Observations and inversion of the eigenfrequencies of free oscillations constitute powerful tools to investigate the internal structure of a planet. On Mars, such free oscillations can be excited by atmospheric pressure and wind stresses from the Martian atmosphere, analogous to what occurs on Earth. Over long periods and on a global scale, this phenomenon may continuously excite Mars’ background free oscillations (MBFs), which constitute the so-called Martian hum. However, the source exciting MBFs is related both to the global-scale atmospheric circulation on Mars and to the variations in pressure and wind at the planetary boundary layer, for which no data are available.To overcome this drawback, we focus herein on a global-scale source and use results of simulations based on General Circular Models (GCMs). GCMs can predict and reproduce long-term, global-scale Martian pressure and wind variations and suggest that, contrary to what happens on Earth, daily correlations in the Martian hum might be generated by the solar-driven GCM. After recalling the excitation terms, we calculate MBFs by using GCM computations and estimate the contribution to the hum made by the global atmospheric circulation. Although we work at the lower limit of MBF signals, the results indicate that the signal is likely to be periodic, which would allow us to use more efficient stacking theories than can be applied to Earth’s hum. We conclude by discussing the perspectives for the InSight SEIS instrument to detect the Martian hum. The amplitude of the MBF signal is on the order of nanogals and is therefore hidden by instrumental and thermal noise, which implies that, provided the predicted daily coherence in hum excitation is present, the InSight SEIS seismometer should be capable of detecting the Martian hum after monthly to yearly stacks.

中文翻译：

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火星的背景自由振荡

自由振荡特征频率的观测和反演构成了研究行星内部结构的有力工具。在火星上，这种自由振荡可以被来自火星大气的大气压力和风应力激发，类似于地球上发生的情况。在长期和全球范围内，这种现象可能会持续激发火星的背景自由振荡（MBF），这构成了所谓的火星嗡嗡声。然而，令人兴奋的 MBFs 源与火星上的全球尺度大气环流以及行星边界层的压力和风的变化有关，没有可用的数据。为了克服这个缺点，我们在此关注全球- 基于通用循环模型 (GCM) 的模拟的规模来源和使用结果。GCM 可以预测和再现长期的、全球尺度的火星压力和风的变化，并表明与地球上发生的情况相反，火星嗡嗡声的日常相关性可能是由太阳能驱动的 GCM 产生的。在回忆激发项后，我们通过使用 GCM 计算来计算 MBF，并估计全球大气环流对嗡嗡声的贡献。尽管我们在 MBF 信号的下限下工作，但结果表明该信号可能是周期性的，这将使我们能够使用比应用于地球嗡嗡声更有效的叠加理论。我们最后讨论了 InSight SEIS 仪器检测火星嗡嗡声的前景。MBF 信号的幅度在纳加仑量级，因此被仪器和热噪声隐藏，这意味着，