The Magnetosphere of Saturn

2018 ◽  
Author(s):  
Sarah Badman
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Rotation Axis ◽  
Planetary Science ◽  
Rotating Magnetic Field ◽  
Forthcoming Article ◽  
Azimuthal Component ◽  
Inner Magnetosphere ◽  
The Magnetic Field

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. Saturn’s magnetosphere is the region of space surrounding Saturn that is controlled by the planetary magnetic field. Saturn’s magnetic field is aligned to within 1 degree of the rotation axis and rotates with a period of ~10.7 h. The magnetosphere is compressed on the dayside by the impinging solar wind, and stretched into a long magnetotail on the nightside. Its surface, the magnetopause, is located where the internal and external plasma and magnetic pressures balance. As a result of the pressure distributions, the magnetopause has a bimodal distribution of standoff distance at the sub-solar point and is flattened over the poles relative to the equator. Radiation belts composed of trapped energetic electrons and protons are present in the inner magnetosphere. Their intensity is limited by the moons and rings that can absorb the energetic particles. The icy moons and rings, particularly the cryovolcanic moon Enceladus, are the main sources of mass in the form of water. When the water molecules are ionized they are confined to the equatorial plane by the rapidly rotating magnetic field. This mass-loading acts to distend the magnetic field lines from a dipolar configuration into a radially stretched magnetodisk, with an associated eastward-directed current. In situ measurements of plasma velocity indicate it generally lags behind the planetary rotation, introducing an azimuthal component of the magnetic field. Despite the alignment of the magnetic and rotation axes, so-called planetary period oscillations are ubiquitous in field and plasma measurements in the magnetosphere. Radial transport of plasma involves the centrifugal interchange instability in the inner magnetosphere and magnetic reconnection in the middle and outer magnetosphere. This allows mass from the moons and rings to be lost from the system. The outermost regions of the magnetosphere are also influenced by the surrounding solar wind through magnetic reconnection and viscous interactions. Acceleration via reconnection or other processes, or scattering of plasma into the atmosphere leads to auroral emissions detected at radio, infrared, visible, and ultraviolet wavelengths.

scholarly journals Magnetohydrodynamic simulations of a Uranus-at-equinox type rotating magnetosphere

2020 ◽  
Vol 633 ◽  
pp. A87 ◽  
Author(s):  
L. Griton ◽  
F. Pantellini
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Supersonic Flow ◽  
Magnetic Dipole ◽  
Stellar Wind ◽  
Rotation Axis ◽  
Spin Axis ◽  
Mhd Equations ◽  
Field Lines ◽  
The Magnetic Field

Context. As proven by measurements at Uranus and Neptune, the magnetic dipole axis and planetary spin axis can be off by a large angle exceeding 45°. The magnetosphere of such an (exo-)planet is highly variable over a one-day period and it does potentially exhibit a complex magnetic tail structure. The dynamics and shape of rotating magnetospheres do obviously depend on the planet’s characteristics but also, and very substantially, on the orientation of the planetary spin axis with respect to the impinging, generally highly supersonic, stellar wind. Aims. On its orbit around the Sun, the orientation of Uranus’ spin axis with respect to the solar wind changes from quasi-perpendicular (solstice) to quasi-parallel (equinox). In this paper, we simulate the magnetosphere of a fictitious Uranus-like planet plunged in a supersonic plasma (the stellar wind) at equinox. A simulation with zero wind velocity is also presented in order to help disentangle the effects of the rotation from the effects of the supersonic wind in the structuring of the planetary magnetic tail. Methods. The ideal magnetohydrodynamic (MHD) equations in conservative form are integrated on a structured spherical grid using the Message-Passing Interface-Adaptive Mesh Refinement Versatile Advection Code (MPI-AMRVAC). In order to limit diffusivity at grid level, we used background and residual decomposition of the magnetic field. The magnetic field is thus made of the sum of a prescribed time-dependent background field B0(t) and a residual field B1(t) computed by the code. In our simulations, B0(t) is essentially made of a rigidly rotating potential dipole field. Results. The first simulation shows that, while plunged in a non-magnetised plasma, a magnetic dipole rotating about an axis oriented at 90° with respect to itself does naturally accelerate the plasma away from the dipole around the rotation axis. The acceleration occurs over a spatial scale of the order of the Alfvénic co-rotation scale r*. During the acceleration, the dipole lines become stretched and twisted. The observed asymptotic fluid velocities are of the order of the phase speed of the fast MHD mode. In two simulations where the surrounding non-magnetised plasma was chosen to move at supersonic speed perpendicularly to the rotation axis (a situation that is reminiscent of Uranus in the solar wind at equinox), the lines of each hemisphere are symmetrically twisted and stretched as before. However, they are also bent by the supersonic flow, thus forming a magnetic tail of interlaced field lines of opposite polarity. Similarly to the case with no wind, the interlaced field lines and the attached plasma are accelerated by the rotation and also by the transfer of kinetic energy flux from the surrounding supersonic flow. The tailwards fluid velocity increases asymptotically towards the externally imposed flow velocity, or wind. In one more simulation, a transverse magnetic field, to both the spin axis and flow direction, was added to the impinging flow so that magnetic reconnection could occur between the dipole anchored field lines and the impinging field lines. No major difference with respect to the no-magnetised flow case is observed, except that the tailwards acceleration occurs in two steps and is slightly more efficient. In order to emphasise the effect of rotation, we only address the case of a fast-rotating planet where the co-rotation scale r* is of the order of the planetary counter-flow magnetopause stand-off distance rm. For Uranus, r*≫ rm and the effects of rotation are only visible at large tailwards distances r ≫ rm.

