The plasma in the solar wind meeting the heliopause

The solar wind is a stream of charged particles—a plasma—that are ejected from the upper atmosphere of the sun. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the A stream is a body of Water with a current, confined within a bed and stream-banks In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound The stellar atmosphere is the outer region of the volume of a Star, lying above the Stellar core, Radiation zone and Convection zone. The Sun (Sol is the Star at the center of the Solar System. It consists mostly of electrons and protons with energies of about 1 keV. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive These particles are able to escape the sun's gravity, in part because of the high temperature of the corona, but also because of high kinetic energy that particles gain through a process that is not well-understood at this time. Gravitation is a natural Phenomenon by which objects with Mass attract one another Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The kinetic energy of an object is the extra Energy which it possesses due to its motion

Many phenomena are directly related to the solar wind, including geomagnetic storms that can knock out power grids on Earth, the aurorae such as the Northern Lights, and the plasma tails of comets that always point away from the sun. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — While early models of the solar wind used primarily thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. A thermal column (or thermal) is a column of rising Air in the lower altitudes of the Earth's atmosphere. An additional unknown acceleration mechanism is required, and likely relates to magnetic fields in the solar atmosphere. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges

History

The concept of streams of particles flowing outward from the Sun was first suggested by British amateur astronomer Richard C. Carrington. Richard Christopher Carrington ( May 26 1826 &ndash November 27 1875) was an English amateur Astronomer who discovered In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare. A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares This is a sudden outburst of energy from the Sun's atmosphere. On the following day, a geomagnetic storm was observed, and Carrington suspected that there may be a connection. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. George Fitzgerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days. George Francis FitzGerald ( 3 August 1851 &ndash 21 February 1901) was an Irish professor of "natural and experimental philosophy" ^[1]

Laboratory simulation of the magnetosphere's influence on the Solar Wind; these auroral-like Birkeland currents were created in a terrella, a magnetised anode globe in an evacuated chamber. A Birkeland current is a specific magnetic field aligned current in the Earth’s Magnetosphere which flows from the Magnetotail towards the Earth on the dawn side A terrella (meaning "little earth" is a small magnetised model ball representing the Earth, that is thought to have been invented by Englishman

The ideas of Fitzgerald and others was further developed by the Norwegian physicist Kristian Birkeland. Norway ( Norwegian: Norge ( Bokmål) or Noreg ( Nynorsk) officially the Kingdom of Norway, is a Constitutional Kristian Olaf Birkeland ( December 13, 1867 - June 15, 1917) was born in Christiania ( Oslo today and wrote his first His geomagnetic surveys showed that auroral activity was nearly permanent. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". ^[1] In 1916, Birkeland was probably the first person to successfully predict that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds". In other words, the solar wind consists of both negative electrons and positive ions. ^[2] Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun. Frederick Alexander Lindemann 1st Viscount Cherwell PC CH was an English Physicist who was an influential scientific adviser to the British ^[3]

Around the 1930s, scientists had determined that the temperature of the solar corona must be a million degrees Celsius because of the way it stood out into space (as seen during total eclipses). A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily Later spectroscopic work confirmed this extraordinary temperature. In the mid-1950s the British mathematician Sydney Chapman calculated the properties of a gas at such a temperature and determined it was such a superb conductor of heat that it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, a German scientist named Ludwig Biermann became interested in the fact that no matter whether a comet is headed towards or away from the sun, its tail always points away from the Sun. Ludwig Franz Benedict Biermann (Born on March 13 1907 in Hamm &ndash January 12 1986 in München) was a German A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. ^[4]

Eugene Parker realised that the heat flowing from the sun in Chapman's model and the comet tail blowing away from the sun in Biermann's hypothesis had to be the result of the same phenomenon, which he termed the "solar wind". Eugene N Parker (born 10 June, 1927) is an American solar Astrophysicist who received his B ^[5][6] Parker showed that even though the sun's corona is strongly attracted by solar gravity, it is such a good conductor of heat that it is still very hot at large distances. Since gravity weakens as distance from the sun increases, the outer coronal atmosphere escapes supersonically into interstellar space. Furthermore, Parker was the first person to notice that the weakening effect of the gravity has the same effect on hydrodynamic flow as a de Laval nozzle: it incites a transition from subsonic to supersonic flow. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion A de Laval Nozzle (or convergent-divergent nozzle, CD nozzle or con-di nozzle) is a tube that is pinched in the middle making an hourglass-shape For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 ^[7]

