Cosmic ray

Cosmic ray

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Cosmic rays are energetic charged subatomic particles, originating from outer space
Outer space
Outer space is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos....

. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

. Most primary cosmic rays (those that enter the atmosphere from deep space) are composed of familiar stable subatomic particles that normally occur on Earth, such as protons, atomic nuclei, or electrons. However, a very small fraction are stable particles of antimatter
Antimatter
In particle physics, antimatter is the extension of the concept of the antiparticle to matter, where antimatter is composed of antiparticles in the same way that normal matter is composed of particles...

, such as positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...

s or antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....

s, and the precise nature of this remaining fraction is an area of active research.

About 89% of cosmic rays are simple proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s or hydrogen nuclei, 10% are helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 nuclei or alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s, and 1% are the nuclei of heavier elements. These nuclei constitute 99% of the cosmic rays. Solitary electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s (much like beta particle
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...

s, although their ultimate source is unknown) constitute much of the remaining 1%.

The variety of particle energies reflects the wide variety of sources. The origins range from processes on the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 (and presumably other stars as well), to as yet unknown physical mechanisms in the farthest reaches of the observable universe
Observable universe
In Big Bang cosmology, the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light from those objects has had time to reach us since the beginning of the cosmological expansion...

. There is evidence that very high energy cosmic rays are produced over far longer periods than the explosion of a single star or sudden galactic event, suggesting multiple accelerating processes that cover very long distances with regard to the size of stars. The obscure mechanism of cosmic ray production at galactic distances is partly a result of the fact that (unlike other radiations) magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

s in our galaxy and other galaxies bend cosmic ray direction severely, so that they arrive nearly randomly from all directions, hiding any clue of the direction of their initial sources. Cosmic rays can have energies of over 1020 eV, far higher than the 1012 to 1013 eV that Terrestrial particle accelerators can produce. There has been interest in investigating cosmic rays of even greater energies
Ultra-high-energy cosmic ray
In astroparticle physics, an ultra-high-energy cosmic ray or extreme-energy cosmic ray is a cosmic ray with an extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays....

.

Cosmic rays are enriched in lithium, beryllium, and boron with regard to the relative abundance of these elements in the universe compared to hydrogen and helium, and thus are thought to have a primary role in the synthesis of these three elements through the process of "cosmic ray nucleosynthesis
Nucleosynthesis
Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons . It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees...

". They also produce some so-called cosmogenic stable isotopes and radioisotopes on Earth, such as carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

. In the history of particle physics
Particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

, cosmic rays were the source of the discovery of the positron, muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...

, and pi meson. Cosmic rays compose a large part of natural background radiation
Background radiation
Background radiation is the ionizing radiation constantly present in the natural environment of the Earth, which is emitted by natural and artificial sources.-Overview:Both Natural and human-made background radiation varies by location....

 on Earth. Since the intensity of cosmic rays is much larger outside the Earth's atmosphere and magnetic field, it is expected to have a major impact on the design of spacecraft that can safely transport humans in interplanetary space.

Composition


Cosmic rays may broadly be divided into two categories: primary and secondary.
The cosmic rays that originate from astrophysical sources are primary cosmic rays; these primary cosmic rays interact with interstellar matter
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

 creating secondary cosmic rays. The Sun also emits low energy cosmic rays associated with solar flare
Solar flare
A solar flare is a sudden brightening observed over the Sun surface or the solar limb, which is interpreted as a large energy release of up to 6 × 1025 joules of energy . The flare ejects clouds of electrons, ions, and atoms through the corona into space. These clouds typically reach Earth a day...

s. Almost 90% of cosmic rays are proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s, about 9% are helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 nuclei (alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s) and nearly 1% are electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s. The ratio of hydrogen to helium nuclei (28%) is about the same as the primordial elemental abundance ratio of these elements (24%).

The remaining fraction is made up of the other heavier nuclei that are nuclear synthesis end products, products of the Big Bang
Big Bang
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the young Universe to cool and resulted in...

, primarily lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

, beryllium
Beryllium
Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

, and boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

. These light nuclei appear in cosmic rays in much greater abundance (~1%) than in the solar atmosphere, where their abundance is about 10−9% that of helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

.

This abundance difference is a result of the way secondary cosmic rays are formed. Carbon and oxygen nuclei collide with interstellar matter to form lithium, beryllium and boron in a process termed cosmic ray spallation
Cosmic ray spallation
Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from protons, alpha particles, and nuclei...

. Spallation is also responsible for the abundances of scandium
Scandium
Scandium is a chemical element with symbol Sc and atomic number 21. A silvery-white metallic transition metal, it has historically been sometimes classified as a rare earth element, together with yttrium and the lanthanoids...

, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, vanadium
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...

, and manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

 ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

s in cosmic rays produced by collisions of iron and nickel nuclei with interstellar matter
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

. See Natural Environmental Radioactivity.

