Van Allen radiation belt

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This CGI video illustrates changes in the shape and intensity of a cross section of the Van Allen belts.
A cross section of Van Allen radiation belts Van Allen radiation belt.svg
A cross section of Van Allen radiation belts

Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetosphere. Earth has two such belts, and sometimes others may be temporarily created. The belts are named after James Van Allen, who is often credited with their discovery. [1]

Contents

Earth's two main belts extend from an altitude of about 640 to 58,000 km (400 to 36,040 mi) [2] above the surface, in which region radiation levels vary. The belts are in the inner region of Earth's magnetic field. They trap energetic electrons and protons. Other nuclei, such as alpha particles, are less prevalent. Most of the particles that form the belts are thought to come from the solar wind while others arrive as cosmic rays. [3] By trapping the solar wind, the magnetic field deflects those energetic particles and protects the atmosphere from destruction.

The belts endanger satellites, which must have their sensitive components protected with adequate shielding if they spend significant time near that zone. Apollo Astronauts going through the Van Allen Belts received a very low and harmless dose of radiation. [4] [5]

In 2013, the Van Allen Probes detected a transient, third radiation belt, which persisted for four weeks. [6]

Discovery

Kristian Birkeland, Carl Størmer, Nicholas Christofilos, and Enrico Medi had investigated the possibility of trapped charged particles before the Space Age. [7] The second Soviet satellite Sputnik 2 which had detectors designed by Sergei Vernov, [8] followed by the US satellites Explorer 1 and Explorer 3, [9] confirmed the existence of the belt in early 1958, later named after James Van Allen from the University of Iowa. [1] The trapped radiation was first mapped by Explorer 4, Pioneer 3, and Luna 1.

The term Van Allen belts refers specifically to the radiation belts surrounding Earth; however, similar radiation belts have been discovered around other planets. The Sun does not support long-term radiation belts, as it lacks a stable, global dipole field. The Earth's atmosphere limits the belts' particles to regions above 200–1,000 km, [10] (124–620 miles) while the belts do not extend past 8 Earth radii RE. [10] The belts are confined to a volume which extends about 65° [10] on either side of the celestial equator.

Research

Jupiter's variable radiation belts Jupiter radio.jpg
Jupiter's variable radiation belts

The NASA Van Allen Probes mission aims at understanding (to the point of predictability) how populations of relativistic electrons and ions in space form or change in response to changes in solar activity and the solar wind. NASA Institute for Advanced Concepts–funded studies have proposed magnetic scoops to collect antimatter that naturally occurs in the Van Allen belts of Earth, although only about 10 micrograms of antiprotons are estimated to exist in the entire belt. [11]

The Van Allen Probes mission successfully launched on August 30, 2012. The primary mission was scheduled to last two years with expendables expected to last four. The probes were deactivated in 2019 after running out of fuel and are expected to deorbit during the 2030s. [12] NASA's Goddard Space Flight Center manages the Living With a Star program—of which the Van Allen Probes were a project, along with Solar Dynamics Observatory (SDO). The Applied Physics Laboratory was responsible for the implementation and instrument management for the Van Allen Probes. [13]

Radiation belts exist around other planets and moons in the solar system that have magnetic fields powerful enough to sustain them. To date, most of these radiation belts have been poorly mapped. The Voyager Program (namely Voyager 2) only nominally confirmed the existence of similar belts around Uranus and Neptune.

Geomagnetic storms can cause electron density to increase or decrease relatively quickly (i.e., approximately one day or less). Longer-timescale processes determine the overall configuration of the belts. After electron injection increases electron density, electron density is often observed to decay exponentially. Those decay time constants are called "lifetimes." Measurements from the Van Allen Probe B's Magnetic Electron Ion Spectrometer (MagEIS) show long electron lifetimes (i.e., longer than 100 days) in the inner belt; short electron lifetimes of around one or two days are observed in the "slot" between the belts; and energy-dependent electron lifetimes of roughly five to 20 days are found in the outer belt. [14]

Inner belt

Cutaway drawing of two radiation belts around Earth: the inner belt (red) dominated by protons and the outer one (blue) by electrons. Image Credit: NASA Rendering of Van Allen radiation belts of Earth 2.jpg
Cutaway drawing of two radiation belts around Earth: the inner belt (red) dominated by protons and the outer one (blue) by electrons. Image Credit: NASA

