dust and gas coma during a complete rotation of the comet. We aim to characterize the dust, H2O and CO2 gas spatial distribution in the inner coma. To do this we performed a quantitative analysis of the release of dust and gas and compared the observed H2O production rate with the one calculated using a thermo-physical model. For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H2O) and 4200 nm (CO2). We measured the average signal in a circular annulus, to study spatial variation around the comet, and in a sector of the annulus, to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet centre. The spatial correlation between dust and water, both coming from the sun-lit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO2 is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0deg sub-solar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO2 production. An excess of measured water production, with respect to the value calculated using a simple thermo-physical model, is observed when the head lobe and regions of the Southern hemisphere with strong seasonal variations are illuminated. A drastic decrease in dust production, when the water production (both measured and from the model) displays a maximum, happens when typical Northern consolidated regions are illuminated and the Southern hemisphere regions with strong seasonal variations are instead in shadow.
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