Satellite experiments have found evidence of a few antiproton
Antiproton
The antiproton is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy....

s and positron
Positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron...

s in primary cosmic rays, although there is no evidence of complex antimatter atomic nuclei, such as anti-helium nuclei (anti-alpha) particles. Antiprotons arrive at Earth with a characteristic energy maximum of 2 GeV, indicating their production in a fundamentally different process from cosmic ray protons.

Flux


The flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...

 of incoming cosmic rays at the upper atmosphere is dependent on the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

, the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...

, and the energy of the cosmic rays.

The solar wind decelerates the incoming particles and blocks some of the particles with energies below about 1 GeV. The amount of solar wind is not constant due to changes in solar activity. Thus, the level of the cosmic ray flux varies with solar activity. The Earth's magnetic field deflects some of the cosmic rays, giving rise to the observation that the flux is apparently dependent on latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

, longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....

, and azimuth angle. The magnetic field lines deflect the cosmic rays towards the poles, giving rise to the aurora
Aurora (astronomy)
An aurora is a natural light display in the sky particularly in the high latitude regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere...

.

At distances of ~94 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

 from the Sun, the solar wind undergoes a transition, called the termination shock, from supersonic to subsonic speeds. The region between the termination shock and the heliopause acts as a barrier to cosmic rays, decreasing the flux at lower energies by about 90%.

In the past, it was believed that the cosmic ray flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...

 remained fairly constant over time. However, recent research suggests 1.5 to 2-fold millennium-timescale changes in the cosmic ray flux in the past forty thousand years.

Detection


Cosmic rays collide with the nuclei of atmospheric gases, producing a shower
Particle shower
In particle physics, a shower is a cascade of secondary particles produced as the result of a high-energy particle interacting with dense matter. The incoming particle interacts, producing multiple new particles with lesser energy; each of these then interacts in the same way, a process that...

 of, among others, pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....

s and kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...

s, that decay into muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...

s. These muons are able to reach the surface of the Earth, and even penetrate for some distance into shallow mines. Muons are easily detected by many types of particle detectors such as cloud chamber
Cloud chamber
The cloud chamber, also known as the Wilson chamber, is a particle detector used for detecting ionizing radiation. In its most basic form, a cloud chamber is a sealed environment containing a supersaturated vapor of water or alcohol. When a charged particle interacts with the mixture, it ionizes it...

s or bubble chamber
Bubble chamber
A bubble chamber is a vessel filled with a superheated transparent liquid used to detect electrically charged particles moving through it. It was invented in 1952 by Donald A. Glaser, for which he was awarded the 1960 Nobel Prize in Physics...

s or scintillation
Scintillation (physics)
Scintillation is a flash of light produced in a transparent material by an ionization event. See scintillator and scintillation counter for practical applications.-Overview:...

 detectors. Several muons observed by separated detectors at the same instant indicates that they have been produced in the same shower event.

Cosmic rays impacting other planetary bodies in the Solar System are detected indirectly by observing high energy gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...

 emissions by gamma-ray telescope. These are distinguished from radioactive decay processes by their higher energies above  about 10 MeV.

Detection by particle track-etch technique


Cosmic rays can also be detected directly by particle detectors aboard satellites or high altitude balloons. In a pioneering technique developed by Robert Fleischer, P. Buford Price
P. Buford Price
Paul Buford Price, usually known as P. Buford Price, is a professor in the Graduate School at the University of California, Berkeley and a member of the National Academy of Sciences...

, and Robert M. Walker, sheets of clear plastic, like 1/4 mil Lexan
Lexan
Lexan is a registered trademark for SABIC Innovative Plastics' brand of polycarbonate resin thermoplastic. Polycarbonate polymer is produced by reacting bisphenol A with carbonyl dichloride, also known as phosgene. Lexan is the brand name for polycarbonate sheet and resin in a wide range of grades...

 polycarbonate, are stacked together and exposed directly to cosmic rays in space or high altitude. The nuclear charge causes chemical bond breaking or ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 in the plastic. At the top of the plastic stack, the ionization is less due to the high cosmic ray speed. As the cosmic ray speed decreases due to deceleration in the stack, the ionization increases along the path. The resulting plastic sheets are "etched" or slowly dissolved in warm caustic sodium hydroxide solution, that removes the surface material at a slow, known rate. The caustic sodium hydroxide dissolves at a faster rate along the path of the ionized plastic. The net result is a conical shaped pit or etch pit in the plastic. The etch pits are measured under a high power microscope (typically 1600X oil-immersion), and the etch rate is plotted as a function of the depth in the stacked plastic. This yields a unique curve for each atomic nucleus of Z from 1 to 92, allowing identification of both the charge and energy of the cosmic ray that traverses the plastic stack. The more extensive the ionization along the path; the higher the charge.

This technique has been used with great success for detecting not only cosmic rays, but fission product nuclei for neutron detectors.