The inner Van Allen Belt extends typically from an altitude of 0.2 to 2 Earth radii (L values of 1.2 to 3) or 1,000 km (620 mi) to 12,000 km (7,500 mi) above the Earth. [3] [15] In certain cases, when solar activity is stronger or in geographical areas such as the South Atlantic Anomaly, the inner boundary may decline to roughly 200 km [16] above the Earth's surface. The inner belt contains high concentrations of electrons in the range of hundreds of keV and energetic protons with energies exceeding 100 MeV—trapped by the relatively strong magnetic fields in the region (as compared to the outer belt). [17]

It is thought that proton energies exceeding 50 MeV in the lower belts at lower altitudes are the result of the beta decay of neutrons created by cosmic ray collisions with nuclei of the upper atmosphere. The source of lower energy protons is believed to be proton diffusion, due to changes in the magnetic field during geomagnetic storms. [18]

Due to the slight offset of the belts from Earth's geometric center, the inner Van Allen belt makes its closest approach to the surface at the South Atlantic Anomaly. [19] [20]

In March 2014, a pattern resembling "zebra stripes" was observed in the radiation belts by the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) onboard Van Allen Probes. The initial theory proposed in 2014 was that—due to the tilt in Earth's magnetic field axis—the planet's rotation generated an oscillating, weak electric field that permeates through the entire inner radiation belt. [21] A 2016 study instead concluded that the zebra stripes were an imprint of ionospheric winds on radiation belts. [22]

Outer belt

Laboratory simulation of the Van Allen belt's influence on the Solar Wind; these aurora-like Birkeland currents were created by the scientist Kristian Birkeland in his terrella, a magnetized anode globe in an evacuated chamber Birkeland-anode-globe-fig259.jpg
Laboratory simulation of the Van Allen belt's influence on the Solar Wind; these aurora-like Birkeland currents were created by the scientist Kristian Birkeland in his terrella, a magnetized anode globe in an evacuated chamber

The outer belt consists mainly of high-energy (0.1–10  MeV) electrons trapped by the Earth's magnetosphere. It is more variable than the inner belt, as it is more easily influenced by solar activity. It is almost toroidal in shape, beginning at an altitude of 3 Earth radii and extending to 10 Earth radii (RE)—13,000 to 60,000 kilometres (8,100 to 37,300 mi) above the Earth's surface.[ citation needed ] Its greatest intensity is usually around 4 to 5 RE. The outer electron radiation belt is mostly produced by inward radial diffusion [23] [24] and local acceleration [25] due to transfer of energy from whistler-mode plasma waves to radiation belt electrons. Radiation belt electrons are also constantly removed by collisions with Earth's atmosphere, [25] losses to the magnetopause, and their outward radial diffusion. The gyroradii of energetic protons would be large enough to bring them into contact with the Earth's atmosphere. Within this belt, the electrons have a high flux and at the outer edge (close to the magnetopause), where geomagnetic field lines open into the geomagnetic "tail", the flux of energetic electrons can drop to the low interplanetary levels within about 100 km (62 mi)—a decrease by a factor of 1,000.

In 2014, it was discovered that the inner edge of the outer belt is characterized by a very sharp transition, below which highly relativistic electrons (> 5MeV) cannot penetrate. [26] The reason for this shield-like behavior is not well understood.

The trapped particle population of the outer belt is varied, containing electrons and various ions. Most of the ions are in the form of energetic protons, but a certain percentage are alpha particles and O+ oxygen ions—similar to those in the ionosphere but much more energetic. This mixture of ions suggests that ring current particles probably originate from more than one source.

The outer belt is larger than the inner belt, and its particle population fluctuates widely. Energetic (radiation) particle fluxes can increase and decrease dramatically in response to geomagnetic storms, which are themselves triggered by magnetic field and plasma disturbances produced by the Sun. The increases are due to storm-related injections and acceleration of particles from the tail of the magnetosphere. Another cause of variability of the outer belt particle populations is the wave-particle interactions with various plasma waves in a broad range of frequencies. [27]

On February 28, 2013, a third radiation belt—consisting of high-energy ultrarelativistic charged particles—was reported to be discovered. In a news conference by NASA's Van Allen Probe team, it was stated that this third belt is a product of coronal mass ejection from the Sun. It has been represented as a separate creation which splits the Outer Belt, like a knife, on its outer side, and exists separately as a storage container of particles for a month's time, before merging once again with the Outer Belt. [28]

