Librations and obliquity of the largest moons of Uranus

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

Icarus Pub Date : 2024-11-17 DOI:10.1016/j.icarus.2024.116371

Rose-Marie Baland , Valerio Filice , Sébastien Le Maistre , Antony Trinh , Marie Yseboodt , Tim Van Hoolst

{"title":"Librations and obliquity of the largest moons of Uranus","authors":"Rose-Marie Baland , Valerio Filice , Sébastien Le Maistre , Antony Trinh , Marie Yseboodt , Tim Van Hoolst","doi":"10.1016/j.icarus.2024.116371","DOIUrl":null,"url":null,"abstract":"<div><div>Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity. We find that if the Uranian satellites were two-layer solid bodies, libration measurement accuracies from around 0.25 m for Oberon to around 6 m for Miranda would rule out the possibility of homogeneous interiors. In combination with independent estimates of the mean moment of inertia (MOI), libration measurements could also be used to detect the presence of an ocean, the measurement precision required for this depending on the actual value of the libration amplitude. To compute the obliquity, we first build series for the orbital precession of all five satellites with a secular perturbations model. With the exception of Miranda, we show that due to the mutual gravitational interactions between the satellites, the obliquity of the large Uranian moons exhibits relatively large periodic variations around the mean value. We find that an obliquity measurement accuracy from around 1 m for Ariel to around 400 m for Oberon can rule out the homogeneous case. The presence of an internal global ocean could allow a resonant amplification of the obliquity, facilitating its detection. If no such resonance occurs, the obliquity would be almost indistinguishable from that expected for a solid body. The effect of tidal deformations on the rotation of the small to medium-sized Uranian moons is showed to be limited. Librations would be reduced by up to 10% and obliquity increased by up to 15% for Titania and Oberon, the effects being negligible for Miranda.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"426 ","pages":"Article 116371"},"PeriodicalIF":2.5000,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Icarus","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0019103524004317","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ASTRONOMY & ASTROPHYSICS","Score":null,"Total":0}

引用次数: 0

Abstract

Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity. We find that if the Uranian satellites were two-layer solid bodies, libration measurement accuracies from around 0.25 m for Oberon to around 6 m for Miranda would rule out the possibility of homogeneous interiors. In combination with independent estimates of the mean moment of inertia (MOI), libration measurements could also be used to detect the presence of an ocean, the measurement precision required for this depending on the actual value of the libration amplitude. To compute the obliquity, we first build series for the orbital precession of all five satellites with a secular perturbations model. With the exception of Miranda, we show that due to the mutual gravitational interactions between the satellites, the obliquity of the large Uranian moons exhibits relatively large periodic variations around the mean value. We find that an obliquity measurement accuracy from around 1 m for Ariel to around 400 m for Oberon can rule out the homogeneous case. The presence of an internal global ocean could allow a resonant amplification of the obliquity, facilitating its detection. If no such resonance occurs, the obliquity would be almost indistinguishable from that expected for a solid body. The effect of tidal deformations on the rotation of the small to medium-sized Uranian moons is showed to be limited. Librations would be reduced by up to 10% and obliquity increased by up to 15% for Titania and Oberon, the effects being negligible for Miranda.

查看原文本刊更多论文

天王星最大卫星的天平和倾斜度

在太阳系中发现了几个海洋世界，以及行星科学和天体生物学十年调查（2023-2032 年）将天王星选为最优先目标之后，天王星最大的五颗卫星（米兰达、阿丽埃尔、翁布里埃尔、泰坦尼娅和奥伯龙）再次受到关注，因为它们也可能蕴藏着地表下的海洋。我们将评估自转测量如何帮助确认这些天体的内部分化，并探测内部海洋（如果有的话）。由于天王星对其同步卫星扁平形状的引力力矩具有时变性，因此同步卫星相对于其平均自转会发生天平摆动，并以非零斜度前倾。对于一系列内核为岩石、周围为水圈（固态或分为外层冰壳、下层为液态海洋）的内部模型，我们计算了它们的昼夜自转振幅和倾角。我们发现，如果天王星卫星是两层固体天体，那么从奥伯龙的约 0.25 米到米兰达的约 6 米的天平动测量精度将排除内部均质的可能性。结合平均惯性矩（MOI）的独立估计值，自由振动测量还可用于探测海洋的存在，其所需的测量精度取决于自由振动振幅的实际值。为了计算斜度，我们首先用一个世俗扰动模型建立了所有五颗卫星的轨道偏移序列。除米兰达卫星外，我们发现由于卫星间的相互引力作用，天王星大卫星的倾角在平均值附近呈现出相对较大的周期性变化。我们发现，从阿里尔的约 1 米到奥伯龙的约 400 米的斜度测量精度可以排除同质情况。内部全球海洋的存在可能会使倾斜度发生共振放大，从而有利于其探测。如果没有发生这种共振，钝度将与固体天体的预期钝度几乎没有区别。潮汐变形对天王星中小卫星旋转的影响是有限的。泰坦尼亚和奥伯龙的自转将减少最多 10%，斜度将增加最多 15%，米兰达的影响可以忽略不计。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

求助全文

约1分钟内获得全文求助全文

来源期刊

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.