Detection by air shower


When cosmic rays enter the Earth's atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

 they collide with molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s, mainly oxygen and nitrogen, to produce a cascade of billions of lighter particles, a so-called air shower
Air shower (physics)
An air shower is an extensive cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray enters the atmosphere...

.

All of the produced particles stay within about one degree of the primary particle's path. Typical particles produced in such collisions are charged meson
Meson
In particle physics, mesons are subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometer: 10−15 m, which is about the size of a proton...

s e.g. positive and negative pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....

s and kaon
Kaon
In particle physics, a kaon is any one of a group of four mesons distinguished by the fact that they carry a quantum number called strangeness...

s. These subsequently decay into muons that are easily detected by many types of particle detectors.

Research and experiments


There are a number of cosmic ray research initiatives. These include, but are not limited to:

  • Ground Experiment
    • Akeno Giant Air Shower Array
    • CHICOS
      CHICOS
      The California High School Cosmic Ray Observatory, , operated by the Kellogg Laboratory at the California Institute of Technology in Pasadena, California, USA, is one of the world's largest ongoing Cosmic Ray observatory programs...

    • High Resolution Fly's Eye Cosmic Ray Detector
      High Resolution Fly's Eye Cosmic Ray Detector
      The High Resolution Fly's Eye or HiRes detector was an ultra-high-energy cosmic ray observatory that operated in the western Utah desert from May 1997 until April 2006. HiRes utilized the atmospheric fluorescence technique that was pioneered by the Utah group first in tests at the Volcano Ranch...

    • MAGIC
      MAGIC (telescope)
      MAGIC is a system of two Imaging Atmospheric Cherenkov telescopes situated at the Roque de los Muchachos Observatory on La Palma, one of the Canary Islands, at about 2200 m above sea level...

    • MARIACHI
      MARIACHI
      MARIACHI, the Mixed Apparatus for Radar Investigation of Cosmic-rays of High Ionization, is an apparatus for the detection of ultra-high-energy cosmic rays via bi-static radar using VHF transmitters. MARIACHI is also the name of the research project at Brookhaven National Laboratory operating the...

    • Pierre Auger Observatory
      Pierre Auger Observatory
      The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles with energies beyond 1020 eV...

    • Telescope Array Project
      Telescope Array Project
      The Telescope Array project is an international collaboration involving research and educational institutions in Japan, Taiwan, China, Russia, South Korea, and the United States. The experiment is designed to observe ultra-high-energy cosmic ray air showers using a combination of ground array and...

    • Washington Large Area Time Coincidence Array
      Washington Large Area Time Coincidence Array
      The Washington Area Large-scale Time-coincidence Array is a cosmic ray physics experiment run by the University of Washington to investigate ultra high energy cosmic rays . The program uses detectors placed at Seattle-area high schools and colleges which are linked via the internet, effectively...

    • CLOUD
      CLOUD
      Cosmics Leaving Outdoor Droplets or the CLOUD is an experimental facility being run at CERN by Jasper Kirkby to investigate the microphysics between galactic cosmic rays and aerosols under controlled conditions...

    • Spaceship Earth (detector)
      Spaceship Earth (detector)
      Spaceship Earth is a network of neutron monitors designed to measure the flux of cosmic rays arriving at Earth from different directions. All the 12 member neutron monitor stations are located at high latitude, which makes their detecting directions more precise, and their energy responses uniform...

    • Milagro
      Milagro (experiment)
      Milagro, , was a ground based water Čerenkov radiation telescope situated in the Jemez Mountains near Los Alamos, New Mexico at the Fenton Hill Observatory site. It was primarily designed to detect gamma rays but also detected large numbers of cosmic rays. It operated in the TeV region of the...

    • Real-time Neutron Monitor Database (NMDB)
    • KASCADE
      KASCADE
      KASCADE is a European physics experiment started in 1996 at Forschungszentrum Karlsruhe, Germany, an extensive air shower experiment array to study the cosmic ray primary composition and the hadronic interactions in the energy range of 1016–1018 eV, measuring simultaneously the electronic, muonic...

    • GAMMA
      GAMMA
      GAMMA experiment is a study of: a) Primary cosmic ray energy spectra and elemental composition at energies 1015-1018eV ;b) Galactic diffuse gamma-ray intensity at energies 1014-1015eV;...

    • GRAPES-3
      GRAPES-3
      GRAPES-3 is a project for cosmic ray study with air shower detector array and large area muon detectors at Ooty in southern India...

    • HEGRA
      HEGRA
      HEGRA, which stands for High-Energy-Gamma-Ray Astronomy, was an atmospheric Cherenkov telescope for Gamma-ray astronomy. With its various types of detectors, HEGRA took data between 1987 and 2002, at which point it was dismantled in order to build its successor, MAGIC, at the same site.It was...

    • Chicago Air Shower Array
      Chicago Air Shower Array
      The Chicago Air Shower Array was a very large array of scintillation counters located in Utah, fifty miles southwest of Salt Lake City in Dugway Proving Grounds. CASA began operating in 1992, in coincidence with a second array, the Michigan Anti , under the name CASA-MIA. The array was made of...