The unusual stability of this third, transient belt has been explained as due to a 'trapping' by the Earth's magnetic field of ultrarelativistic particles as they are lost from the second, traditional outer belt. While the outer zone, which forms and disappears over a day, is highly variable due to interactions with the atmosphere, the ultrarelativistic particles of the third belt are thought not to scatter into the atmosphere, as they are too energetic to interact with atmospheric waves at low latitudes. [29] This absence of scattering and the trapping allows them to persist for a long time, finally only being destroyed by an unusual event, such as the shock wave from the Sun.

Flux values

In the belts, at a given point, the flux of particles of a given energy decreases sharply with energy.

At the magnetic equator, electrons of energies exceeding 5000 keV (resp. 5 MeV) have omnidirectional fluxes ranging from 1.2×106 (resp. 3.7×104) up to 9.4×109 (resp. 2×107) particles per square centimeter per second.

The proton belts contain protons with kinetic energies ranging from about 100 keV, which can penetrate 0.6 μm of lead, to over 400 MeV, which can penetrate 143 mm of lead. [30]

Most published flux values for the inner and outer belts may not show the maximum probable flux densities that are possible in the belts. There is a reason for this discrepancy: the flux density and the location of the peak flux is variable, depending primarily on solar activity, and the number of spacecraft with instruments observing the belt in real time has been limited. The Earth has not experienced a solar storm of Carrington event intensity and duration, while spacecraft with the proper instruments have been available to observe the event.

Radiation levels in the belts would be dangerous to humans if they were exposed for an extended period of time. The Apollo missions minimised hazards for astronauts by sending spacecraft at high speeds through the thinner areas of the upper belts, bypassing inner belts completely, except for the Apollo 14 mission where the spacecraft traveled through the heart of the trapped radiation belts. [19] [31] [4] [32]

Antimatter confinement

In 2011, a study confirmed earlier speculation that the Van Allen belt could confine antiparticles. The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment detected levels of antiprotons orders of magnitude higher than are expected from normal particle decays while passing through the South Atlantic Anomaly. This suggests the Van Allen belts confine a significant flux of antiprotons produced by the interaction of the Earth's upper atmosphere with cosmic rays. [33] The energy of the antiprotons has been measured in the range from 60 to 750 MeV.

Research funded by the NASA Institute for Advanced Concepts concluded that harnessing these antiprotons for spacecraft propulsion would be feasible. Researchers believed that this approach would have advantages over antiproton generation at CERN because collecting the particles in situ eliminates transportation losses and costs. Jupiter and Saturn are also possible sources, but the Earth belt is the most productive. Jupiter is less productive than might be expected due to magnetic shielding from cosmic rays of much of its atmosphere. In 2019, CMS announced that the construction of a device that would be capable of collecting these particles has already begun.[ dubious – discuss ] NASA will use this device to collect these particles and transport them to institutes all around the world for further examination. These so-called "antimatter containers" could be used for industrial purposes as well in the future. [34]

Implications for space travel

Orbit size comparison of GPS, GLONASS, Galileo, BeiDou-2, and Iridium constellations, the International Space Station, the Hubble Space Telescope, and geostationary orbit (and its graveyard orbit), with the Van Allen radiation belts and the Earth to scale. The Moon's orbit is around 9 times as large as geostationary orbit. (In the SVG file, hover over an orbit or its label to highlight it; click to load its article.) Comparison satellite navigation orbits.svg
Orbit size comparison of GPS, GLONASS, Galileo, BeiDou-2, and Iridium constellations, the International Space Station, the Hubble Space Telescope, and geostationary orbit (and its graveyard orbit), with the Van Allen radiation belts and the Earth to scale.
The Moon's orbit is around 9 times as large as geostationary orbit. (In the SVG file, hover over an orbit or its label to highlight it; click to load its article.)

