Amit Oren
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A great mystery began several years ago when a spacecraft designed to measure Gamma-Ray Bursts (GRBs) - the most powerful explosions in the universe - discovered that Earth emits some of these flashes itself.
These bursts, known as Terrestrial gamma-ray flashes (TGFs), last approximately one thousandth of a second, and are emitted into space from the upper atmosphere of the Earth. Scientists believe that electrons traveling at near the speed of light hit atoms and slow down in the upper atmosphere, thus emitting the flashes.
The Burst and Transient Source Experiment (BATSE) on the Compton gamma-ray satellite discovered terrestrial flashes in 1994, but was limited in its ability to count them or measure energy peaks. New observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite raise the maximum energy of the flashes recorded by a factor of 10 and show that KDA releases about fifty flashes every day, and possibly even more.
"The energies we see are as high as the gamma rays emitted by black holes and neutron stars," said David Smith, assistant professor of physics at the University of California, Santa Cruz, and author of a scientific paper on the subject.
The specific mechanism that accelerates the electron beams to produce the flashes is not yet clear, Smith said, but it must be accompanied by the formation of an electrical charge on lightning clouds due to a lightning discharge. The process ends with the formation of a strong magnetic field between the tops of the clouds and the ionosphere - the outer layer of the Earth's atmosphere.
Terrestrial gamma-ray flashes have been associated with lightning strikes and may be associated with "red sprites" and "blue jets," side effects of lightning storms in the upper atmosphere typically seen only with high-altitude aircraft and satellites. Despite this, the direct relationship between all the events is still unclear.
RHESSI was launched in 2002 to examine X-rays and gamma rays from solar flares, but its detectors pick up gamma rays from a variety of sources. While scientists estimate a global average of 50 flashes per day, the number could reach 100 times more if, as some models suggest, terrestrial gamma-ray flashes are emitted as barely focused rays that will only be detected when the satellite is precisely in their orbit.
For information on the NASA website
Yedan - Earth - Planet
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