       (CASA)
    • IceCube

  • Satellite Experiment
    • PAMELA
    • Alpha Magnetic Spectrometer
      Alpha Magnetic Spectrometer
      The Alpha Magnetic Spectrometer, also designated AMS-02, is a particle physics experiment module that is mounted on the International Space Station. It is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments will help researchers study the formation of...

    • ACE (Advanced Composition Explorer)
      Advanced Composition Explorer
      Advanced Composition Explorer is a NASA space exploration mission being conducted as part of the Explorer program to study matter in situ, comprising energetic particles from the solar wind, the interplanetary medium, and other sources. Real-time data from ACE is used by the Space Weather...

    • Voyager 1
      Voyager 1
      The Voyager 1 spacecraft is a 722-kilogram space probe launched by NASA in 1977, to study the outer Solar System and eventually interstellar space. Operating for as of today , the spacecraft receives routine commands and transmits data back to the Deep Space Network. At a distance of as of...

       and Voyager 2
      Voyager 2
      The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

    • Cassini–Huygens
    • HEAO 1, Einstein Observatory(HEAO2)
      Einstein Observatory
      Einstein Observatory was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories...

      , HEAO 3
    • Fermi Gamma-ray Space Telescope
    • Solar and Heliospheric Observatory
      Solar and Heliospheric Observatory
      The Solar and Heliospheric Observatory is a spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on December 2, 1995 to study the Sun, and has discovered over 2100 comets. It began normal operations in May...

    • Interstellar Boundary Explorer
      Interstellar Boundary Explorer
      Interstellar Boundary Explorer is a NASA satellite that will make the first map of the boundary between the Solar System and interstellar space. The mission is part of NASA's Small Explorer program. The IBEX satellite was launched with a Pegasus-XL rocket on October 19, 2008, at 17:47:23 UTC...

    • Langton Ultimate Cosmic-Ray Intensity Detector
      LUCID
      LUCID, , is a cosmic ray detector being built for a satellite of Surrey Satellite Technology Ltd at the Simon Langton Grammar School for Boys, in Canterbury, England...




History


After the discovery of radioactivity
Radioactive decay
Radioactive decay is the process by which an atomic nucleus of an unstable atom loses energy by emitting ionizing particles . The emission is spontaneous, in that the atom decays without any physical interaction with another particle from outside the atom...

 by Henri Becquerel
Henri Becquerel
Antoine Henri Becquerel was a French physicist, Nobel laureate, and the discoverer of radioactivity along with Marie Curie and Pierre Curie, for which all three won the 1903 Nobel Prize in Physics.-Early life:...

 in 1896, it was generally believed that atmospheric electricity, ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 of the air
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

, was caused only by radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...

 from radioactive elements in the ground or the radioactive gases or isotopes of radon
Radon
Radon is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless noble gas, occurring naturally as the decay product of uranium or thorium. Its most stable isotope, 222Rn, has a half-life of 3.8 days...

 they produce. Measurements of ionization rates at increasing heights above the ground during the decade from 1900 to 1910 showed a decrease that could be explained as due to absorption of the ionizing radiation by the intervening air.

In 1909 Theodor Wulf
Theodor Wulf
Theodor Wulf was a German physicist and Jesuit priest who was one of the first experimenters to detect excess atmospheric radiation....

 developed an electrometer
Electrometer
An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical hand-made mechanical instruments to high-precision electronic devices...

, a device to measure the rate of ion production inside a hermetically sealed container, and used it to show higher levels of radiation at the top of the Eiffel Tower
Eiffel Tower
The Eiffel Tower is a puddle iron lattice tower located on the Champ de Mars in Paris. Built in 1889, it has become both a global icon of France and one of the most recognizable structures in the world...

 than at its base. However, his paper published in Physikalische Zeitschrift was not widely accepted. In 1911 Domenico Pacini
Domenico Pacini
Domenico Pacini was an Italian physicist noted for his contributions to the discovery of cosmic rays.-Biography:...

 observed simultaneous variations of the rate of ionization over a lake, over the sea, and at a depth of 3 meters from the surface. Pacini concluded from the decrease of radioactivity underwater that a certain part of the ionization must be due to sources other than the radioactivity of the Earth.

