Ice giant system exploration in the 2020s: an introduction

Fletcher, Leigh N.; Simon-Miller, A. A.; Hofstadter, Mark; Arridge, C. S.; Cohen, I. J.; Masters, A.; Mandt, Kathleen; Coustenis, A.

doi:10.1098/rsta.2019.0473

“…Uranus and Neptune are still underexplored compared to the gas giants, and the scientific yield of prospective in-situ missions to these planets are being rigorously examined by the planetary science community (see e.g., Hofstadter et al 2019;Beddingfield et al 2020;Dahl et al 2020;Fletcher et al 2020aFletcher et al , 2020bHelled & Fortney 2020b;Moore et al 2020;Zwick et al 2022). Furthermore, various mission concepts have already been suggested (e.g., Cartwright et al 2020;Cohen et al 2020;Jarmak et al 2020;Simon et al 2020;Rymer et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Zonal Winds of Uranus and Neptune: Gravitational Harmonics, Dynamic Self-gravity, Shape, and Rotation

Soyuer

¹

,

Neuenschwander

²

,

Helled

³

2022

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Uranus and Neptune exhibit fast surface zonal winds that can reach up to a few hundred meters per second. Previous studies on zonal gravitational harmonics and ohmic dissipation constraints suggest that the wind speeds diminish rapidly in relatively shallow depths within the planets. Through a case-by-case comparison between the missing dynamical gravitational harmonic J 4 ′ from structure models, and with that expected from fluid perturbations, we put constraints on zonal wind decay in Uranus and Neptune. To this end, we generate polytropic empirical structure models of Uranus and Neptune using fourth-order theory of figures that leave hydrostatic J 4 as an open parameter. Allotting the missing dynamical contribution to density perturbations caused by zonal winds (and their dynamic self-gravity), we find that the maximum scale height of zonal winds are ∼2%–3% of the planetary radii for both planets. Allowing the models to have J 2 solutions in the ±5 × 10−6 range around the observed value has similar implications. The effect of self-gravity on J 4 ′ is roughly a factor of ten lower than that of zonal winds, as expected. The decay scale heights are virtually insensitive to the proposed modifications to the bulk rotation periods of Uranus and Neptune in the literature. Additionally, we find that the dynamical density perturbations due to zonal winds have a measurable impact on the shape of the planet, and could potentially be used to infer wind decay and bulk rotation period via future observations.

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“…Because of the large distances involved, the transfer times are very long, and even if an ice giant mission concept was selected by a space agency tomorrow, it would likely not arrive until the 2040s (e.g. [48]).…”

Section: Future Opportunitiesmentioning

confidence: 99%

The upper atmospheres of Uranus and Neptune

Melin

¹

2020

Phil. Trans. R. Soc. A.

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We review the current understanding of the upper atmospheres of Uranus and Neptune, and explore the upcoming opportunities available to study these exciting planets. The ice giants are the least understood planets in the solar system, having been only visited by a single spacecraft, in 1986 and 1989, respectively. The upper atmosphere plays a critical role in connecting the atmosphere to the forces and processes contained within the magnetic field. For example, auroral current systems can drive charged particles into the atmosphere, heating it by way of Joule heating. Ground-based observations of H 3 + provides a powerful remote diagnostic of the physical properties and processes that occur within the upper atmosphere, and a rich dataset exists for Uranus. These observations span almost three decades and have revealed that the upper atmosphere has continuously cooled between 1992 and 2018 at about 8 K/year, from approximately 750 K to approximately 500 K. The reason for this trend remain unclear, but could be related to seasonally driven changes in the Joule heating rates due to the tilted and offset magnetic field, or could be related to changing vertical distributions of hydrocarbons. H 3 + has not yet been detected at Neptune, but this discovery provides low-hanging fruit for upcoming facilities such as the James Webb Space Telescope and the next generation of 30 m telescopes. Detecting H 3 + at Neptune would enable the characterization of its upper atmosphere for the first time since 1989. To fully understand the ice giants, we need dedicated orbital missions, in the same way the Cassini spacecraft explored Saturn. Only by combining in situ observations of the magnetic field with in-orbit remote sensing can we get the complete picture of how energy moves between the atmosphere and the magnetic field. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

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“…The China Space Administration is also expected to start a Jupiter exploration program in 2030 18 . In addition, NASA is planning to launch a probe to explore Saturn in 2026 and to start the Neptune exploration program within the next 20 years 19 . Obviously, understanding the working mechanism of materials and equipment under supergravity is of great significance to the smooth development of the planetary exploration program.…”

Section: Introductionmentioning

confidence: 99%

Effect of the supergravity on the formation and cycle life of non-aqueous lithium metal batteries

Gao

¹

,

Qiao

²

,

You

³

et al. 2022

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Extra-terrestrial explorations require electrochemical energy storage devices able to operate in gravity conditions different from those of planet earth. In this context, lithium (Li)-based batteries have not been fully investigated, especially cell formation and cycling performances under supergravity (i.e., gravity > 9.8 m s−2) conditions. To shed some light on these aspects, here, we investigate the behavior of non-aqueous Li metal cells under supergravity conditions. The physicochemical and electrochemical characterizations reveal that, distinctly from earth gravity conditions, smooth and dense Li metal depositions are obtained under supergravity during Li metal deposition on a Cu substrate. Moreover, supergravity allows the formation of an inorganic-rich solid electrolyte interphase (SEI) due to the strong interactions between Li+ and salt anions, which promote significant decomposition of the anions on the negative electrode surface. Tests in full Li metal pouch cell configuration (using LiNi0.8Co0.1Mn0.1O2-based positive electrode and LiFSI-based electrolyte solution) also demonstrate the favorable effect of the supergravity in terms of deposition morphology and SEI composition and ability to carry out 200 cycles at 2 C (400 mA g−1) rate with a capacity retention of 96%.

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Ice giant system exploration in the 2020s: an introduction

Cited by 16 publications

References 56 publications

Zonal Winds of Uranus and Neptune: Gravitational Harmonics, Dynamic Self-gravity, Shape, and Rotation

Zonal Winds of Uranus and Neptune: Gravitational Harmonics, Dynamic Self-gravity, Shape, and Rotation

The upper atmospheres of Uranus and Neptune

Effect of the supergravity on the formation and cycle life of non-aqueous lithium metal batteries

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