Opposition to Parker's hypothesis on the solar wind was strong. The paper he submitted to the Astrophysical Journal in 1958 was rejected by two reviewers. The Astrophysical Journal (abbreviated to ApJ or Astrophys J) is a Scientific journal covering Astronomy and Astrophysics. It was saved by the editor Subrahmanyan Chandrasekhar (who later received the 1983 Nobel Prize in physics). Padma Vibhushan Subrahmanyan Chandrasekhar, FRS ( Tamil: சுப்பிரமணியன் சந்திரசேகர் English ˌtʃʌndrəˈʃeɪkɑr( The Nobel Prize (Nobelpriset (Nobelprisen is a Swedish prize established in the 1895 will of Swedish chemist Alfred Nobel; it was first awarded in Peace, Literature

In January 1959, the first ever direct observations and measurements of strength of the solar wind were made by the Soviet satellite Luna 1. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Luna 1 (E-1 series also known as Mechta (Мечта lit: Dream) was the first Spacecraft to reach the vicinity ^[8] They were performed using scintillation counters and gaseous ionization detectors. A scintillation counter measures Ionizing radiation. The Sensor, called a Scintillator, consists of a transparent Crystal, usually phosphor In Particle physics, gaseous ionization detectors are detectors designed to seek the presence of particles (a Particle detector) ^[9] The discovery, made by Konstantin Gringauz was verified by Luna 2, Luna 3 and by the more distant measurements of Venera 1. Luna 2 (E-1A series was the second of the Soviet Union's Luna program spacecraft launched in the direction of the Moon. The Soviet spaceprobe Luna 3 (E-3 series was the third spacecraft sent successfully to the Moon and was an early triumph in the human exploration of outer space February 12 1961, 003436 UTC, the first planetary probe was launched to Venus by the Soviet Union. Three years later its measurement was performed by Americans (Neugebauer and collaborators) using the Mariner 2 spacecraft. Mariner 2 (Mariner-Venus 1962 a space probe to Venus, was the first successful Spacecraft in the NASA Mariner program. ^[10]

However, the acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. The first numerical simulation of the solar wind in the solar corona including closed and open field lines was performed by Pneuman and Knopp in 1971. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration. Magnetohydrodynamics (MHD ( magnetofluiddynamics or hydromagnetics) is the Academic discipline which studies the dynamics of electrically Steady state is a more general situation than Dynamic equilibrium. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a ^[11]

In the late 1990s the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the sun, and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. The Solar and Heliospheric Observatory ( SOHO) is a Spacecraft that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about 4 solar radii from the photosphere; but the transition (or "sonic point") now appears to be much lower, perhaps only 1 solar radius above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the sun. For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1

Wilfried Schröder has shown in his book " Who first discovered the solar wind" that the German astronomer Paul Ahnert gave the first fundamental insight in the existence of a permanent solar influence (wind) following the tail observations of the comet Whipple-Fedke (1942g), see for details: Wilfried Schröder Who first discovered the solar wind? Beiträge Geschichte Geophysik und Kosmische Physik, Volume IX, 2008, No. 3.

Emission

The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a million Kelvin. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily As a result of thermal collisions, the particles within the corona have a range of speeds described by a Maxwellian distribution. The Maxwell–Boltzmann distribution is a Probability distribution with applications in Physics and Chemistry. The mean velocity of these particles is about 145 km/s, which is well below the solar escape velocity of 618 km/s. However, a few of the particles will achieve energies sufficient to reach the terminal velocity of 400 km/s, allowing them to feed the solar wind. ^[12]

The total particles carried away from the Sun by the solar wind is about 1. 3×10³¹ per second. ^[13] The total mass loss each year is about (2–3)×10^-14 solar masses,^[14] or 6. The solar mass is a standard way to express Mass in Astronomy, used to describe the masses of other Stars and galaxies. 7 billion tons per hour. Units of mass There are three similar units of Mass called the ton: Long ton (simply ton in countries such as the United This is equivalent to losing a mass equal to the Earth every 150 million years. ^[15] However, only about 0. 01% of the Sun's total mass has been lost through the solar wind. ^[16] Other stars have much stronger stellar winds that result in significantly higher mass loss rates. A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a Star.

