Radiation belt

from Wikipedia, the free encyclopedia
The powerful radiation belt of Jupiter in cross section, which the space probe Juno tries to bypass

A radiation belt is a ring ( torus ) of high-energy charged particles in space that are captured by the magnetic field of an astronomical object, its magnetosphere .

The first predicted and best studied radiation belts, the Van Allen belts of Earth , named after James Van Allen , who has shown him. In principle, every celestial body that has a sufficiently strong and stable global magnetic dipole field probably has one or more radiation belts. In the solar system , the planet with the strongest radiation belt is by far the gas giant Jupiter . Jupiter's magnetic field is around 20 times stronger than Earth's magnetic field. Its radiation belt is thousands of times stronger than that of the earth and has the hardest ionizing radiation in the solar system.

Effects

The particles buzzing in radiation belts have high speeds, up to near the speed of light , and correspondingly high energy. They are able to push electrons out of atoms or molecules . Its effect is comparable to the ionizing radiation released during radioactive decay , even if it has no radioactive cause. It can damage the electronics of rockets , space probes , satellites and other objects , and it can genetically damage , make sick and kill living organisms . For this reason, radiation belts must either be flown around in space travel , the length of stay in them must be kept as short as possible in order to limit radiation exposure , or particularly strong radiation protection is necessary.

However, radiation belts also have a certain protective effect on the planet. In 2014 the results of a NASA study were published, according to which the radiation belt, together with the Earth's plasma sphere, acts like a barrier that is almost impenetrable for high-energy electrons from space.

If radiation belts are particularly pronounced, they can react with the planet's high atmosphere and generate northern lights .

Radiation belts can also emit non-ionizing and electromagnetic radiation that can still be measured at a great distance from the planet.

Variability and zones

This video shows the variability of the Van Allen belt

Radiation belts often have several separate radiation zones, partly oval in shape or concave-convex like the letter C or the jacket of a bicycle tire , each with different characteristic particles, so that one can also speak of several radiation belts.

In practice, radiation belts are by no means uniform and constant, as idealized graphics suggest. Celestial bodies are not perfect dipoles. The planet's asymmetrical and variable magnetic field affects the shape and strength of the radiation belt. On earth, for example, the magnetosphere has a dent in the area of ​​the South Atlantic off the coast of Brazil . There is the South Atlantic Anomaly , where the atmosphere has particle radiation that is several orders of magnitude higher.

In addition, radiation belts become larger and smaller, stronger and weaker during the interaction of the variable stellar wind and the likewise variable cosmic radiation with the magnetosphere, form additional radiation zones and lose them again. Magnetic storms have an especially intense effect on radiation belts. These variations in the near-earth area of ​​the magnetosphere are also called space weather .

Emergence

Until 2013, it was assumed that the high-energy particles (free protons and electrons ) in the Van Allen Belt originate mainly from the solar wind and cosmic rays and are captured by the Earth's magnetic field . In 2013, however, scientists used probes to find out that the majority of the particles in the Van Allen Belt itself are created by the atoms being torn apart by electromagnetic fields , thereby leaching electrons.

The ionized and thus charged particles are deflected in the magnetic field as a result of the Lorentz force . They follow the magnetic field lines on spiral paths. As soon as they come near the poles , where the field lines narrow, they are deflected in the opposite direction. In this way, the particles are enclosed in a magnetic bottle and oscillate back and forth between the poles of the planet at high speed. In the Earth's Van Allen radiation belt, the period of oscillation of the particles is about one second. Seen globally, the movement of the particles is chaotic.

Known radiation belts

Earth's radiation belt

Particle density in the Van Allen belts (above: protons, below: electrons)

The Earth's radiation belt was detected in 1958 with the Explorer 1 satellite . It has an average radiation of 600  mSv / h .

To date, three radiation belts on Earth have been discovered. The "inner radiation belt" dominated by protons has significantly stronger radiation than the "outer radiation belt" dominated by electrons. The third, even further out, was temporarily available in September 2012 and then dissolved again.