The Magnetosphere of Uranus

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.

scholarly journals Comparative Study on Planetary Magnetosphere in the Solar System

Sensors ◽  
2020 ◽  
Vol 20 (6) ◽  
pp. 1673
Author(s):  
Ching-Ming Lai ◽  
Jean-Fu Kiang
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Solar System ◽  
Comparative Study ◽  
Magnetic Reconnection ◽  
Tilt Angle ◽  
Planetary Magnetosphere ◽  
Field Distributions ◽  
Mhd Simulations ◽  
The Magnetic Field

The magnetospheric responses to solar wind of Mercury, Earth, Jupiter and Uranus are compared via magnetohydrodynamic (MHD) simulations. The tilt angle of each planetary field and the polarity of solar wind are also considered. Magnetic reconnection is illustrated and explicated with the interaction between the magnetic field distributions of the solar wind and the magnetosphere.

scholarly journals The Magnetic Field of Mercury

1977 ◽  
Vol 4 (1) ◽  
pp. 179-190
Author(s):  
Norman F. Ness
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Rotation Axis ◽  
Large Core ◽  
Crustal Rocks ◽  
Bow Shock Wave ◽  
The Usa ◽  
Global Magnetic Field ◽  
History Of ◽  
The Magnetic Field

The USA Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The 1st and 3rd encounters provided detailed observations of a well developed, detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field, and modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as Earth, tilted 12° from the rotation axis. The magnetic moment, 5×1022 Gauss-cm3, corresponds to an undistorted equatorial field intensity of 350γ, approximately 1% of Earth’s. The origin of the field, while unequivocally intrinsic to the planet, is uncertain. It may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. Among these possibilities, the latter appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature, differentiated planetary interior with a large core, Rc ≈ 0.7RM, and a record of the history of planetary formation in the magnetization of the crustal rocks.

Magnetic Curvature Analysis on Reconnection Related Structures at Earth’s Magnetopause

2020 ◽  
Author(s):  
Yi Qi ◽  
Christopher T. Russell ◽  
Robert J. Strangeway ◽  
Yingdong Jia ◽  
Roy B. Torbert ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Solar Wind Plasma ◽  
Radius Of Curvature ◽  
Plasma Properties ◽  
Magnetospheric Multiscale ◽  
Reconnection Site ◽  
Field Lines ◽  
The Magnetic Field

<p>Magnetic reconnection is a mechanism that allows rapid and explosive energy transfer from the magnetic field to the plasma. The magnetopause is the interface between the shocked solar wind plasma and Earth’s magnetosphere. Reconnection enables the transport of momentum from the solar wind into Earth’s magnetosphere. Because of its importance in this regard, magnetic reconnection has been extensively studied in the past and is the primary goal of the ongoing Magnetospheric Multiscale (MMS) mission. During magnetic reconnection, the originally anti-parallel fields annihilate and reconnect in a thinned current sheet. In the vicinity of a reconnection site, a prominently increased curvature of the magnetic field (and smaller radius of curvature) marks the region where the particles start to deviate from their regular gyro-motion and become available for energy conversion. Before MMS, there were no closely separated multi-spacecraft missions capable of resolving these micro-scale curvature features, nor examining particle dynamics with sufficiently fast cadence.</p><p>In this study, we use measurements from the four MMS spacecraft to determine the curvature of the field lines and the plasma properties near the reconnection site. We use this method to study FTEs (flux ropes) on the magnetopause, and the interaction between co-existing FTEs. Our study not only improves our understanding of magnetic reconnection, but also resolves the relationship between FTEs and structures on the magnetopause.</p>

scholarly journals On the role of rotation in the outflows of the Crab pulsar

2015 ◽  
Vol 24 (06) ◽  
pp. 1550042
Author(s):  
Gudavadze Irakli ◽  
Osmanov Zaza ◽  
Rogava Andria
Keyword(s):  
Magnetic Field ◽  
Rotation Axis ◽  
Three Dimensional ◽  
Rotating Magnetic Field ◽  
Crab Pulsar ◽  
X Ray ◽  
Field Lines ◽  
The Magnetic Field ◽  
Component Parallel