Then, in 1912, Victor Hess
Victor Francis Hess
Victor Francis Hess was an Austrian-American physicist, and Nobel laureate in physics, who discovered cosmic rays.-Early years:...

 carried three enhanced-accuracy Wulf electrometers to an altitude of 5300 meters in a free balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...

 flight. He found the ionization rate increased approximately fourfold over the rate at ground level. Hess also ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes. He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913–1914, Werner Kolhörster
Werner Kolhörster
Werner Heinrich Gustav Kolhörster was a German physicist and a pioneer of research into cosmic rays.Kolhörster was born in Schwiebus , Province of Brandenburg...

 confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km. Hess received the Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...

 in 1936 for his discovery.
The term "cosmic rays" was coined by Robert Millikan
Robert Millikan
Robert A. Millikan was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945...

 who confirmed in 1925 they were extraterrestrial in origin, and not produced by atmospheric electricity. Millikan believed that cosmic rays were high-energy photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...

s with some secondary electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s produced by Compton scattering
Compton scattering
In physics, Compton scattering is a type of scattering that X-rays and gamma rays undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy of an X-ray or gamma ray photon, called the Compton effect...

 of gamma rays. Compton himself held the (correct) belief that cosmic rays were primarily charged particles. During the decade from 1927 to 1937, a wide variety of experimental investigations demonstrated that the primary cosmic rays are mostly positively charged particles, and the secondary radiation observed at ground level is composed primarily of electrons, photons and muon
Muon
The muon |mu]] used to represent it) is an elementary particle similar to the electron, with a unitary negative electric charge and a spin of ½. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton...

s. In 1948, observations with nuclear emulsion
Nuclear emulsion
In a Particle and Nuclear physics, a nuclear emulsion plate is a photographic plate with a particularly thick emulsion layer and with a very uniform grain size. Like bubble chambers, cloud chambers, and wire chambers nuclear emulsion plates record the tracks of charged particles passing through...

s carried by balloons to near the top of the atmosphere by Gottlieb
Melvin B. Gottlieb
Melvin Burt Gottlieb was a high-energy physicist and director of the Princeton Plasma Physics Laboratory...

 and Van Allen
James Van Allen
James Alfred Van Allen was an American space scientist at the University of Iowa.The Van Allen radiation belts were named after him, following the 1958 satellite missions in which Van Allen had argued that a Geiger counter should be used to detect charged particles.- Life and career :* September...

 showed that the primary cosmic particles are mostly proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....

s with some helium nuclei (alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s) and a small fraction heavier nuclei.

In 1934, Bruno Rossi
Bruno Rossi
Bruno Benedetto Rossi was a leading Italian-American experimental physicist. He made major contributions to cosmic ray and particle physics from 1930 through the 1950s, and pioneered X-ray astronomy and space plasma physics in the 1960s.-Biography:Rossi was born in Venice, Italy...

 reported an observation of near-simultaneous discharges of two Geiger counter
Geiger counter
A Geiger counter, also called a Geiger–Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a...

s widely separated horizontally during a test of equipment he was using in a measurement of the so-called east-west effect. In his report on the experiment, Rossi wrote "...it seems that once in a while the recording equipment is struck by very extensive showers of particles, which causes coincidences between the counters, even placed at large distances from one another." In 1937 Pierre Auger
Pierre Victor Auger
Pierre Victor Auger was a French physicist, born in Paris. He worked in the fields of atomic physics, nuclear physics, and cosmic ray physics....

, unaware of Rossi's earlier report, detected the same phenomenon and investigated it in some detail. He concluded that extensive particle shower
Air shower (physics)
An air shower is an extensive cascade of ionized particles and electromagnetic radiation produced in the atmosphere when a primary cosmic ray enters the atmosphere...

s are generated by high-energy primary cosmic-ray particles that interact with air nuclei high in the atmosphere, initiating a cascade of secondary interactions that ultimately yield a shower of electrons, photons, and muons that reach ground level.

Attempts were made to measure the primary cosmic ray component at very high altitude. Soviet physicist Sergey Vernov was the first to use radiosonde
Radiosonde
A radiosonde is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. Radiosondes may operate at a radio frequency of 403 MHz or 1680 MHz and both types may be adjusted slightly higher or lower as required...

s to perform cosmic ray readings. On April 1, 1935, he took measurements at heights up to 13.6 kilometers using a pair of Geiger counter
Geiger counter
A Geiger counter, also called a Geiger–Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a...

s in an anti-coincidence circuit to avoid counting secondary ray showers.

Homi J. Bhabha
Homi J. Bhabha
Homi Jehangir Bhabha, FRS was an Indian nuclear physicist and the chief architect of the Indian atomic energy program...

 derived an expression for the probability of scattering positrons by electrons, a process now known as Bhabha scattering. His classic paper, jointly with Walter Heitler
Walter Heitler
Walter Heinrich Heitler was a German physicist who made contributions to quantum electrodynamics and quantum field theory...

, published in 1937 described how primary cosmic rays from space interact with the upper atmosphere to produce particles observed at the ground level. Bhabha and Heitler explained the cosmic ray shower formation by the cascade production of gamma rays and positive and negative electron pairs.

Measurements of the energy and arrival directions of the ultra-high energy primary cosmic rays by the techniques of "density sampling" and "fast timing" of extensive air showers were first carried out in 1954 by members of the Rossi Cosmic Ray Group at the Massachusetts Institute of Technology
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...

. The experiment employed eleven scintillation detectors
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...

 arranged within a circle 460 meters in diameter on the grounds of the Agassiz Station of the Harvard College Observatory
Harvard College Observatory
The Harvard College Observatory is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, USA, and was founded in 1839...

