A key objective for the future exploration of the icy moon Enceladus is the characterization of the habitable conditions in its internal ocean. Radio science instrumentation on board a spacecraft in a low-altitude orbit about Enceladus would enable gravity measurements that are fundamental to providing constraints on its internal structure. We present here the concept of operations and expected results of the gravity investigation for a New Frontiers–class mission. Numerical simulations are carried out to determine the gravity field in spherical harmonics to degree and order 30 and the Love number k ₂ and its phase. By combining Enceladus’s shape measured by Cassini and the geophysical constraints obtained through the processing of the simulated radio science data, a Bayesian inference network is used for the interior model inversion. Our results indicate that the gravity investigation would enable tight constraints on core radius and density, ocean depth and density, and ice shell rigidity. By assuming a high core rigidity and a preliminary modeling of dissipation in the ice shell, our interior model inversion also yields information on the ice shell viscosity. Further data on the hydrosphere properties might be gathered through optical navigation data by accurately measuring Enceladus’s orientation model.

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描述土卫二海洋和内部特征的重力调查

未来探索冰卫星土卫二的一个关键目标是表征其内部海洋的宜居条件。围绕土卫二的低空轨道上的航天器上的无线电科学仪器将能够进行重力测量，这对于限制其内部结构至关重要。我们在此介绍新前沿级任务的重力调查的操作概念和预期结果。进行数值模拟以确定 30 阶球谐函数中的重力场以及洛夫数k ₂及其阶段。结合卡西尼号测量的土卫二形状和通过模拟无线电科学数据处理获得的地球物理约束，使用贝叶斯推理网络进行内部模型反演。我们的结果表明，重力研究将能够严格限制核心半径和密度、海洋深度和密度以及冰壳刚性。通过假设高核心刚度和冰壳中耗散的初步建模，我们的内部模型反演还产生了有关冰壳粘度的信息。有关水圈特性的进一步数据可以通过精确测量土卫二的方向模型通过光学导航数据来收集。