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3D thermal modeling of two selected regions on comet 67P and comparison with Rosetta/MIRO measurements

机译：彗星67P上两个选定区域的3D热建模以及与Rosetta / MIRO测量的比较

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Context. The Microwave Instrument for the Rosetta Orbiter (MIRO) was one of the key instruments of the Rosetta mission, which acquired a wealth of data, in particular as the orbiter moved in the close environment of comet 67P/Churyumov-Gerasimenko (August 2014–September 2016). It was the only instrument of the Rosetta payload that was able to measure temperatures in the near-subsurface layers of the cometary nucleus down to a depth of some centimeters. This range is most relevant for understanding the mechanisms of cometary activity. Aims. We simulate the 3D temperature distribution for two selected regions that were observed by MIRO in March 2015 when the comet was at a distance of about 2 au from the Sun. The importance of a full 3D treatment for a realistic subsurface temperature distribution and the thermal heat balance in the uppermost subsurface is investigated in comparison with analogous 1D simulations. Methods. For this purpose, we developed a numerical heat transfer model of the surface as well as the near-subsurface regions. It enabled us to solve the heat transfer equation in the subsurface volume with appropriate radiation boundary conditions taken into account. The comparison with 1D simulations was made on the basis of the same solar irradiation history. Results. Although the temperature gradient is predominantly normal to the comet surface, we still find that tangential flows may be responsible for local temperature differences of up to 30 K (a few Kelvin on the average) in the uppermost subsurface layers. From the results of the 3D simulations, we calculated the MIRO antenna temperature. A comparison with the actual measurements shows good agreement for the MIRO submillimeter channel, but there is a notable discrepancy for the millimeter channel. This last assessment is not related to the use of the 3D model; potential causes are discussed in some detail with a view to future studies.
机译：上下文。罗塞塔轨道器微波仪器（MIRO）是罗塞塔任务的关键仪器之一，该仪器获得了大量数据，尤其是当轨道器在67P / Churyumov-Gerasimenko彗星的近距离环境中移动时（2014年8月至9月） 2016）。它是罗塞塔有效载荷中唯一能够测量彗核近地下层温度直至几厘米深度的仪器。此范围与了解彗星活动的机制最相关。目的我们模拟了MIRO在2015年3月观察到的两个选定区域的3D温度分布，当时彗星距离太阳约2 au。与类似的一维模拟相比，研究了完整的3D处理对于逼真的地下温度分布和最上层地下热平衡的重要性。方法。为此，我们开发了表面以及近地下区域的数值传热模型。它使我们能够在考虑适当的辐射边界条件的情况下求解地下体积中的传热方程。基于相同的太阳辐射历史，与一维模拟进行了比较。结果。尽管温度梯度主要垂直于彗星表面，但我们仍然发现，切向流可能是最上层次表层局部温差高达30 K（平均几个开尔文）的原因。根据3D模拟的结果，我们计算了MIRO天线温度。与实际测量值的比较表明，对于MIRO亚毫米通道，它具有良好的一致性，但是毫米通道存在显着差异。最后的评估与3D模型的使用无关;为了将来的研究，对潜在的原因进行了详细的讨论。

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