Spacecraft travelling beyond low Earth orbit enter the zone of radiation of the Van Allen belts. Beyond the belts, they face additional hazards from cosmic rays and solar particle events. A region between the inner and outer Van Allen belts lies at 2 to 4 Earth radii and is sometimes referred to as the "safe zone". [35] [36]

Solar cells, integrated circuits, and sensors can be damaged by radiation. Geomagnetic storms occasionally damage electronic components on spacecraft. Miniaturization and digitization of electronics and logic circuits have made satellites more vulnerable to radiation, as the total electric charge in these circuits is now small enough so as to be comparable with the charge of incoming ions. Electronics on satellites must be hardened against radiation to operate reliably. The Hubble Space Telescope, among other satellites, often has its sensors turned off when passing through regions of intense radiation. [37] A satellite shielded by 3 mm of aluminium in an elliptic orbit (200 by 20,000 miles (320 by 32,190 km)) passing the radiation belts will receive about 2,500 rem (25  Sv) per year. (For comparison, a full-body dose of 5 Sv is deadly.) Almost all radiation will be received while passing the inner belt. [38]

The Apollo missions marked the first event where humans traveled through the Van Allen belts, which was one of several radiation hazards known by mission planners. [39] The astronauts had low exposure in the Van Allen belts due to the short period of time spent flying through them. [4] [5]

Astronauts' overall exposure was actually dominated by solar particles once outside Earth's magnetic field. The total radiation received by the astronauts varied from mission-to-mission but was measured to be between 0.16 and 1.14 rads (1.6 and 11.4  mGy), much less than the standard of 5 rem (50 mSv) [lower-alpha 3] per year set by the United States Atomic Energy Commission for people who work with radioactivity. [39]

Causes

It is generally understood that the inner and outer Van Allen belts result from different processes. The inner belt is mainly composed of energetic protons produced from the decay of so-called "albedo" neutrons, which are themselves the result of cosmic ray collisions in the upper atmosphere. The outer Van Allen belt consists mainly of electrons. They are injected from the geomagnetic tail following geomagnetic storms, and are subsequently energized through wave-particle interactions.

In the inner belt, particles that originate from the Sun are trapped in the Earth's magnetic field. Particles spiral along the magnetic lines of flux as they move "latitudinally" along those lines. As particles move toward the poles, the magnetic field line density increases, and their "latitudinal" velocity is slowed and can be reversed, deflecting the particles back towards the equatorial region, causing them to bounce back and forth between the Earth's poles. [40] In addition to both spiralling around and moving along the flux lines, the electrons drift slowly in an eastward direction, while the protons drift westward.

The gap between the inner and outer Van Allen belts is sometimes called the "safe zone" or "safe slot", and is the location of medium Earth orbits. The gap is caused by the VLF radio waves, which scatter particles in pitch angle, which adds new ions to the atmosphere. Solar outbursts can also dump particles into the gap, but those drain out in a matter of days. The VLF radio waves were previously thought to be generated by turbulence in the radiation belts, but recent work by J.L. Green of the Goddard Space Flight Center [ citation needed ] compared maps of lightning activity collected by the Microlab 1 spacecraft with data on radio waves in the radiation-belt gap from the IMAGE spacecraft; the results suggest that the radio waves are actually generated by lightning within Earth's atmosphere. The generated radio waves strike the ionosphere at the correct angle to pass through only at high latitudes, where the lower ends of the gap approach the upper atmosphere. These results are still being debated in the scientific community.

Proposed removal

Draining the charged particles from the Van Allen belts would open up new orbits for satellites and make travel safer for astronauts. [41]

High Voltage Orbiting Long Tether, or HiVOLT, is a concept proposed by Russian physicist V. V. Danilov and further refined by Robert P. Hoyt and Robert L. Forward for draining and removing the radiation fields of the Van Allen radiation belts [42] that surround the Earth. [43]

Another proposal for draining the Van Allen belts involves beaming very-low-frequency (VLF) radio waves from the ground into the Van Allen belts. [44]

Draining radiation belts around other planets has also been proposed, for example, before exploring Europa, which orbits within Jupiter's radiation belt. [45]

As of 2014, it remains uncertain if there are any negative unintended consequences to removing these radiation belts. [41]

See also

Explanatory notes

  1. ↑ Orbital periods and speeds are calculated using the relations 4π2R3 = T2GM and V2R = GM, where R is the radius of orbit in metres; T is the orbital period in seconds; V is the orbital speed in m/s; G is the gravitational constant, approximately 6.673×10−11 Nm2/kg2; M is the mass of Earth, approximately 5.98×1024 kg (1.318×1025 lb).
  2. ↑ Approximately 8.6 times (in radius and length) when the Moon is nearest (that is, 363,104 km/42,164 km), to 9.6 times when the Moon is farthest (that is, 405,696 km/42,164 km).
  3. ↑ For beta, gamma, and x-rays the absorbed dose in rads equals the dose equivalent in rem

