interplanetary medium

The interplanetary medium (IPM) is matter such as dust, gas, and plasma within the solar system between planets. The plasma is solar wind, a substantial part of the IPM. IPM density varies, generally thinner away from the Sun (a steady solar wind would decrease in density according to an inverse square law). The density at 1 AU (i.e., the vicinity of Earth) is on the order of 5 particles per cubic centimeter. Given the electrically-conducting plasma, a magnetic field is maintained, forming a dynamo. The dust, known as interplanetary dust particles (IDP), is generally dust fragments of asteroids, etc.

Analogous matter between stars is called the interstellar medium and between galaxies, the intergalactic medium.