August 8, 2011
PAMELA Satellite Detects Antimatter Surrounding Earth
For the first time, researchers have confirmed the existence of antimatter in the Earth's magnetosphere, BBC News reported on Sunday.
Writing in Astrophysical Journal Letters, the researchers report that they discovered a thin band of antiprotons lying in between the inner and outer Van Allen radiation belts using the PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) satellite.
Though the British news organization claims that only a small number of antiprotons were discovered, they say that the discovery "confirms theoretical work that predicted the Earth's magnetic field could trap antimatter" and that the researchers claim that "there may be enough to implement a scheme using antimatter to fuel future spacecraft."
The paper, entitled "The Discovery of Geomagnetically Trapped Cosmic-Ray Antiprotons," is set for publication in the August 20, 2011 edition of the journal. An international team of authors, including scientists from Italy, Russia, Germany, and Sweden, worked on the research.
"The existence of a significant flux of antiprotons confined to Earth's magnetosphere has been considered in several theoretical works," they wrote in the paper. "These antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers."
"A contribution from the decay of albedo antineutrons has been hypothesized in analogy to proton production by neutron decay, which constitutes the main source of trapped protons at energies above some tens of MeV," they added. "This Letter reports the discovery of an antiproton radiation belt around the Earth. The trapped antiproton energy spectrum in the South Atlantic Anomaly (SAA) region has been measured by the PAMELA experiment for the kinetic energy range 60-750 MeV."
"A measurement of the atmospheric sub-cutoff antiproton spectrum outside the radiation belts is also reported. PAMELA data show that the magnetospheric antiproton flux in the SAA exceeds the cosmic-ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton flux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth," the researchers concluded.
PAMELA, which cost more than $30 million to build and was launched on June 15, 2006, is the first satellite-based experiment dedicated to detecting cosmic radiation--specifically, antimatter components such as positrons and antiprotons.
According to the project's official website, PAMELA is "a powerful particle identifier using a permanent magnet spectrometer with a variety of specialized detectors" as well as "an instrument of extraordinary scientific potential that is measuring with unprecedented precision and sensitivity the abundance and energy spectra of cosmic rays electrons, positrons, antiprotons and light nuclei over a very large range of energy from 50 MeV to hundreds GeV, depending on the species."
"These measurements, together with the complementary electromagnetic radiation observation that will be carried out by AGILE and GLAST space missions, will help to unravel the mysteries of the most energetic processes known in the Universe," that website also said.
Image Caption: Simulated Van Allen Belts generated by a plasma thruster in tank #5 Electric Propulsion Laboratory at the then-called Lewis Research Center, Cleveland, Ohio. Credit: NASA
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