Auroral emissions from Uranus and Neptune

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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The Magnetosphere of Uranus

Oxford Research Encyclopedia of Planetary Science ◽

10.1093/acrefore/9780190647926.013.166 ◽

2018 ◽

Author(s):

Xin Cao ◽

Carol Paty

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

High Speed ◽

Hubble Space Telescope ◽

Planetary Science ◽

Rotational Axis ◽

The Sun ◽

Forthcoming Article ◽

The North ◽

Voyager 2

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article. A magnetosphere is formed by the interaction between the magnetic field of a planet and the high-speed solar wind. Those planets with a magnetosphere have an intrinsic magnetic field such as Earth, Jupiter, and Saturn. Mars, especially, has no global magnetosphere, but evidence shows that a paleo-magnetosphere existed billions of years ago and was dampened then due to some reasons such as the change of internal activity. A magnetosphere is very important for the habitable environment of a planet because it provides the foremost and only protection for the planet from the energetic solar wind radiation. The majority of planets with a magnetosphere in our solar system have been studied for decades except for Uranus and Neptune, which are known as ice giant planets. This is because they are too far away from us (about 19 AU from the Sun), which means they are very difficult to directly detect. Compared to many other space detections to other planets, for example, Mars, Jupiter, Saturn and some of their moons, the only single fly-by measurement was made by the Voyager 2 spacecraft in the 1980s. The data it sent back to us showed that Uranus has a very unusual magnetosphere, which indicated that Uranus has a very large obliquity, which means its rotational axis is about 97.9° away from the north direction, with a relative rapid (17.24 hours) daily rotation. Besides, the magnetic axis is tilted 59° away from its rotational axis, and the magnetic dipole of the planet is off center, shifting 1/3 radii of Uranus toward its geometric south pole. Due to these special geometric and magnetic structures, Uranus has an extremely dynamic and asymmetric magnetosphere. Some remote observations revealed that the aurora emission from the surface of Uranus distributed at low latitude locations, which has rarely happened on other planets. Meanwhile, it indicated that solar wind plays a significant impact on the surface of Uranus even if the distance from the Sun is much farther than that of many other planets. A recent study, using numerical simulation, showed that Uranus has a “Switch-like” magnetosphere that allows its global magnetosphere to open and close periodically with the planetary rotation. In this article, we will review the historic studies of Uranus’s magnetosphere and then summarize the current progress in this field. Specifically, we will discuss the Voyager 2 spacecraft measurement, the ground-based and space-based observations such as Hubble Space Telescope, and the cutting-edge numerical simulations on it. We believe that the current progress provides important scientific context to boost future ice giant detection.

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Jupiter’s Aurora: Solar Wind and Rotational Influences

Highlights of Astronomy ◽

10.1017/s1539299600014362 ◽

2002 ◽

Vol 12 ◽

pp. 606

Author(s):

J. Hunter Waite ◽

John T. Clarke ◽

R.J. Walker ◽

John E.P. Connerney ◽

D. McComas ◽

...

Keyword(s):

Solar Wind ◽

Electric Fields ◽

Strong Field ◽

Heavy Ion ◽

Loss Cone ◽

X Ray ◽

Planetary Rotation ◽

Angle Scattering ◽

Auroral Emissions ◽

Atmospheric Loss

AbstractJovian auroral emissions are observed at infrared, visible, ultraviolet, and x-ray wavelengths. As at Earth, pitch-angle scattering of energetic particles into the atmospheric loss cone and the acceleration of current-carrying electrons in field-aligned currents both play a role in exciting the auroral emissions. The x-ray aurora is believed to result principally from heavy ion precipitation, while the ultraviolet aurora is produced predominantly by precipitating energetic electrons. The magnetospheric processes responsible for the aurora are driven primarily by planetary rotation. Acceleration of Iogenic plasma by rotationally-induced electric fields results in both the formation of the energetic ions that are scattered and the formation of strong, field-aligned currents that communicate the torques from the ionosphere. In addition to rotation-driven processes, solar-wind-modulated processes in the outer magnetosphere may lead to highly, time-dependent acceleration and thus also contribute to jovian auroral activity. Observational evidence for both sources will be presented. See Waite et al. (2001, Nat., 410, 787).