Citations

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  10. 1 2 3 Walt, Martin (2005) [Originally published 1994]. Introduction to Geomagnetically Trapped Radiation. Cambridge; New York: Cambridge University Press. ISBN   978-0-521-61611-9. LCCN   2006272610. OCLC   63270281.
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  19. 1 2 "The Van Allen Belts". NASA/GSFC. Archived from the original on 2019-12-20. Retrieved 2011-05-25.
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  22. ↑ Lejosne, S.; Roederer, J.G. (2016). "The "zebra stripes": An effect of F region zonal plasma drifts on the longitudinal distribution of radiation belt particles". Journal of Geophysical Research . 121 (1): 507–518. Bibcode:2016JGRA..121..507L. doi: 10.1002/2015JA021925 .
  23. ↑ Elkington, S. R.; Hudson, M. K.; Chan, A. A. (May 2001). "Enhanced Radial Diffusion of Outer Zone Electrons in an Asymmetric Geomagnetic Field". Spring Meeting 2001. Washington, D.C.: American Geophysical Union. Bibcode:2001AGUSM..SM32C04E.
  24. ↑ Shprits, Y. Y.; Thorne, R. M. (2004). "Time dependent radial diffusion modeling of relativistic electrons with realistic loss rates". Geophysical Research Letters . 31 (8): L08805. Bibcode:2004GeoRL..31.8805S. doi: 10.1029/2004GL019591 .
  25. 1 2 Horne, Richard B.; Thorne, Richard M.; Shprits, Yuri Y.; et al. (2005). "Wave acceleration of electrons in the Van Allen radiation belts". Nature . 437 (7056): 227–230. Bibcode:2005Natur.437..227H. doi:10.1038/nature03939. PMID   16148927. S2CID   1530882.
  26. ↑ D. N. Baker; A. N. Jaynes; V. C. Hoxie; R. M. Thorne; J. C. Foster; X. Li; J. F. Fennell; J. R. Wygant; S. G. Kanekal; P. J. Erickson; W. Kurth; W. Li; Q. Ma; Q. Schiller; L. Blum; D. M. Malaspina; A. Gerrard & L. J. Lanzerotti (27 November 2014). "An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts". Nature. 515 (7528): 531–534. Bibcode:2014Natur.515..531B. doi:10.1038/nature13956. PMID   25428500. S2CID   205241480.
  27. ↑ Pokhotelov, D.; Lefeuvre, F.; Horne, R.B.; Cornilleau-Wehrlin, N. (2008). "Survey of ELF-VLF plasma waves in the outer radiation belt observed by Cluster STAFF-SA experiment". Annales Geophysicae. 26 (11): 3269–3277. Bibcode:2008AnGeo..26.3269P. doi: 10.5194/angeo-26-3269-2008 . S2CID   122756498.
  28. ↑ NASA's Van Allen Probes Discover Third Radiation Belt Around Earth on YouTube
  29. ↑ Shprits, Yuri Y.; Subbotin, Dimitriy; Drozdov, Alexander; et al. (2013). "Unusual stable trapping of the ultrarelativistic electrons in the Van Allen radiation belts". Nature Physics . 9 (11): 699–703. Bibcode:2013NatPh...9..699S. doi: 10.1038/nphys2760 .
  30. ↑ Hess, Wilmot N. (1968). The Radiation Belt and Magnetosphere. Waltham, MA: Blaisdell Pub. Co. LCCN   67019536. OCLC   712421.
  31. ↑ Modisette, Jerry L.; Lopez, Manuel D.; Snyder, Joseph W. (January 20–22, 1969). Radiation Plan for the Apollo Lunar Mission. AIAA 7th Aerospace Sciences Meeting. New York. doi:10.2514/6.1969-19. AIAA Paper No. 69-19.
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  39. 1 2 Bailey, J. Vernon. "Radiation Protection and Instrumentation". Biomedical Results of Apollo. Retrieved 2011-06-13.
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  41. 1 2 Charles Q. Choi. "Hacking the Van Allen Belts". 2014.
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A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere caused by a solar wind shock wave.

