- Plasma - The Other 99.9%
- By Ian Tresman
- How do you see the Solar System? The simple view is gas
giants and rocky asteroids and planets moving through nearly empty space.
The sophisticated view shows the heliospheric current sheet, a component
of the interplanetary plasma we call the Solar Wind, awash throughout the
- Over 99.9% of the universe is made of plasma, including
the Sun and all stars, and most of the space in between. So if you don't
know the basic properties of plasmas, then you might not understand the
properties of most of the universe.
- Did you know...
- 1. Plasmas are formed by adding energy to gas, causing
it to ionize (an atom looses one or more electrons). For example, if hydrogen
ionizes, it produces equal numbers of negatively charged electrons and
positive ions (in this case, protons). Even a one percent ionized gas may
be considered to be a plasma, and have the properties of a fully ionized
- 2. Plasmas are affected by electromagnetic forces a
thousand billion billion billion billion times greater than the force of
gravity. So strong is its influence that it creates the ballerina's skirt
shaped heliospheric current sheet, the largest structure in the Solar System,
extending out beyond the orbit of Pluto.
- 3. Plasma is not always electrically neutral. In general
it is quasi-neutral, meaning that localized regions of charge separation
may occur. And objects that comes into contact with a plasma will charge
negatively, such as dust, spacecraft and the surface of the Moon.
- 4. Plasma is a better conductor of electricity than
copper. Its conductivity and response to electromagnetic influences distinguishes
it from a gas. Indeed, metals can be classified as plasma, too, because
they contain free electrons.
- 5. Moving plasma can self-generate electromagnetic fields.
- 6. Plasma can store energy in magnetic fields.
- 7. Plasmas form double layers between regions of different
densities, temperatures or magnetic field strengths. A double layer:
- (a) consists of two layers of opposite charge
- (b) tends to form cellular structures with the double
layer as the "cell wall." (eg. magnetosphere, photosphere, heliosphere)
- (c) can form in filamentary current channels known as
"Birkeland currents" (see below);
- (d) can explode, as discovered in mercury rectifiers
used in high-power direct-current transmission lines;
- (e) can accelerate charged particles, in opposite directions
up to velocities approaching the speed of light.
- 8. Relative movement of different plasma regions produces
electric currents within them.
- 9. Electric current in plasma produces "pinched"
filaments known as Birkeland currents. Birkeland currents form the cosmic
power lines and the "wires" of cosmic circuits. An example is
found in the ionosphere where these filaments carry up to a million amps,
and power the aurora. Those in the Sun's prominences have been estimated
to carry up to 100 billion amps (1011 A).
- 10. Birkeland currents collimate "jets" of
matter and charged particles. Astronomical "jets" were so named
by astrophysicists because they look somewhat like fluid jets produced
in the laboratory. Yet astronomical jets look nothing like a supersonic
jet coming out of a nozzle, with all the attendant fluid instabilities.
Heated gas should quickly disperse in space but the magnetic pinch of a
Birkeland current can maintain filaments of glowing matter over thousands
of light years.
- 11. Synchrotron radiation from pinched current filaments
can be in the form of x-rays and gamma rays.
- 12. T he pinch effect can be used in nuclear fusion reactors.
- 13. Plasma phenomena scale in size over at least 14
orders of magnitude. So the same phenomena may be seen in a dense laboratory
plasma and a tenuous space plasma.
- 14. Parallel plasma filaments attract one another with
a force inversely proportional to their distance apart. Compare this with
gravity, which attracts matter with a force inversely proportional to the
SQUARE of the distance. That makes pinched Birkeland currents by far the
most effective way of condensing rarefied dust and gas to form molecular
clouds and stars.
- So, since the Universe is 99.9% plasma, the important
question is not IF the properties of plasma are important in cosmology,
but HOW come we focus on the puny force of gravity?
- "The space data from astronomical telescopes should
be treated by scientists who are familiar with laboratory and magnetospheric
physics, circuit theory, and of course modern plasma physics." Hannes
Alfvén, Double Layers and Circuits in Astrophysics, IEEE Transactions
on Plasma Science, Vol. PS-14, No. 6, December 1986.
- Archived TPODS related to "Plasma" may be read