Study of naturally occurring plasma in the Earth's atmosphere and space
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
(collectively known as
solar-terrestrial physics
[1]
). 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
.
Space physics is both a
pure science
and an
applied science
, with applications in
radio transmission
,
spacecraft
operations (particularly
communications
and
weather satellites
), and in
meteorology
. Important physical processes in space physics include
magnetic reconnection
,
synchrotron radiation
,
ring currents
,
Alfven waves
and
plasma instabilities
. It is studied using direct
in situ
measurements by
sounding rockets
and spacecraft,
[2]
indirect
remote sensing
of
electromagnetic radiation
produced by the plasmas, and theoretical
magnetohydrodynamics
.
Closely related fields include
plasma physics
, which studies more fundamental physics and artificial plasmas;
atmospheric physics
, which investigates lower levels of Earth's atmosphere; and
astrophysical plasmas
, which are natural plasmas beyond the Solar System.
History
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]
Space physics can be traced to the Chinese who discovered the principle of the
compass
, but did not understand how it worked. During the 16th century, in
De Magnete
,
William Gilbert
gave the first description of the
Earth's magnetic field
, showing that the Earth itself is a great magnet, which explained why a compass needle points north. Deviations of the compass needle
magnetic declination
were recorded on navigation charts, and a detailed study of the declination near London by watchmaker
George Graham
resulted in the discovery of irregular magnetic fluctuations that we now call magnetic storms, so named by
Alexander Von Humboldt
. Gauss and
William Weber
made very careful measurements of Earth's magnetic field which showed systematic variations and random fluctuations. This suggested that the Earth was not an isolated body, but was influenced by external forces ? especially from the
Sun
and the appearance of
sunspots
. A relationship between individual aurora and accompanying geomagnetic disturbances was noticed by
Anders Celsius
and
Olof Peter Hiorter
in 1747. In 1860,
Elias Loomis
(1811?1889) showed that the highest incidence of aurora is seen inside an oval of 20 - 25 degrees around the magnetic pole. In 1881,
Hermann Fritz
published a map of the "isochasms" or lines of constant magnetic field.
In the late 1870s,
Henri Becquerel
offered the first physical explanation for the statistical correlations that had been recorded: sunspots must be a source of fast protons. They are guided to the poles by the Earth's magnetic field. In the early twentieth century, these ideas led
Kristian Birkeland
to build a
terrella
, or laboratory device which simulates the Earth's magnetic field in a vacuum chamber, and which uses a cathode ray tube to simulate the energetic particles which compose the solar wind. A theory began to be formulated about the interaction between the Earth's magnetic field and the solar wind.
Space physics did not begin in earnest, however, until the first in situ measurements in the early 1950s, when a team led by
Van Allen
launched the first rockets to a height around 110 km. Geiger counters on board the second Soviet satellite,
Sputnik 2
, and the first US satellite,
Explorer 1
, detected the Earth's radiation belts,
[3]
later named the
Van Allen belts
. The boundary between the Earth's magnetic field and
interplanetary space
was studied by
Explorer 10
. Future space craft would travel outside Earth orbit and study the composition and structure of the solar wind in much greater detail. These include
WIND (spacecraft)
, (1994),
Advanced Composition Explorer
(ACE),
Ulysses
, the
Interstellar Boundary Explorer
(IBEX) in 2008, and
Parker Solar Probe
. Other spacecraft would study the sun, such as
STEREO
and
Solar and Heliospheric Observatory
(SOHO).
See also
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References
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Further reading
[
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External links
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