<span class="mw-page-title-main">Magnetosphere of Saturn</span> Cavity in the solar wind the sixth planet creates

The magnetosphere of Saturn is the cavity created in the flow of the solar wind by the planet's internally generated magnetic field. Discovered in 1979 by the Pioneer 11 spacecraft, Saturn's magnetosphere is the second largest of any planet in the Solar System after Jupiter. The magnetopause, the boundary between Saturn's magnetosphere and the solar wind, is located at a distance of about 20 Saturn radii from the planet's center, while its magnetotail stretches hundreds of Saturn radii behind it.

<span class="mw-page-title-main">PAMELA detector</span>

PAMELA was a cosmic ray research module attached to an Earth orbiting satellite. PAMELA was launched on 15 June 2006 and was the first satellite-based experiment dedicated to the detection of cosmic rays, with a particular focus on their antimatter component, in the form of positrons and antiprotons. Other objectives included long-term monitoring of the solar modulation of cosmic rays, measurements of energetic particles from the Sun, high-energy particles in Earth's magnetosphere and Jovian electrons. It was also hoped that it may detect evidence of dark matter annihilation. PAMELA operations were terminated in 2016, as were the operations of the host-satellite Resurs-DK1. The experiment was a recognized CERN experiment (RE2B).

The following is a chronology of discoveries concerning the magnetosphere.

<span class="mw-page-title-main">Plasmasphere</span> Region of Earths magnetosphere consisting of cool plasma

The plasmasphere, or inner magnetosphere, is a region of the Earth's magnetosphere consisting of low-energy (cool) plasma. It is located above the ionosphere. The outer boundary of the plasmasphere is known as the plasmapause, which is defined by an order of magnitude drop in plasma density. In 1963 American scientist Don Carpenter and Soviet astronomer Konstantin Gringauz proved the plasmasphere and plasmapause's existence from the analysis of very low frequency (VLF) whistler wave data. Traditionally, the plasmasphere has been regarded as a well behaved cold plasma with particle motion dominated entirely by the geomagnetic field and, hence, co-rotating with the Earth.

Space physics, also known as space plasma physics, is the study of naturally occurring plasmas within Earth's upper atmosphere and the rest of the Solar System. It includes the topics of aeronomy, aurorae, planetary ionospheres and magnetospheres, radiation belts, and space weather. It also encompasses the discipline of heliophysics, which studies the solar physics of the Sun, its solar wind, the coronal heating problem, solar energetic particles, and the heliosphere.

<span class="mw-page-title-main">Magnetosphere of Jupiter</span> Cavity created in the solar wind

The magnetosphere of Jupiter is the cavity created in the solar wind by Jupiter's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary magnetosphere in the Solar System, and by volume the largest known continuous structure in the Solar System after the heliosphere. Wider and flatter than the Earth's magnetosphere, Jupiter's is stronger by an order of magnitude, while its magnetic moment is roughly 18,000 times larger. The existence of Jupiter's magnetic field was first inferred from observations of radio emissions at the end of the 1950s and was directly observed by the Pioneer 10 spacecraft in 1973.

<span class="mw-page-title-main">Van Allen Probes</span> NASA Earth magnetosphere investigator satellites

The Van Allen Probes, formerly known as the Radiation Belt Storm Probes (RBSP), were two robotic spacecraft that were used to study the Van Allen radiation belts that surround Earth. NASA conducted the Van Allen Probes mission as part of the Living With a Star program. Understanding the radiation belt environment and its variability has practical applications in the areas of spacecraft operations, spacecraft system design, mission planning and astronaut safety. The probes were launched on 30 August 2012 and operated for seven years. Both spacecraft were deactivated in 2019 when they ran out of fuel. They are expected to deorbit during the 2030s.

<span class="mw-page-title-main">L-shell</span> Mathematical parameter used to describe planetary magnetic field lines

The L-shell, L-value, or McIlwain L-parameter is a parameter describing a particular set of planetary magnetic field lines. Colloquially, L-value often describes the set of magnetic field lines which cross the Earth's magnetic equator at a number of Earth-radii equal to the L-value. For example, describes the set of the Earth's magnetic field lines which cross the Earth's magnetic equator two earth radii from the center of the Earth. L-shell parameters can also describe the magnetic fields of other planets. In such cases, the parameter is renormalized for that planet's radius and magnetic field model.