. From that work, and from many other experiments carried out all over the world, the energy spectrum of the primary cosmic rays is now known to extend beyond 1020 eV. A huge air shower experiment called the Auger Project
Pierre Auger Observatory
The Pierre Auger Observatory is an international cosmic ray observatory designed to detect ultra-high-energy cosmic rays: single sub-atomic particles with energies beyond 1020 eV...

 is currently operated at a site on the pampa
Pampa
The Pampas are the fertile South American lowlands, covering more than , that include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos and Córdoba, most of Uruguay, and the southernmost Brazilian State, Rio Grande do Sul...

s of Argentina by an international consortium of physicists, led by James Cronin
James Cronin
James Watson Cronin is an American nuclear physicist.Cronin was born in Chicago, Illinois and attended Southern Methodist University in Dallas, Texas. Cronin and co-researcher Val Logsdon Fitch were awarded the 1980 Nobel Prize in Physics for a 1964 experiment that proved that certain subatomic...

, 1980 Nobel Prize in Physics
Nobel Prize in Physics
The Nobel Prize in Physics is awarded once a year by the Royal Swedish Academy of Sciences. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895 and awarded since 1901; the others are the Nobel Prize in Chemistry, Nobel Prize in Literature, Nobel Peace Prize, and...

 of the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...

 and Alan Watson of the University of Leeds
University of Leeds
The University of Leeds is a British Redbrick university located in the city of Leeds, West Yorkshire, England...

. Their aim is to explore the properties and arrival directions of the very highest energy primary cosmic rays. The results are expected to have important implications for particle physics and cosmology, due to a theoretical Greisen–Zatsepin–Kuzmin limit
Greisen–Zatsepin–Kuzmin limit
The Greisen–Zatsepin–Kuzmin limit is a theoretical upper limit on the energy of cosmic rays coming from "distant" sources. The limit is 5×1019 eV, or about 8 joules. The limit is set by slowing-interactions of cosmic ray protons with the microwave background radiation over long distances...

 to the energies of cosmic rays from long distances (about 160 million light years) which occurs above 1020 eV.

In November, 2007 preliminary results were announced showing direction of origination of the 27 highest energy events were strongly correlated with the locations of active galactic nuclei
Active galactic nucleus
An active galactic nucleus is a compact region at the centre of a galaxy that has a much higher than normal luminosity over at least some portion, and possibly all, of the electromagnetic spectrum. Such excess emission has been observed in the radio, infrared, optical, ultra-violet, X-ray and...

 [AGN], where bare protons are believed accelerated by strong magnetic fields associated with the large black hole
Black hole
A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

s at the AGN centers to energies of 1020 eV and higher.

Changes in atmospheric chemistry


Cosmic rays ionize the nitrogen and oxygen molecules in the atmosphere, which leads to a number of chemical reactions. One of the reactions results in ozone depletion. The magnitude of damage, however, is very small compared to the depletion caused by CFCs. Cosmic rays are also responsible for the continuous production of a number of unstable isotopes
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...

 in the Earth’s atmosphere, such as carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

, via the reaction:



Cosmic rays kept the level of carbon-14
Carbon-14
Carbon-14, 14C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues , to date archaeological, geological, and hydrogeological...

  in the atmosphere roughly constant (70 tons) for at least the past 100,000 years, until the beginning of above-ground nuclear weapons testing in the early 1950s. This is an important fact used in radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

 used in archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

.

Reaction products of primary cosmic rays, lifetime and reaction

Role in ambient radiation


Cosmic rays constitute a fraction of the annual radiation exposure of human beings on the Earth. For example, the average annual radiation exposure in Australia is 0.3 mSv
Sievert
The sievert is the International System of Units SI derived unit of dose equivalent radiation. It attempts to quantitatively evaluate the biological effects of ionizing radiation as opposed to just the absorbed dose of radiation energy, which is measured in gray...

 due to cosmic rays, out of a total of 2.3 mSv.

Effect on electronics


Cosmic rays have sufficient energy to alter the states of elements in electronic
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

s, causing transient errors to occur, such as corrupted data in electronic memory devices, or incorrect performance of CPUs, often referred to as "soft error
Soft error
In electronics and computing, a soft error is an error in a signal or datum which is wrong. Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component. A soft error is also a signal or datum which is wrong, but is not assumed to...

s" (not to be confused with software errors caused by programming mistakes/bugs). This has been a problem in extremely high-altitude electronics
Electronics
Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

, such as in satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

s, but with transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s becoming smaller and smaller, this is becoming an increasing concern in ground-level electronics as well. Studies by IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

 in the 1990s suggest that computers typically experience about one cosmic-ray-induced error per 256 megabytes of RAM
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...

 per month.