When determining the orbits of earth satellites and space stations, the radiation belts must be taken into account. Geostationary satellites orbit at an altitude roughly equal to the outer edge of the outer radiation belt. Depending on the variation in the radiation belt, they are therefore repeatedly exposed to significantly increased radiation. The International Space Station, on the other hand, orbits the earth at an altitude of approx. 400 km, i.e. below the inner radiation belt.

In 2011 the Pamela experiment demonstrated that there is an accumulation of antimatter in the earth's inner radiation belt .

Jupiter's radiation belt

Jupiter's northern aurorae generated by the radiation belt. You can see the main aurora oval, further polar ovals, transpolar emissions and glowing spots that originate from the interaction of the radiation belt with Jupiter's moons

Jupiter's magnetic field is the largest coherent structure in the solar system after the heliosphere . It extends around seven million kilometers in the direction of the sun and in the opposite direction in the form of a long tail about to the orbit of Saturn . Its radiation belt is correspondingly large. Overall, this is less dependent on the solar wind and is strongly influenced by Jupiter's moons and their influence on Jupiter's magnetic field, especially inside . It creates permanent, fluctuating aurora lights at both poles of the gas giant.

Jupiter's radiation belt has radiation so hard that solar cells can not be used in it. The Pioneer 10 probe measured radiations of up to 13 million high-energy electrons / cm³, up to 500 million low-energy electrons / cm³, and up to 4 million protons / cm³. That is about 5000 times harder radiation than in the Van Allen Belt. In total, the probe absorbed a radiation dose of 5000 Gray during the passage . That is about a thousand times the lethal dose for a person.

Jupiter has a surrounding ring of magnetospheric plasma that rotates with the planet. The pressure of this plasma continually tears gas from the atmospheres of the moons (especially Io ), and this gas in turn is a major source for the rotating plasma. Along the orbit of Ios there is a separate plasma torus, which fundamentally influences the magnetosphere and thus also the radiation belt of Jupiter. During volcanic eruptions on Io, there are also strong plasma waves that can be received as Jupiter bursts in the shortwave range. They sound like surf waves or the flutter of a flag in the wind.

Strong radio waves also constantly emanate from Jupiter's radiation belt, with frequencies ranging from several kilohertz to the double-digit megahertz range. Depending on the wavelength, a distinction is made between Jovian kilometric radiation (KOM) , hectometric radiation (HOM) , or decametric radiation (DAM) . Most of this radiation is generated near the auroras by a mechanism called the Cyclotron Maser Instability . The radio and particle radiation of Jupiter is strongly modulated by its rotation, which makes Jupiter resemble a very small pulsar .

In addition to the relatively long-wave radio radiation, Jupiter also emits synchrotron radiation . This is the bremsstrahlung of the electrons trapped in the inner radiation belt, which move at a relativistic speed.

More radiation belts

Saturn's radiation belt

Saturn's radiation belts are significantly weaker than Jupiter's, only about the same as those of Earth, although its magnetic field is significantly stronger than that of Earth. This is because energetic particles are absorbed by Saturn's moons and by corpuscular matter orbiting the planet.

Saturn's strongest radiation belt is located between the inner edge of the gastorus of Enceladus and the outer edge of the A-ring at 2.3 Saturn radii . It is strongly influenced by interplanetary solar wind disturbances. The second known radiation belt of Saturn, which was discovered by the Cassini probe in 2004, lies immediately outside the innermost D-ring. Unlike the radiation belts of Jupiter, Saturn's radiation belts hardly emit any microwave radiation that the earth could detect. Yet they are strong enough to weather the surface of the ice moons and to tear away matter such as water and oxygen.

Uranus and Neptune have weaker radiation belts.

Despite its strong magnetic field, Mercury does not have a radiation belt because it is too close to the sun and the solar wind directly reaches the surface. Venus , Mars and the earth's moon have no radiation belts because their magnetic field is too weak and / or undirected.