Components

The solar wind is divided into two components, respectively termed the slow solar wind and the fast solar wind. The slow solar wind has a velocity of about 400 km/s, a temperature of 1. 4–1. 6×10⁶ K and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of 750 km/s, a temperature of 8×10⁵ K and it nearly matches the composition of the Sun's photosphere. ^[17] The slow solar wind is twice as dense and more variable in intensity than the fast solar wind. The slow wind also has a more complex structure, with turbulent regions and large-scale structures. ^[18][13]

The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt". Coronal streamers extend outward from this region, carrying plasma from the interior along closed magnetic loops. ^[19][20] Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred between latitudes of 30–35° around the equator during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the minimum waned. Solar minimum is the period of least solar activity in the Solar cycle of the Sun. By the time of the solar maximum, the poles were also emitting a slow solar wind. Solar maximum or solar max is the period of greatest solar activity in the Solar cycle of the Sun. ^[21]

The fast solar wind is thought to originate from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field. Coronal holes are areas where the Sun's Corona is darker colder and has lower-density plasma than average In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges ^[22] Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. A convection cell is a phenomenon of Fluid dynamics that occurs in situations where there are Temperature differences within a body of Liquid or These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 kilometers above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect. ^[23]

Coronal Mass Ejection

Main article: Coronal Mass Ejection

Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called interplanetary coronal mass ejections, or ICMEs. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. ICMEs are the interplanetary manifestation of solar coronal mass ejections, which are caused by release of magnetic energy at the sun. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. ICMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares ICMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation) that precede the ICME. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J Image talkNew_radiation_symbol_ISO_21482svg for details --> Ionizing radiation

When an ICME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. ICME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora. Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the

ICMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the sun. Faster-moving streams tend to overtake slower streams that originate westward of them on the sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, ICMEs. This article refers to the cardinal direction for other uses see West (disambiguation.

Effect on the Solar System

Main article: Space weather

Over the lifetime of the Sun, the surface rotation rate has decreased significantly. Space weather is the concept of changing environmental conditions in Outer space. This loss of rotation is thought to have been caused by interaction of the Sun's surface layers with the escaping solar wind. ^[24]

Magnetospheres

Main article: Magnetosphere

Earth itself is nominally protected from the solar wind by its magnetic field, which deflects charged particles but also serves as an electromagnetic energy transmission line to the Earth's upper atmosphere and ionosphere in the auroral zones. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Earth 's magnetic field (and the surface magnetic field) is approximately a Magnetic dipole, with one pole near the North pole (see The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation We only notice the solar wind when it is strong enough for this energy to produce phenomena such as the aurora and geomagnetic storms. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. Bright auroras strongly heat the ionosphere, causing its plasma to expand into the magnetosphere, increasing the size of the plasma geosphere, and causing escape of atmospheric matter into the solar wind. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation The term Geosphere is often used to refer to the densest parts of Earth which consist mostly of rock and Regolith. Geomagnetic storms result when the pressure of plasmas contained inside the magnetosphere is sufficiently large to inflate and thereby distort the geomagnetic field. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather.

The solar wind is responsible for the overall shape of Earth's magnetosphere, and fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind. For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called A geosynchronous orbit is an Orbit around the Earth with an Orbital period matching the Earth's sidereal rotation period These phenomena are collectively called space weather. Space weather is the concept of changing environmental conditions in Outer space.

Atmospheres

Planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind.

Venus, the nearest planet to Earth, has an atmosphere 100 times more dense than our own. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University Modern space probes have discovered a comet-like tail that stretches back to the orbit of the Earth. ^[25]

Mars is larger than Mercury and four times farther from the sun, and yet even here it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a layer 100 times less dense than the Earth's.

Surface

Mercury, the nearest planet to the Sun, bears the full brunt of the solar wind, and its atmosphere is vestigial and transient, its surface bathed in radiation.

The Earth's Moon has no atmosphere or intrinsic magnetic field, and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to sample the solar wind, and lunar soil returned for study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. There has been speculation that these elements may prove to be useful resources for future lunar colonies.

Outer limits

Main article: Heliopause

The solar wind "blows a bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause, and is often considered to be the outer "border" of the solar system. The heliosphere is a bubble in space "blown" into the Interstellar medium (the hydrogen and helium gas that permeates the Galaxy) by the The distance to the heliopause is not precisely known, and probably varies widely depending on the current velocity of the solar wind and the local density of the interstellar medium, but it is known to lie far outside the orbit of Pluto. Scientists hope to gain more perspective on the heliopause from data acquired through the Interstellar Boundary Explorer (IBEX) mission, to be launched in 2008. The Interstellar Boundary Explorer ( IBEX) is a NASA

See also

Notes

External links

• Sun|trek website An educational resource for teachers and students about the Sun and its effect on the Earth