On Earth, matter mainly comes in three forms:
But in space, a fourth state prevails: the plasma state.
Electrically charged gas
Plasma is electrically charged (ionized) gas, a mixture of electrons (with negative electrical charge) and positive charged ions. Most of the visible universe (99% of it) is made of plasma. Plasma is very sensitive to electric and magnetic fields.
In order to study the solar wind, researchers investigate its:
- plasma temperature
- the kinds of particles it contains
Speed is also a key parameter. For instance, there exists a slow solar wind (400 km/sec) and a fast solar wind (800 km/sec) which originate from different regions of the Sun. In that respect, the temperature of the solar corona is an important parameter, just like gravitation and magnetic field strength is.
To conclude, researchers also investigate the energy that the solar wind carries with it.