Expert: Philip A. Stahl - 9/6/2008

Question
Philip,
In the dicta of an article I read recently it listed the various baryonic matter we know of (it was about dark matter). I was suprised to find that a great deal of plasma exists in space. I thought that plasma required huge energy to create and keep the particles seperate. How can plasma exist in the cold of space? If there is no short answer, can you recommend a book or two? (something a lawyer with a science undergrad could understand)

Answer
Hello,

I think you are confusing two different domains of plasma. You are thinking of "hot plasma" such as in the Sun's core, wherein the temperatures can reach 10^7 K and protons, electrons are essentially all stripped from their base atoms (fully ionized) paving the way for nuclear fusion at high density.

However, "cold plasma" can also exist, such as for the aurora - at temperatures around 10^2 K. In this case, the plasma is more partially ionized, rather than fully ionized. This fraction of ionization can be as low as ~ 1%.

Even so, the kinetic temperatures can be quite high - but bear in mind "kinetic temperature" is a measure of the kinetic energy of the particles. IF one has a very sparsely dense gas (e.g. in the outer regions of an emission nebula), even at a very high kinetic temperature, one would not feel a thing on inserting a finger into it, if one could. (Since a "burn" is registered only if the mass of the medium is sufficient to magnify the kinetic energy to cause it - with high density of the hot gas)

The Sun's corona is a plasma at a temperature (kinetic) of 2 million K, yet if I were to thrust a finger into it, nothing would happen. No burn. The reason is because it's a near vacuum and not dense enough to impart tissue damage.

There are in addition, "thermal" and "non-thermal" plasmas in space, with the former defined by a thermal equilibrium existing between electrons and (heavy) ions at the same (relatively high) temperature. Meanwhile, non-thermal plasma exhibits electrons at much higher temperature with heavy ions at much lower temperature (usually room temp.)

I know this must all seem confusing, but fortunately there is an excellent basic book on plasmas which may still be available. No arcane equations (such as you may find in some of the previous answers) - but lots of useful diagrams.

It is: 'The Fourth State of Matter' by Yaffa and Shalom Eliezer (1989) Adam Hilger Publishers.

Hopefully, it is still available!