To alleviate this problem, the Intel Corporation
Intel Corporation
Intel Corporation is an American multinational semiconductor chip maker corporation headquartered in Santa Clara, California, United States and the world's largest semiconductor chip maker, based on revenue. It is the inventor of the x86 series of microprocessors, the processors found in most...

 has proposed a cosmic ray detector that could be integrated into future high-density microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

s, allowing the processor to repeat the last command following a cosmic-ray event.

Cosmic rays are suspected as a possible cause of an in-flight incident in 2008 where an Airbus A330
Airbus A330
The Airbus A330 is a wide-body twin-engine jet airliner made by Airbus, a division of EADS. Versions of the A330 have a range of and can accommodate up to 335 passengers in a two-class layout or carry of cargo....

 airliner of Qantas
Qantas
Qantas Airways Limited is the flag carrier of Australia. The name was originally "QANTAS", an initialism for "Queensland and Northern Territory Aerial Services". Nicknamed "The Flying Kangaroo", the airline is based in Sydney, with its main hub at Sydney Airport...

 twice plunged hundreds of feet
Qantas Flight 72
Qantas Flight 72 was a scheduled flight from Singapore Changi Airport to Perth Airport on 7 October 2008 that made an emergency landing at Learmonth airport near the town of Exmouth, Western Australia following an inflight accident featuring a pair of sudden uncommanded pitch-down manoeuvres that...

 after an unexplained malfunction in its flight control system. Many passengers and crew members were injured, some seriously. After this incident, the accident investigators determined that the airliner's flight control system had received a data spike that could not be explained, and that all systems were in perfect working order. This has prompted a software upgrade to all A330 and A340 airliners, worldwide, so that any data spikes in this system are filtered out electronically.

Significance to space travel



Galactic cosmic ray
Galactic cosmic ray
Galactic cosmic rays are cosmic rays that have their origin inside our Galaxy. GCRs are high-energy charged particles, and are usually protons, electrons, and fully ionized nuclei of light elements...

s are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.
Cosmic Rays also place a threat to electronics placed aboard outgoing probes. In 2010, a malfunction aboard the Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

 space probe was credited to a single flipped bit, probably caused by a cosmic ray.

Role in lightning


Cosmic rays have been implicated in the triggering of electrical breakdown in lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...

. It has been proposed that essentially all lightning is triggered through a relativistic process, "runaway breakdown
Runaway breakdown
Runaway breakdown is a theory of lightning initiation proposed by Alex Gurevich in 1992.Electrons in air have a mean free path of ~1cm. Fast electrons which move at a large fraction of the speed of light have a mean free path up to 100 times longer...

", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.

Role in climate change


A role of cosmic rays directly or via solar-induced modulations in climate change was suggested by E.P.Ney in 1959 and by Robert Dickinson in 1975. In recent years, the idea has been revived most notably by Henrik Svensmark
Henrik Svensmark
Henrik Svensmark is a physicist at the Danish National Space Center in Copenhagen who studies the effects of cosmic rays on cloud formation. His work presents hypotheses about solar activity as an indirect cause of global warming; his research has suggested a possible link through the interaction...

; the most recent IPCC study disputed the mechanism, while the most comprehensive review of the topic to date states: "evidence for the cosmic ray forcing is increasing as is the understanding of its physical principles."

Suggested mechanisms


Henrik Svensmark
Henrik Svensmark
Henrik Svensmark is a physicist at the Danish National Space Center in Copenhagen who studies the effects of cosmic rays on cloud formation. His work presents hypotheses about solar activity as an indirect cause of global warming; his research has suggested a possible link through the interaction...

 et al. have argued that solar variations modulate the cosmic ray signal seen at the Earth and that this would affect cloud formation and hence climate. Cosmic rays have been experimentally determined capable of producing ultra-small aerosol particles, orders of magnitude smaller than cloud condensation nuclei
Cloud condensation nuclei
Cloud condensation nuclei or CCNs are small particles typically 0.2 µm, or 1/100 th the size of a cloud droplet ) about which cloud droplets coalesce. Water requires a non-gaseous surface to make the transition from a vapour to a liquid. In the atmosphere, this surface presents itself as tiny...

 (CCN).

According to a report about an ongoing CERN CLOUD
CLOUD
Cosmics Leaving Outdoor Droplets or the CLOUD is an experimental facility being run at CERN by Jasper Kirkby to investigate the microphysics between galactic cosmic rays and aerosols under controlled conditions...

 research project to detect any Cosmic ray forcing is challenging since on wide spread time scales changes in the Sun’s magnetic activity, Earth’s magnetic field, and the galactic environment must be taken into account. Empirically, increased galactic cosmic ray (GCR) flux seem to be associated with a cooler climate, a southerly shift of the ITCZ (Inter Tropical Convergence Zone) and a weakening of monsoon rainfalls and vice versa. Claims have been made of identification of GCR climate signals in atmospheric parameters such as high latitude precipitation (Todd & Kniveton), and Svensmark's annual cloud cover variations, which were said to be correlated to GCR variation. Various proposals have been made for the mechanism by which cosmic rays might affect clouds, including ion mediated nucleation, and indirect effects on current flow density in the global electric circuit (see Tinsley 2000, and F. Yu 1999).... Other studies refer to the formation of relatively highly charged aerosols and cloud droplets at cloud boundaries, with an indirect effect on ice particle formation and altering aerosol interaction with cloud droplets.
Kirkby (2009) reviews developments and describes further cloud nucleation mechanisms that appear energetically favorable and depend on GCRs.,

