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Throughout the universe more than 99 percent of matter looks nothing like what's on Earth.

This material that pervades the universe, making up the stars and our sun, and also – far less densely, of course – the vast interstellar spaces in between, is called plasma. Plasmas are similar to gases, and indeed are made of familiar stuff such as hydrogen, helium, and even heavier elements like iron, but each particle carries electrical charge and the particles tend to move together as they do in a fluid.

"Which particles are moving, what is the source of energy for the motion, how does a moving wave interact with the particles themselves, do the wave fields rotate to the right or to the left – all of these get classified," says Lynn Wilson who is a space plasma physicist at NASA's Goddard Space Flight Center in Greenbelt, Md.

Magnetic pressure

Magnetic pressure is an energy density associated with the magnetic field.

Interplay between magnetic pressure and ordinary gas pressure is important to both the fields of magnetohydrodynamics and plasma physics. Any magnetic field has an associated pressure that is contained by the boundary conditions on the field, and a gradient in field strength causes a force due to the magnetic pressure gradient; this force is called the magnetic pressure force.