The upper atmospheres of Uranus and Neptune

Melin, Henrik

doi:10.1098/rsta.2019.0478

Cited by 12 publications

(13 citation statements)

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“…While both emissions have been early discovered at Uranus [59,60], such as for Jupiter and Saturn, no detection has yet been achieved at Neptune yet [61, and references therein]. An exhaustive review on ice giant ionospheres and upper thermospheres is addressed in a companion paper [6], and we hereafter restrict ourselves to a brief discussion of H 3 + emissions and their suspected association with auroral processes at Uranus.…”

Section: Search At Other Wavelengthsmentioning

confidence: 99%

“…These pioneering observations, however, sampled a restricted time interval which corresponded to specific solar wind conditions and solar wind/magnetosphere configurations. Since the 1990s, Earth-based observations of both planets have been carried out to search for auroral signatures in the near-infrared (NIR, [6]), UV or X-ray ranges. Despite repeated efforts, only the Uranian UV aurorae were successfully re-observed at a couple of occasions by the Hubble Space Telescope (HST) past equinox.…”

Section: Introductionmentioning

confidence: 99%

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Auroral emissions from Uranus and Neptune

Lamy

2020

Phil. Trans. R. Soc. A.

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Uranus and Neptune possess highly tilted/offset magnetic fields whose interaction with the solar wind shapes unique twin asymmetric, highly dynamical, magnetospheres. These radiate complex auroral emissions, both reminiscent of those observed at the other planets and unique to the ice giants, which have been detected at radio and ultraviolet (UV) wavelengths to date. Our current knowledge of these radiations, which probe fundamental planetary properties (magnetic field, rotation period, magnetospheric processes, etc.), still mostly relies on Voyager 2 radio, UV and in situ measurements, when the spacecraft flew by each planet in the 1980s. These pioneering observations were, however, limited in time and sampled specific solar wind/magnetosphere configurations, which significantly vary at various timescales down to a fraction of a planetary rotation. Since then, despite repeated Earth-based observations at similar and other wavelengths, only the Uranian UV aurorae have been re-observed at scarce occasions by the Hubble Space Telescope. These observations revealed auroral features radically different from those seen by Voyager 2, diagnosing yet another solar wind/magnetosphere configuration. Perspectives for the in-depth study of the Uranian and Neptunian auroral processes, with implications for exoplanets, include follow-up remote Earth-based observations and future orbital exploration of one or both ice giant planetary systems. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems’.

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Section: Search At Other Wavelengthsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Auroral emissions from Uranus and Neptune

Lamy

2020

Phil. Trans. R. Soc. A.

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“…What processes generate and sustain them? And are they fundamentally different, or similar but highly variable? Can we remotely explore the ice giant magnetospheres via auroral observations from Earth orbiting telescopes (see [111,117])? Can observations of putative icy-moon auroral footpoints help to map their magnetic fields (as was done at Jupiter and Saturn)?…”

Section: Discussionmentioning

confidence: 99%

“…[116]), and future magnetospheric and auroral observations at Uranus and Neptune could provide key insights into their form and function. For a comprehensive discussion of the current knowledge from ultraviolet, infrared and radio emission observations, we direct the readers to the companion papers by [111,117].…”

Section: Auroramentioning

confidence: 99%

Ice giant magnetospheres

Paty

Arridge

Cohen

et al. 2020

Phil. Trans. R. Soc. A.

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The ice giant planets provide some of the most interesting natural laboratories for studying the influence of large obliquities, rapid rotation, highly asymmetric magnetic fields and wide-ranging Alfvénic and sonic Mach numbers on magnetospheric processes. The geometries of the solar wind–magnetosphere interaction at the ice giants vary dramatically on diurnal timescales due to the large tilt of the magnetic axis relative to each planet's rotational axis and the apparent off-centred nature of the magnetic field. There is also a seasonal effect on this interaction geometry due to the large obliquity of each planet (especially Uranus). With in situ observations at Uranus and Neptune limited to a single encounter by the Voyager 2 spacecraft, a growing number of analytical and numerical models have been put forward to characterize these unique magnetospheres and test hypotheses related to the magnetic structures and the distribution of plasma observed. Yet many questions regarding magnetospheric structure and dynamics, magnetospheric coupling to the ionosphere and atmosphere, and potential interactions with orbiting satellites remain unanswered. Continuing to study and explore ice giant magnetospheres is important for comparative planetology as they represent critical benchmarks on a broad spectrum of planetary magnetospheric interactions, and provide insight beyond the scope of our own Solar System with implications for exoplanet magnetospheres and magnetic reversals. This article is part of a discussion meeting issue ‘Future exploration of ice giant systems'.

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“…The difficulty in solving these problems lies in a lack of knowledge about the energy pathways in the strongly-coupled MIT system (well reviewed by Ray and Yates, 2021). Recent work has perhaps explained the effect as arising from wave-facilitated vertical momentum transport from the lower atmosphere at Saturn (Brown et al, 2020;Melin, 2020a;Melin, 2020b;O'Donoghue et al, 2021). Whether the same mechanism can explain the same crises at the other outer planets is unknown, and contributions from the magnetosphere cannot be ruled out at the time of writing.…”

Section: Magnetospherementioning

confidence: 99%

The Pulsating Magnetosphere at Jupiter

Manners¹,

Masters²

2020

Preprint

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The magnetosphere of Jupiter is the largest planetary magnetosphere in the solar system, and plays host to internal dynamics that remain, in many ways, mysterious. Prominent among these mysteries are the ultra-low-frequency (ULF) pulses ubiquitous in this system. Pulsations in the electromagnetic emissions, magnetic field and flux of energetic particles have been observed for decades, with little to indicate the source mechanism. While ULF waves have been observed in the magnetospheres of all the magnetized planets, the magnetospheric environment at Jupiter seems particularly conducive to the emergence of ULF waves over a wide range of periods (1-100+ minutes). This is mainly due to the high variability of the system on a global scale: internal plasma sources and a powerful intrinsic magnetic field produce a highly-compressible magnetospheric cavity, which can be reduced to a size significantly smaller than its nominal expanded state by variations in the dynamic pressure of the solar wind. Compressive fronts in the solar wind, turbulent surface interactions on the magnetopause and internal plasma processes can also all lead to ULF wave activity inside the magnetosphere.To gain the first comprehensive view of ULF waves in the Jovian system, we have performed a heritage survey of magnetic field data measured by six spacecraft that visited the magnetosphere (Galileo, Ulysses, Voyager 1 & 2 and Pioneer 10 & 11). We found several-hundred wave events consisting of wave packets parallel or transverse to the mean magnetic field, interpreted as fast-mode or Alfv&#233;nic MHD wave activity, respectively. Parallel and transverse events were often coincident in space and time, which may be evidence of global Alfv&#233;nic resonances of the magnetic field known as field-line-resonances. We found that 15-, 30- and 40-minute periods dominate the Jovian ULF wave spectrum, in agreement with the dominant &#8220;magic frequencies&#8221; often reported in existing literature.We will discuss potential driving mechanisms as informed by the results of the heritage survey, how this in turn affects our understanding of energy transfer in the magnetosphere, and potential investigations to be made using data from the JUNO spacecraft. We will also discuss the potential for multiple resonant cavities, and how the resonance modes of the Jovian magnetosphere may differ from those of the other magnetized planets.

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The upper atmospheres of Uranus and Neptune

Cited by 12 publications

References 47 publications

Auroral emissions from Uranus and Neptune

Auroral emissions from Uranus and Neptune

Ice giant magnetospheres

The Pulsating Magnetosphere at Jupiter

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