The magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the boundary between the planet's magnetic field and the solar wind. The location of the magnetopause is determined by the balance between the pressure of the dynamic planetary magnetic field and the dynamic pressure of the solar wind. As the solar wind pressure increases and decreases, the magnetopause moves inward and outward in response. Waves along the magnetopause move in the direction of the solar wind flow in response to small-scale variations in the solar wind pressure and to Kelvin–Helmholtz instabilities.
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynamo.
The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between 0.5 and 10 keV. The composition of the solar wind plasma also includes a mixture of particle species found in the solar plasma: trace amounts of heavy ions and atomic nuclei of elements such as carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron. There are also rarer traces of some other nuclei and isotopes such as phosphorus, titanium, chromium, and nickel's isotopes 58Ni, 60Ni, and 62Ni. Superimposed with the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind is called the Alfvén surface.
An aurora , also commonly known as the northern lights or southern lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions. Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky.
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere. The term "space weather" was first used in the 1950s and popularized in the 1990s. Later, it prompted research into "space climate", the large-scale and long-term patterns of space weather.
The magnetosheath is the region of space between the magnetopause and the bow shock of a planet's magnetosphere. The regularly organized magnetic field generated by the planet becomes weak and irregular in the magnetosheath due to interaction with the incoming solar wind, and is incapable of fully deflecting the highly charged particles. The density of the particles in this region is considerably lower than what is found beyond the bow shock, but greater than within the magnetopause, and can be considered a transitory state.
The magnetosphere of Saturn is the cavity created in the flow of the solar wind by the planet's internally generated magnetic field. Discovered in 1979 by the Pioneer 11 spacecraft, Saturn's magnetosphere is the second largest of any planet in the Solar System after Jupiter. The magnetopause, the boundary between Saturn's magnetosphere and the solar wind, is located at a distance of about 20 Saturn radii from the planet's center, while its magnetotail stretches hundreds of Saturn radii behind it.
Cluster II was a space mission of the European Space Agency, with NASA participation, to study the Earth's magnetosphere over the course of nearly two solar cycles. The mission was composed of four identical spacecraft flying in a tetrahedral formation. As a replacement for the original Cluster spacecraft which were lost in a launch failure in 1996, the four Cluster II spacecraft were successfully launched in pairs in July and August 2000 onboard two Soyuz-Fregat rockets from Baikonur, Kazakhstan. In February 2011, Cluster II celebrated 10 years of successful scientific operations in space. In February 2021, Cluster II celebrated 20 years of successful scientific operations in space. As of March 2023, its mission was extended until September 2024. The China National Space Administration/ESA Double Star mission operated alongside Cluster II from 2004 to 2007.
A Birkeland current is a set of electrical currents that flow along geomagnetic field lines connecting the Earth's magnetosphere to the Earth's high latitude ionosphere. In the Earth's magnetosphere, the currents are driven by the solar wind and interplanetary magnetic field (IMF) and by bulk motions of plasma through the magnetosphere. The strength of the Birkeland currents changes with activity in the magnetosphere. Small scale variations in the upward current sheets accelerate magnetospheric electrons which, when they reach the upper atmosphere, create the Auroras Borealis and Australis.
Auroral kilometric radiation (AKR) is the intense radio radiation emitted in the acceleration zone of the polar lights. The radiation mainly comes from cyclotron radiation from electrons orbiting around the magnetic field lines of the Earth. The radiation has a frequency of between 50 and 500 kHz and a total power of between about 1 million and 10 million watts. The radiation is absorbed by the ionosphere and therefore can only be measured by satellites positioned at vast heights, such as the Fast Auroral Snapshot Explorer (FAST). According to the data of the Cluster mission, it is beamed out in the cosmos in a narrow plane tangent to the magnetic field at the source. The sound produced by playing AKR over an audio device has been described as "whistles", "chirps", and even "screams".
The magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the Pioneer 10 spacecraft in 1973.
The Magnetospheric Multiscale (MMS) Mission is a NASA robotic space mission to study the Earth's magnetosphere, using four identical spacecraft flying in a tetrahedral formation. The spacecraft were launched on 13 March 2015 at 02:44 UTC. The mission is designed to gather information about the microphysics of magnetic reconnection, energetic particle acceleration, and turbulence — processes that occur in many astrophysical plasmas. As of March 2020, the MMS spacecraft has enough fuel to remain operational until 2040.
The impact of the solar wind onto the magnetosphere generates an electric field within the inner magnetosphere - the convection field. Its general direction is from dawn to dusk. The co-rotating thermal plasma within the inner magnetosphere drifts orthogonal to that field and to the geomagnetic field Bo. The generation process is not yet completely understood. One possibility is viscous interaction between solar wind and the boundary layer of the magnetosphere (magnetopause). Another process may be magnetic reconnection. Finally, a hydromagnetic dynamo process in the polar regions of the inner magnetosphere may be possible. Direct measurements via satellites have given a fairly good picture of the structure of that field. A number of models of that field exists.
STEVE is an atmospheric optical phenomenon that appears as a purple and green light ribbon in the night sky, named in late 2016 by aurora watchers from Alberta, Canada. According to analysis of satellite data from the European Space Agency's Swarm mission, the phenomenon is caused by a 25 km (16 mi) wide ribbon of hot plasma at an altitude of 450 km (280 mi), with a temperature of 3,000 °C and flowing at a speed of 6 km/s (3.7 mi/s). The phenomenon is not rare, but had not been investigated and described scientifically prior to that time.
The Solar-Terrestrial Observer for the Response of the Magnetosphere (STORM) was one of five mission proposals selected to proceed to Phase A concept studies as part of the 2019 NASA Heliophysics Medium Class Explorer Announcement of Opportunity. STORM will provide the first-ever global view of the Sun-Earth system. STORM takes simultaneous observations of the solar wind and the response of Earth’s magnetosphere, including the magnetopause, auroral oval, and ring current dynamics, using global multi-spectral and neutral atom imaging to quantify the global circulation of the energy that powers space weather.
The Dungey cycle, officially proposed by James Dungey in 1961, is a phenomenon that explains interactions between a planet's magnetosphere and solar wind. Dungey originally proposed a cyclic behavior of magnetic reconnection between Earth's magnetosphere and flux of solar wind. This reconnection explained previously observed dynamics within Earth's magnetosphere. The rate of reconnection in the beginning of the cycle is dependent on the orientation of the interplanetary magnetic field as well as the resultant plasma conditions at the site of reconnection. On Earth, the reconnection cycle takes around 1 hour, but this differs from planet to planet.
Lynn Kistler is a physicist known for her research on the magnetosphere that protects Earth from radiation from space.
Patricia Reiff is an American space physicist at Rice University, known for her research on space weather and for engaging the public about science.
Michelle F. Thomsen is space physicist known for her research on the magnetospheres of Earth, Jupiter, and Saturn.
James Wynne Dungey (1923–2015) was a British space scientist who was pivotal in establishing the field of space weather and made significant contributions to the fundamental understanding of plasma physics.
![[Top] Simulation of SMILE soft X-ray images during a 52-hour orbital period. Pink rectangular boxes show two field-of-view candidates of the SMILE soft X-ray imager. [Bottom] SMLE orbit (pink ellipse), location (pink dots), and look direction (blue line) projected on the XZ plane (left), XY plane (middle), and YZ plane (right). Color contour shows plasma density on each planes. The OpenGGCM global magnetosphere - ionosphere model and one of SMILE orbit candidates are used for this simulation. Simulated SMILE soft X-ray images.gif](http://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Simulated_SMILE_soft_X-ray_images.gif/220px-Simulated_SMILE_soft_X-ray_images.gif)
