Physics of solar system plasmas

Описание

Space physics
Most of the visible matter in the universe exists as a fluid composed of electrically
charged particles rather than as a gas made of neutral atoms or molecules. Gas
mixtures of electrically charged particles, such as electrons and ions, are called
plasmas. Plasmas are found in the following solar system environments; the solar
atmosphere, the interplanetary medium, planetary magnetospheres, and planetary
ionospheres. Most of the interstellar medium is also plasma, as are most other
regions of our galaxy.
Most of the plasma found in our own solar system is accessible to in situ mea-
measurements made by instruments onboard spacecraft. Since the advent of the space
age in the late 1950s, space probes have visited Mercury, Venus, Mars, Jupiter, Sat-
Saturn, Uranus, Neptune, and comets Giacobini-Zinner, Halley, andGrigg-Skjellerup,
The space environment surrounding the Earth has also been extensively studied by
experiments onboard rockets and satellites. The Sun and astrophysical plasma en-
environments outside our own solar system are not subject to direct measurements
but must be observed remotely with sophisticated instruments located either at
ground-based observatories or on orbiting observatories. An exception to this are
the very energetic particles called cosmic rays, which can be observed using Earth-
based or balloon-borne experiments. Solar cosmic rays have energies up to about
100 million electron volts A00 MeV) and originate in the solar corona. (Note that
1 MeV = 106 eV and 1 eV — 1,602 x 10~19 J,) Galactic cosmic rays permeate our
galaxy and have energies that can greatly exceed 1 GeV A GeV = 109 eV). The
plasma in the terrestrial ionosphere can also be studied remotely using either radio
wave reflection or radar backscatter techniques. In fact, the ionosphere was first dis-
discovered by means of radio reflection early in this century. The study of solar system
plasmas is commonly given the name space physics or space plasma physics^ and
this is the subject matter of this textbook.
1.1 Plasmas
Plasmas behave differently than neutral gases mainly as a consequence of the
Lorentz force. You will recall from your basic physics education that in the presence

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