Geochemical and astrophysical evidence



Nir Shaviv
Nir Shaviv
Nir Joseph Shaviv is an Israeli/American physics professor, carrying out research in the fields of astrophysics and climate science. He is currently an associate professor at the Racah Institute of Physics of the Hebrew University of Jerusalem....

 has argued that climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 signals on geological time scales are attributable to changing positions of the galactic spiral arms of the Milky Way Galaxy, and that cosmic ray flux variability is the dominant "climate driver" over these time periods. Nir Shaviv and Jan Veizer
Jan Veizer
Ján Veizer is the Distinguished University Professor of Earth Sciences at the University of Ottawa and Institute for Geology, Mineralogy und Geophysis, of Bochum Ruhr University, he held the NSERC/Noranda/CIFAR Industrial Chair in Earth System Isotope and Environmental Geochemistry until 2004...

 in 2003 argue, that in contrast to a carbon based scenario, the model and proxy based estimates of atmospheric CO2 levels especially for the early Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...

 (see diagrams) do not show correlation with the paleoclimate picture that emerged from geological criteria, while cosmic ray flux would do.

The 2007 IPCC reports, however, strongly attribute a major role of anthropogenic carbon dioxide in the ongoing global warming, but as "different climate changes in the past had different causes" a driving role of carbon dioxide in the geological past is neither focus of the IPCC nor purported. Similarly, according a BBC report a 2008 Lancaster University
Lancaster University
Lancaster University, officially The University of Lancaster, is a leading research-intensive British university in Lancaster, Lancashire, England. The university was established by Royal Charter in 1964 and initially based in St Leonard's Gate until moving to a purpose-built 300 acre campus at...

 study produced "further compelling evidence showing that modern-day climate change is not caused by changes in the Sun's activity".

A comprehensive study of different research institutes was published 2007 by Scherer et al. in Space Science Reviews 2007. The study combines geochemical evidence both on temperature, cosmic rays influence and as well astrophysical deliberations suggesting a major role in climate variability over different geological time scales. Proxy data of CRF influence comprise among others isotopic evidence in sediments on the Earth and as well changes in (iron) meteorites.

See also

  • Environmental radioactivity
    Environmental radioactivity
    Environmental radioactivity is produced by radioactive materials in the human environment. While some radioisotopes, such as strontium-90 and technetium-99 , are only found on Earth as a result of human activity, and some, like potassium-40 , are only present due to natural processes, a few...

  • Cosmic ray spallation
    Cosmic ray spallation
    Cosmic ray spallation is a form of naturally occurring nuclear fission and nucleosynthesis. It refers to the formation of elements from the impact of cosmic rays on an object. Cosmic rays are highly energetic charged particles from outside of Earth ranging from protons, alpha particles, and nuclei...

  • Forbush decrease
    Forbush decrease
    A Forbush decrease is a rapid decrease in the observed galactic cosmic ray intensity following a coronal mass ejection . It occurs due to the magnetic field of the plasma solar wind sweeping some of the galactic cosmic rays away from Earth. The term Forbush decrease was named after the American...

  • Gilbert Jerome Perlow
    Gilbert Jerome Perlow
    Gilbert "Gil" Jerome Perlow , was an American physicist famous for his work related to the Mössbauer effect, and an editor of the Journal of Applied Physics and Applied Physics Letters.- Life :...

  • Ultra-high-energy cosmic ray
    Ultra-high-energy cosmic ray
    In astroparticle physics, an ultra-high-energy cosmic ray or extreme-energy cosmic ray is a cosmic ray with an extreme kinetic energy, far beyond both its rest mass and energies typical of other cosmic rays....

  • Galactic cosmic ray
    Galactic cosmic ray
    Galactic cosmic rays are cosmic rays that have their origin inside our Galaxy. GCRs are high-energy charged particles, and are usually protons, electrons, and fully ionized nuclei of light elements...

  • Extragalactic cosmic ray
    Extragalactic cosmic ray
    Extragalactic cosmic rays are very-high-energy particles that flow into our solar system from beyond our galaxy. The energies these particles possess are in excess of 1015 eV.- Origin :...

  • Solar energetic particle
  • Track Imaging Cherenkov Experiment
    Track Imaging Cherenkov Experiment
    The Track Imaging Cherenkov Experiment is a ground-based cosmic ray telescope located at Argonne National Laboratory near Chicago, IL. The telescope, which contains a Fresnel lens, eight spherical mirrors, and a camera with 16 multianode photomultiplier tubes, uses the atmospheric Cherenkov...


External links