Health threats from cosmic rays are the dangers posed by cosmic rays to astronauts on interplanetary missions or any missions that venture through the Van-Allen Belts or outside the Earth's magnetosphere. They are one of the greatest barriers standing in the way of plans for interplanetary travel by crewed spacecraft, but space radiation health risks also occur for missions in low Earth orbit such as the International Space Station (ISS).

<span class="mw-page-title-main">Energetic neutral atom</span> Technology to create global images of otherwise invisible phenomena

Energetic Neutral Atom (ENA) imaging is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere.

<span class="mw-page-title-main">Solar particle event</span> Solar phenomenon

In solar physics, a solar particle event (SPE), also known as a solar energetic particle event or solar radiation storm, is a solar phenomenon which occurs when particles emitted by the Sun, mostly protons, become accelerated either in the Sun's atmosphere during a solar flare or in interplanetary space by a coronal mass ejection shock. Other nuclei such as helium and HZE ions may also be accelerated during the event. These particles can penetrate the Earth's magnetic field and cause partial ionization of the ionosphere. Energetic protons are a significant radiation hazard to spacecraft and astronauts.

<span class="mw-page-title-main">Heliophysics Science Division</span>

The Heliophysics Science Division of the Goddard Space Flight Center (NASA) conducts research on the Sun, its extended Solar System environment, and interactions of Earth, other planets, small bodies, and interstellar gas with the heliosphere. Division research also encompasses geospace—Earth's uppermost atmosphere, the ionosphere, and the magnetosphere—and the changing environmental conditions throughout the coupled heliosphere.

<span class="mw-page-title-main">JEDI</span> Radiometer and particle detector on the Juno spacecraft

JEDI (Jupiter Energetic-particle Detector Instrument) is an instrument on the Juno spacecraft orbiting planet Jupiter. JEDI coordinates with the several other space physics instruments on the Juno spacecraft to characterize and understand the space environment of Jupiter's polar regions, and specifically to understand the generation of Jupiter's powerful aurora. It is part of a suite of instruments to study the magnetosphere of Jupiter. JEDI consists of three identical detectors that use microchannel plates and foil layers to detect the energy, angle, and types of ion within a certain range. It can detect electrons between 40 and 500 keV (Kilo electron-volts), and hydrogen and oxygen from a few tens of keV to less than 1000 keV (1 MeV). JEDI uses radiation-hardened Application Specific Integrated Circuits (ASIC)s. JEDI was turned on in January 2016 while still en route to Jupiter, to study interplanetary space. JEDI uses solid state detectors (SSDs) to measure the total energy (E) of both the ions and the electrons. The MCP anodes and the SSD arrays are configured to determine the directions of arrivals of the incoming charged particles. The instruments also use fast triple coincidence and optimum shielding to suppress penetrating background radiation and incoming UV foreground.

<span class="mw-page-title-main">Solar phenomena</span> Natural phenomena within the Suns atmosphere

Solar phenomena are natural phenomena which occur within the atmosphere of the Sun. They take many forms, including solar wind, radio wave flux, solar flares, coronal mass ejections, coronal heating and sunspots.

<span class="mw-page-title-main">Explorer 12</span> NASA satellite of the Explorer program

Explorer 12, also called EPE-A or Energetic Particles Explorer-A and as S3), was a NASA satellite built to measure the solar wind, cosmic rays, and the Earth's magnetic field. It was the first of the S-3 series of spacecraft, which also included Explorer 12, 14, 15, and 26. It was launched on 16 August 1961, aboard a Thor-Delta launch vehicle. It ceased transmitting on 6 December 1961 due to power failure.

<span class="mw-page-title-main">Explorer 25</span> NASA satellite of the Explorer program

Explorer 25, was a NASA magnetically aligned satellite launched simultaneously with Explorer 24 (AD-B) using a Scout X-4 launch vehicle. This was NASA's first dual-satellite launch. The satellite's primary mission was to make measurements of the influx of energetic particles into the atmosphere of Earth and to study atmospheric heating and the increase in scale height which have been correlated with geomagnetic activity. Studies of the natural and artificial trapped Van Allen radiation belts were also conducted. A biaxial fluxgate magnetometer was used to monitor the orientation of the spacecraft with respect to the local magnetic field.

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