In order to study constraints imposed on kinematics of the Crab pulsar's jet, we consider motion of particles along co-rotating field lines in the magnetosphere of the Crab pulsar. It is shown that particles following the co-rotating magnetic field lines may attain velocities close to observable values. In particular, we demonstrate that if the magnetic field lines are within the light cylinder (LC), the maximum value of the velocity component parallel to the rotation axis is limited by 0.5c. This result in the context of the X-ray observations performed by Chandra X-ray Observatory seems to be quite indicative and useful to estimate the density of field lines inside the jet. Considering the three-dimensional (3D) field lines crossing the LC, we found that for explaining the force-free regime of outflows the magnetic field lines must asymptotically tend to the Archimedes spiral configuration. It is also shown that the 3D case may explain the observed jet velocity for appropriately chosen parameters of magnetic field lines.

scholarly journals Dynamics of the terrestrial radiation belts: a review of recent results during the VarSITI (Variability of the Sun and Its Terrestrial Impact) era, 2014–2018

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Shrikanth Kanekal ◽  
Yoshizumi Miyoshi
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Ring Current ◽  
Plasma Waves ◽  
Radiation Belts ◽  
The Sun ◽  
Plasma Convection ◽  
Outer Radiation Belt ◽  
Inner Magnetosphere

AbstractThe Earth’s magnetosphere is region that is carved out by the solar wind as it flows past and interacts with the terrestrial magnetic field. The inner magnetosphere is the region that contains the plasmasphere, ring current, and the radiation belts all co-located within about 6.6 Re, nominally taken to be bounding this region. This region is highly dynamic and is home to a variety of plasma waves and particle populations ranging in energy from a few eV to relativistic and ultra-relativistic electrons and ions. The interplanetary magnetic field (IMF) embedded in the solar wind via the process of magnetic reconnection at the sub-solar point sets up plasma convection and creates the magnetotail. Magnetic reconnection also occurs in the tail and is responsible for explosive phenomena known as substorms. Substorms inject low-energy particles into the inner magnetosphere and help generate and sustain plasma waves. Transients in the solar wind such as coronal mass ejections (CMEs), co-rotating interaction regions (CIRs), and interplanetary shocks compress the magnetosphere resulting in geomagnetic storms, energization, and loss of energetic electrons in the outer radiation belt nad enhance the ring current, thereby driving the geomagnetic dynamics. The Specification and Prediction of the Coupled Inner-Magnetospheric Environment (SPeCIMEN) is one of the four elements of VarSITI (Variability of the Sun and Its Terrestrial Impact) program which seeks to quantitatively predict and specify the inner magnetospheric environment based on Sun/solar wind driving inputs. During the past 4 years, the SPeCIMEN project has brought together scientists and researchers from across the world and facilitated their efforts to achieve the project goal. This review provides an overview of some of the significant scientific advances in understanding the dynamical processes and their interconnectedness during the VarSITI era. Major space missions, with instrument suites providing in situ measurements, ground-based programs, progress in theory, and modeling are briefly discussed. Open outstanding questions and future directions of inner magnetospheric research are explored.

scholarly journals Complexity of Magnetic-field Turbulence at Reconnection Exhausts in the Solar Wind at 1 au

2021 ◽  
Vol 923 (2) ◽  
pp. 132
Author(s):  
Rodrigo A. Miranda ◽  
Juan A. Valdivia ◽  
Abraham C.-L. Chian ◽  
Pablo R. Muñoz
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Magnetic Energy ◽  
Minimum Variance ◽  
Inertial Subrange ◽  
Order Structure ◽  
Entropy Index ◽  
Magnetic Field Turbulence ◽  
The Magnetic Field

Abstract Magnetic reconnection is a complex mechanism that converts magnetic energy into particle kinetic energy and plasma thermal energy in space and astrophysical plasmas. In addition, magnetic reconnection and turbulence appear to be intimately related in plasmas. We analyze the magnetic-field turbulence at the exhaust of four reconnection events detected in the solar wind using the Jensen–Shannon complexity-entropy index. The interplanetary magnetic field is decomposed into the LMN coordinates using the hybrid minimum variance technique. The first event is characterized by an extended exhaust period that allows us to obtain the scaling exponents of higher-order structure functions of magnetic-field fluctuations. By computing the complexity-entropy index we demonstrate that a higher degree of intermittency is related to lower entropy and higher complexity in the inertial subrange. We also compute the complexity-entropy index of three other reconnection exhaust events. For all four events, the B L component of the magnetic field displays a lower degree of entropy and higher degree of complexity than the B M and B N components. Our results show that coherent structures can be responsible for decreasing entropy and increasing complexity within reconnection exhausts in magnetic-field turbulence.

