Expected constraints on Phobos interior from the MMX gravity and rotation observations

IF 2.5 2区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS
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Abstract

The origin of the Martian moons is still uncertain, and knowledge about their interior could provide support to some of its leading theories. In preparation for the JAXA Martian Moons eXploration (MMX) mission, we review our current knowledge on the interior of Phobos, and provide synthetic tests showing how the gravity and rotation determination could allow the detection of specific interior-structure properties. The inversion of the geodetic observables for the retrieval of the internal mass distribution of a set of synthetic interior models is performed via non-linear least-squares, where the interior parameterization is based on the level-set method. We additionally provide simple expressions allowing to relate some of these interior models to the geodetic observables of Phobos. The results, based on realistic measurement resolution and noise scenarios, show good retrievals for most of the models at the data resolutions expected from MMX. Specifically, we find the gravity information is realistically sufficient for the detection of mass anomalies below the Stickney crater, as well as large scale heterogeneous regions within plausible rubble-pile structures. Libration helps retrieve the more degenerate models for gravity, such as those with concentric layers or with density varying linearly with depth. The incremental improvement from further adding a hypothetical mean obliquity measurement is marginal. Finally, we apply the level-set inversion and the analytical formulas to estimate possible interior characteristics of the ‘real’ Phobos from the currently-available scarce geodetic observables. The level-set solutions for the real-data inversion generally converge to a higher mass concentration towards the surface in the equatorial region. Markov chain Monte Carlo estimations of parameters relative to a simple 2-layer model or a radial density distribution similarly hint at a lighter region inside of Phobos.
MMX重力和自转观测对火卫一内部的预期约束
火星卫星的起源仍不确定,对其内部的了解可以为一些主要理论提供支持。在为日本宇宙航空研究开发机构(JAXA)的火星卫星探索(MMX)任务做准备的过程中,我们回顾了我们目前对火卫一内部的了解,并提供了合成测试,显示重力和自转测定如何能够探测到特定的内部结构特性。通过非线性最小二乘法对大地测量观测数据进行反演,以检索一组合成内部模型的内部质量分布,其中内部参数化基于水平集方法。此外,我们还提供了简单的表达式,可以将其中一些内部模型与火卫一的大地测量观测数据联系起来。根据现实的测量分辨率和噪声情况得出的结果表明,在 MMX 预期的数据分辨率下,大多数模型的检索结果都很好。具体来说,我们发现重力信息足以探测到斯蒂克尼陨石坑下方的质量异常,以及可信碎石堆结构内的大尺度异质区域。重力校准有助于检索更为退化的重力模型,例如具有同心层或密度随深度线性变化的模型。进一步增加假定的平均倾角测量所带来的增量改进微乎其微。最后,我们应用水平集反演和分析公式,根据目前可用的稀缺大地测量观测数据来估计 "真实 "火卫一可能的内部特征。真实数据反演的水平集解一般都趋向于赤道区域向地表的较高质量浓度。马尔科夫链蒙特卡洛参数估计与简单的两层模型或径向密度分布相比较,同样暗示火卫一内部有一个较轻的区域。
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来源期刊
Icarus
Icarus 地学天文-天文与天体物理
CiteScore
6.30
自引率
18.80%
发文量
356
审稿时长
2-4 weeks
期刊介绍: Icarus is devoted to the publication of original contributions in the field of Solar System studies. Manuscripts reporting the results of new research - observational, experimental, or theoretical - concerning the astronomy, geology, meteorology, physics, chemistry, biology, and other scientific aspects of our Solar System or extrasolar systems are welcome. The journal generally does not publish papers devoted exclusively to the Sun, the Earth, celestial mechanics, meteoritics, or astrophysics. Icarus does not publish papers that provide "improved" versions of Bode''s law, or other numerical relations, without a sound physical basis. Icarus does not publish meeting announcements or general notices. Reviews, historical papers, and manuscripts describing spacecraft instrumentation may be considered, but only with prior approval of the editor. An entire issue of the journal is occasionally devoted to a single subject, usually arising from a conference on the same topic. The language of publication is English. American or British usage is accepted, but not a mixture of these.
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