Artificial radiation belt

In 1958, with the secret Operation Argus , the US military demonstrated that it is possible to create an artificial radiation belt using atomic bombs detonated in space . They detonated three atomic bombs at heights of 200 km, 240 km and 540 km above the South Atlantic. This created artificial electron belts that lasted for a few weeks. It was assumed that such artificial radiation belts could be used for tactical purposes in the event of war.

Individual evidence

  1. ↑ Wilhelm Raith: Earth and Planets . Walter de Gruyter, 2001, ISBN 978-3-11-019802-7 , p. 573 ( books.google.de ).
  2. ^ NASA's Juno Spacecraft to Risk Jupiter's Fireworks for Science. In: nasa.gov. NASA / JPL, accessed June 29, 2016 .
  3. ↑ Holly Zell: Van Allen Probes Spot on Impenetrable Barrier in Space. In: nasa.gov. February 12, 2015, accessed June 30, 2016 .
  4. ↑ Background: Trapped particle radiation models. In: oma.be. www.spenvis.oma.be, accessed June 29, 2016 .
  5. ^ Science - Electron Acceleration in the Heart of the Van Allen Radiation Belts by GD Reeves et. all. Science, July 25, 2013, accessed July 26, 2013 .
  6. ↑ Van Allen Belt: Researchers solve the mystery of earthly radiation rings spiegel.de, accessed on July 27, 2013
  7. ↑ David P. Stern, Mauricio Peredo: The Exploration of the Earth's Magnetosphere . NASA / GSFC. Retrieved September 27, 2013.
  8. ↑ R. Dilao, R. Alves Pires: Chaos in the Stormer trouble . In: Birkhäuser Verlag Basel (Ed.): Progress In Nonlinear Differential Equations and Their Applications . 75, 2007, pp. 175-194. doi : 10.1007 / 978-3-7643-8482-1_14 .
  9. ↑ Oscar Adriani, (et al.): The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons. In: The Astrophysical Journal Letters. Volume 737, No. 2, 2011, doi: 10.1088 / 2041-8205 / 737/2 / L29 , pp. 1–5 ( preprint article at arXiv.org; 126 kB ).
  10. ↑ Bhardwaj, A .; Gladstone, GR (2000). Auroral emissions of the giant planets (PDF). Reviews of Geophysics 38 (3): 295-353. bibcode : 2000RvGeo..38..295B . doi: 10.1029 / 1998RG000046
  11. ↑ Radiation exposure from satellites and space probes. In: bernd-leitenberger.de. www.bernd-leitenberger.de, accessed on June 30, 2016 .
  12. ↑ Andre, N .; Blanc, M .; Maurice, S .; et al. (2008). Identification of Saturn's magnetospheric regions and associated plasma processes: Synopsis of Cassini observations during orbit insertion , pp. 10-11. Reviews of Geophysics 46 (4): RG4008. bibcode : 2008RvGeo..46.4008A . doi: 10.1029 / 2007RG000238
  13. ↑ Zarka, Phillipe; Lamy, Laurent; Cecconi, Baptiste; Prangé, René; Rucker, Helmut O. (2007). Modulation of Saturn's radio clock by solar wind speed , pp. 384–385. Nature 450 (7167): 265-267. bibcode : 2007Natur.450..265Z . doi: 10.1038 / nature06237 . PMID 17994092
  14. ↑ Paranicas, C .; Mitchell, DG; Krimigis, SM; et al. (2007). Sources and losses of energetic protons in Saturn's magnetosphere . Icarus 197 (2): 519-525. bibcode : 2008Icar..197..519P . doi: 10.1016 / j.icarus.2008.05.011
  15. ↑ Wilhelm Raith: Earth and Planets . Walter de Gruyter, 2001, ISBN 978-3-11-019802-7 , p. 595 ( books.google.de ).
  16. ↑ Planet Mercury - A small hot and cold world. goerlitzer-sternfreunde.de, archived from the original on June 16, 2009 ; Retrieved October 6, 2009 .
  17. ↑ Report DNA 6039F: Operation Argus 1958 . In: Nuclear Test Personnel Review . Defense Nuclear Agency . 1982. Retrieved June 8, 2016.