Flux tubes and energetic particles in Parker Solar Probe orbit 5: magnetic helicity - PVI method and ISOIS observations

2021 ◽  
Author(s):  
Francesco Pecora ◽  
Sergio Servidio ◽  
Antonella Greco ◽  
Stuart D. Bale ◽  
David J. McComas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Flux ◽  
Magnetic Reconnection ◽  
Energetic Particle ◽  
Plasma Turbulence ◽  
Small Scale ◽  
Flux Tubes ◽  
Particle Measurements ◽  
The Magnetic Field

<p>Plasma turbulence can be viewed as a magnetic landscape populated by large- and small-scale coherent structures, consisting notionally of magnetic flux tubes and their boundaries. Such structures exist over a wide range of scales and exhibit diverse morphology and plasma properties.  Moreover, interactions of particles with turbulence may involve temporary trapping in, as well as exclusion from, certain regions of space, generally controlled by the topology and connectivity of the magnetic field.  In some cases, such as SEP "dropouts'' the influence of the magnetic structure is dramatic; in other cases, it is more subtle, as in edge effects in SEP confinement. With Parker Solar Probe now closer to the sun than any previous mission, novel opportunities are available for examination of the relationship between magnetic flux structures and energetic particle populations. </p><p>We present a method that is able to characterize both the large- and small-scale structures of the turbulent solar wind, based on the combined use of a filtered magnetic helicity (H<sub>m</sub>) and the partial variance of increments (PVI). The synergistic combination with energetic particle measurements suggests whether these populations are either trapped within or excluded from the helical structure.</p><p>This simple, single-spacecraft technique exploits the natural tendency of flux tubes to assume a cylindrical symmetry of the magnetic field about a central axis. Moreover, large helical magnetic tubes might be separated by small-scale magnetic reconnection events (current sheets) and present magnetic discontinuity with the ambient solar wind. The method was first validated via direct numerical simulations of plasma turbulence and then applied to data from the Parker Solar Probe (PSP) mission. In particular, ISOIS energetic particle (EP) measurements along with FIELDS magnetic field measurements and SWEAP plasma moments, are enabling characterization of observations of EPs closer to their sources than ever before.<br> <br>This novel analysis, combining H<sub>m </sub>and PVI methods, reveals that a large number of flux tubes populate the solar wind and continuously merge in contact regions where magnetic reconnection and particle acceleration may occur. Moreover, the detection of boundaries, correlated with high-energy particle measurements, gives more insights into the nature of such helical structures as "excluding barriers'' suggesting a strong link between particle properties and fields topology. This research is partially supported by the Parker Solar Probe project. </p>

scholarly journals The Location of Magnetic Reconnection at Earth’s Magnetopause

2021 ◽  
Vol 217 (3) ◽  
Author(s):  
K. J. Trattner ◽  
S. M. Petrinec ◽  
S. A. Fuselier
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Reconnection ◽  
Ion Beams ◽  
Review Article ◽  
Observational Evidence ◽  
Magnetic Shear ◽  
General Direction ◽  
Shear Model ◽  
Wide Range

AbstractOne of the major questions about magnetic reconnection is how specific solar wind and interplanetary magnetic field conditions influence where reconnection occurs at the Earth’s magnetopause. There are two reconnection scenarios discussed in the literature: a) anti-parallel reconnection and b) component reconnection. Early spacecraft observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection X-line location with respect to the spacecraft. An improved view of the reconnection location at the magnetopause evolved from ionospheric emissions observed by polar-orbiting imagers. These observations and the observations of accelerated ion beams revealed that both scenarios occur at the magnetopause. Improved methodology using the time-of-flight effect of precipitating ions in the cusp regions and the cutoff velocity of the precipitating and mirroring ion populations was used to pinpoint magnetopause reconnection locations for a wide range of solar wind conditions. The results from these methodologies have been used to construct an empirical reconnection X-line model known as the Maximum Magnetic Shear model. Since this model’s inception, several tests have confirmed its validity and have resulted in modifications to the model for certain solar wind conditions. This review article summarizes the observational evidence for the location of magnetic reconnection at the Earth’s magnetopause, emphasizing the properties and efficacy of the Maximum Magnetic Shear Model.

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