Strong heterogeneities in the composition of the volatile species have been detected in the coma of comet 67P/Churyumov-Gerasimenko (67P/C-G) by the ROSINA instrument onboard the ESA’s Rosetta spacecraft. However, it is not clear if these heterogeneities are indicative of heterogeneities in the near-surface nucleus composition or if the coma composition is mainly insolation-driven. In order to clarify the link between the composition of the nucleus and the composition of the coma we have performed numerical simulations and compare our results with measurements acquired by ROSINA/DFMS for three major volatile species namely, H₂O, CO₂, and CO. We use a previously published thermo-physical numerical model designed to study cometary nucleus evolution, including volatile outgassing and internal stratigraphy, as the comet orbits the Sun. The model follows schemes used for much of the past three decades to model cometary outgassing. Our results match well the experimental volatiles density measurements of ROSINA/DFMS for most of the Rosetta mission. They suggest that the outgassing pattern is mainly insolation-driven and the variations are caused by the tilt of rotation axis and eccentricity of the nucleus. The nucleus shows to 1st order a homogeneous composition and therefore we can provide constraints on the bulk volatiles composition of 67P/C-G nucleus which is dominated by H₂O (91.4% ​± ​4.5%), then CO₂ (6.7% ​± ​3.5%) and CO in small amount (1.9% ​± ​1.2%). However, in details, a dichotomy in composition between the northern and southern hemispheres of the comet is revealed. A CO/CO₂ bulk composition ratio of about 0.6 ​± ​0.1 is required to reproduce the measurements from the northern hemisphere and about 0.2 ​± ​0.1 for the southern hemisphere. To match the data, the thermal properties of the nucleus surface must be modified by adding a thin desiccated dust mantle (~5 ​mm) for northern latitudes while this appears not to be necessary for southern latitudes. This may be related to the observed dichotomy in putative airfall deposits. We suspect that, because of thermal inertia, seasonally non-illuminated areas continue to outgas and influence the ROSINA measurements. This effect cannot be reproduced with the model. Therefore during some periods of the mission, the fits are not ideal. Finally, the outgassing of the different ices leads to a layered internal structure defined by the sublimation front of each ice and formation of harder layers close to the surface due to sublimation/condensation processes. However, the thermo-physical model overestimates the absolute volatiles production (mainly in the southern hemisphere) leading to an overestimation of the erosion rates. Further investigations will be performed to improve the thermo-physical model and the sensitivity analysis.

ESA的Rosetta航天器上的ROSINA仪器在67P / Churyumov-Gerasimenko彗星（67P / CG）的昏迷中发现了挥发性物质组成的强异质性。但是，尚不清楚这些异质性是否表示近表面核成分中的异质性，或者昏迷成分是否主要受日射驱动。为了阐明核的组成与昏迷的组成之间的联系，我们进行了数值模拟，并将我们的结果与ROSINA / DFMS对三种主要挥发性物质H ₂ O，CO _2的测量结果进行了比较。，以及CO。我们使用先前发布的热物理数值模型来研究彗星绕太阳运行时，彗核的演化，包括挥发性气体和内部地层学。该模型遵循了过去三十年来用于模拟彗星气体排放的方案。对于大多数Rosetta任务，我们的结果与ROSINA / DFMS的挥发物密度实验值非常吻合。他们认为出气模式主要是由日射驱动的，并且变化是由旋转轴的倾斜和原子核的偏心引起的。原子核显示一阶均质成分，因此我们可以对67P / CG原子核的整体挥发物成分提供限制，其主要成分为H ₂ O（91.4％±4.5％），然后是CO ₂（6.7％±3.5％）和少量的CO（1.9％±1.2％）。然而，详细地，揭示了彗星的北半球和南半球之间的二分法。CO / CO ₂要从北半球复制测量值，需要约0.6±0.1的整体组成比，对于南半球，则需要约0.2±0.1的体积组成比。为了匹配数据，必须通过为北纬增加一个薄的干燥的粉尘罩（〜5毫米）来修改核表面的热特性，而对于南纬似乎没有必要。这可能与观察到的假定空降沉积物的二分法有关。我们怀疑由于热惯性，季节性无光照的区域会继续排气并影响ROSINA的测量结果。该效果无法在模型中重现。因此，在执行任务的某些时期，这种配合并不理想。最后，不同冰块的放气会导致分层的内部结构，该内部结构由每个冰块的升华前沿确定，并由于升华/凝结过程而在靠近表面的位置形成较硬的层。但是，热物理模型高估了绝对挥发物的产生量（主要在南半球），导致高估了侵蚀速率。将进行进一步的研究以改善热物理模型和灵敏度分析。