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Mars’ ionosphere: from our current knowledge to the way forward

10.5194/egusphere-egu21-5084 ◽

2021 ◽

Author(s):

Beatriz Sanchez-Cano

Keyword(s):

Solar Wind ◽

Space Weather ◽

Current Knowledge ◽

Conducting Layer ◽

Neutral Atmosphere ◽

Orbital Eccentricity ◽

Large Space ◽

Weather Events ◽

Martian Ionosphere

The ionosphere of Mars is the conducting layer embedded within the thermosphere and exosphere that is mostly the result of solar EUV photoionization. It is also the layer that links the neutral atmosphere with space, and acts as the main obstacle to the solar wind. The ionosphere&#8217;s interaction with the solar wind is a critical aspect that determines the Martian atmospheric evolution, and ultimately the planet&#8217;s habitability. This interaction is often referred to as planetary Space Weather, the forecast of which is currently challenging due to the lack of a permanent in-situ solar wind monitor at Mars. Understanding the ionospheric response to solar wind variability is, therefore, essential in order to assess the response of the Martian plasma environment to the dissipation of energy from solar storms, and their impact on current technology deployed on the red planet.This lecture will focus on our current knowledge of the Martian ionosphere. In particular, I will focus on our recent advances in the understanding of the Martian ionospheric reaction to different Space Weather events during the solar cycle, both from the data analysis and ionospheric modelling perspectives. Some important aspects to consider are the bow shock, magnetic pileup boundary, and ionopause characterization, as well as the behaviour of the topside and bottomside of the ionosphere taking into account the planet&#8217;s orbital eccentricity. Moreover, I will show the effect of electron precipitation from large Space Weather events in the very low Martian ionosphere, a region that it is not accessible to in-situ spacecraft observations. Finally, I will conclude the presentation by giving my perspective on some of the key outstanding questions that remain unknown, and I consider they constitute the next generation of Mars&#8217; ionospheric science and exploration.&#160;

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Relationship between solar wind corotating interaction regions and the phasing and intensity of Saturn kilometric radiation bursts

Annales Geophysicae ◽

10.5194/angeo-26-3641-2008 ◽

2008 ◽

Vol 26 (12) ◽

pp. 3641-3651 ◽

Cited By ~ 30

Author(s):

S. V. Badman ◽

S. W. H. Cowley ◽

L. Lamy ◽

B. Cecconi ◽

P. Zarka

Keyword(s):

Solar Wind ◽

Dynamic Pressure ◽

Rotation Period ◽

Corotating Interaction Regions ◽

Magnetic Field Data ◽

Radio Emissions ◽

Planetary Rotation ◽

Plasma Spectrometer ◽

Interaction Regions

Abstract. Voyager spacecraft measurements of Saturn kilometric radiation (SKR) identified two features of these radio emissions: that they pulse at a period close to the planetary rotation period, and that the emitted intensity is correlated with the solar wind dynamic pressure (Desch and Kaiser, 1981; Desch, 1982; Desch and Rucker, 1983). In this study the inter-relation between the intensity and the pulsing of the SKR is analysed using Cassini spacecraft measurements of the interplanetary medium and SKR over the interval encompassing Cassini's approach to Saturn, and the first extended orbit. Cassini Plasma Spectrometer ion data were only available for a subset of the dates of interest, so the interplanetary conditions were studied primarily using the near-continuously available magnetic field data, augmented by the ion moment data when available. Intense SKR bursts were identified when solar wind compressions arrived at Saturn. The intensity of subsequent emissions detected by Cassini during the compression intervals was variable, sometimes remaining intense for several planetary rotations, sometimes dimming and rarely disappearing. The timings of the initial intense SKR peaks were sometimes independent of the long-term pulsing behaviour identified in the SKR data. Overall, however, the pulsing of the SKR peaks during the disturbed intervals was not significantly altered relative to that during non-compression intervals.

