Plasma
Matter consists of atoms held together by electromagnetic forces. How
tight
these bonds are, determines which of the four states: solid, liquid,
gas and
plasma, matter exists as. Plasma is only found naturally in the
corona and cores
of stars and in bolts of lightning. There are three classic
states of matter:
solid, liquid, and gas; however, plasma is considered by
some scientists to be
the fourth state of matter. The plasma state is not
related to blood plasma, the
most common usage of the word; rather, the term
has been used in physics since
around the 1920s to represent an ionized gas.
Space plasma physics became an
important scientific discipline in the early
1950s with the discovery of the Van
Allen radiation belts. Lightning is
commonly seen as a form of plasma. Matter
changes its state as it is exposed
to different physical conditions. Ice is a
solid with hydrogen (H2) and
oxygen (O) molecules arranged in regular patterns,
but if the ice melts, the
H2O enters a new state: liquid water. As the water
molecules are warmed, they
separate further to form steam, which is a gas. In
these classic states, the
positive charge of each atomic nucleus equals the
total charge of all the
electrons orbiting around it so that the net charge is
zero. Each entire atom
is electrically neutral. When more heat is applied, the
steam may be ionized:
an electron will gain enough energy to escape its atom.
This atom is left
one electron short and now has a net positive charge; called
an ion. In a
sufficiently heated gas, ionization happens many times, creating
clouds of
free electrons and ions; however, not all the atoms are necessarily
ionized,
and some may remain completely intact with no net charge. This ionized
gas
mixture, consisting of ions, electrons, and neutral atoms, is called
plasma.
Plasma must have sufficient numbers of charged particles so that
the gas, as a
whole, exhibits a collective response to electric and magnetic
fields. Although
plasma includes electrons and ions and conducts electricity,
it is
macroscopically neutral. In measurable quantities, the number of
electrons and
ions are equal. The charged particles are affected by electric
and magnetic
fields applied to the plasma, and the motions of the particles
in the plasma
generate fields and electric currents from within. This complex
set of
interactions makes plasma a unique, fascinating, and complex state of
matter.
Plasma is found in both ordinary and exotic places. When an
electric current is
passed through neon gas, it produces both plasma and
light. Lightning is a
massive electrical discharge in the atmosphere that
creates a jagged column of
plasma. Part of a comet's streaming tail is plasma
from gas ionized by sunlight
and other unknown processes. The Sun is a
1.5-million-kilometer ball of plasma,
heated by nuclear fusion. Scientists
study plasma for practical purposes. In an
effort to harness fusion energy on
Earth, physicists are studying devices that
create and confine very hot
plasmas in magnetic fields. In space, plasma
processes are largely
responsible for shielding Earth from cosmic radiation, and
much of the Sun's
influence on Earth occurs by energy transfer through the
ionized layers of
the upper atmosphere. Plasma and its properties will become
very important in
the energy field, in that if its energy was captured, it would
be more
powerful than current nuclear
power.