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Magnetic fields and charged particles around major planets and their satellites

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1981.0199 ◽

1981 ◽

Vol 303 (1477) ◽

pp. 247-260 ◽

Cited By ~ 3

Keyword(s):

Solar Wind ◽

Large Scale ◽

Small Volume ◽

Magnetic Moments ◽

Charged Particles ◽

The Moon ◽

Planetary Rotation ◽

Spacecraft Data ◽

Insight Into

Jupiter and Saturn have magnetospheres whose large-scale structure can be understood by analogy with Earth, but the ways in which the magnetospheres differ are of great interest. At Earth, large-scale processes are dominated by convective plasma flows driven by the solar wind. At Jupiter, centrifugal effects driven by planetary rotation are critical. Magnetosphere particle sources include not only the ionosphere and the solar wind (as at Earth) but also satellites and rings. The internal planetary magnetic moments that control the scale of the magnetosphere differ by orders of magnitude between Jupiter and Earth. The magnetic moments have been modelled from spacecraft data but the restricted spatial sampling biases the results and limits confidence in details of the models. Because Jupiter is the only accessible protostar, it serves as a laboratory to test how well inferences from ground-based observations accord with in situ measurements. The agreement in some cases examined is reassuringly good but remote observations probe less than 0.1 % of the magnetospheric volume. Within that small volume, strong currents couple the moon lo with Jupiter s ionosphere. Voyager data give new insight into the lo story and suggest that lo may itself be magnetized and surrounded by an entirely unfamiliar type of magnetosphere.

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MHD simulations of an Uranus type rotating magnetosphere

10.5194/egusphere-egu2020-18905 ◽

2020 ◽

Author(s):

Filippo Pantellini ◽

Léa Griton

Keyword(s):

Solar Wind ◽

Rotation Axis ◽

Large Angle ◽

Rotation Period ◽

Ecliptic Plane ◽

Characteristic Relaxation Time ◽

Dipole Axis ◽

Mhd Simulations ◽

Planetary Rotation ◽

Magnetospheric Tail

The characteristic relaxation time of the Uranus magnetosphere is of the order &#160;of the planet's rotation period. This is also the case for Jupiter or Saturn. However, the specificity of Uranus (and to a lesser extent of &#160;Neptune) is that the rotation axis and the magnetic dipole axis are separated by &#160;a large angle (~60&#176;) the consequence of which is the development of a highly dynamic and complex magnetospheric tail. In addition, and contrary to all other planets of the solar system, the rotation axis of Uranus happens to be quasi-parallel to the ecliptic plane which also implies a strong variability of the magnetospheric structure as a function of the season. The magnetosphere of Uranus is thus a particularly challenging case for global plasma simulations, even in the frame of MHD. We present MHD simulations of a Uranus type magnetosphere at both equinox (solar wind is orthogonal to the planetary rotation axis) and solstice (solar wind is orthogonal to the planetary rotation axis) configurations. The main differences between the two configurations will be discussed.&#160;

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3D-Bioprinting Strategies Based on In Situ Bone-Healing Mechanism for Vascularized Bone Tissue Engineering

Micromachines ◽

10.3390/mi12030287 ◽

2021 ◽

Vol 12 (3) ◽

pp. 287

Author(s):

Ye Lin Park ◽

Kiwon Park ◽

Jae Min Cha

Keyword(s):

Tissue Engineering ◽

Bone Tissue Engineering ◽

Bone Tissue ◽

Bone Healing ◽

Critical Size ◽

Current Knowledge ◽

3D Bioprinting ◽

The Past ◽

Regeneration Processes

Over the past decades, a number of bone tissue engineering (BTE) approaches have been developed to address substantial challenges in the management of critical size bone defects. Although the majority of BTE strategies developed in the laboratory have been limited due to lack of clinical relevance in translation, primary prerequisites for the construction of vascularized functional bone grafts have gained confidence owing to the accumulated knowledge of the osteogenic, osteoinductive, and osteoconductive properties of mesenchymal stem cells and bone-relevant biomaterials that reflect bone-healing mechanisms. In this review, we summarize the current knowledge of bone-healing mechanisms focusing on the details that should be embodied in the development of vascularized BTE, and discuss promising strategies based on 3D-bioprinting technologies that efficiently coalesce the abovementioned main features in bone-healing systems, which comprehensively interact during the bone regeneration processes.

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