If scientists are to fully understand astrophysical and geophysical phenomena, they first must have a clear understanding of how matter behaves in the plasma state. Years before the space era, ground-based radio wave observations revealed that a region of plasma exists above Earth's electrically neutral atmosphere. The ionosphere effectively reflects most radio waves back to Earth, and it is this process that led to the region's discovery. Plasma begins to dominate Earth's environment in the ionosphere . The plasma in these layers, consisting mainly of electrons and atomic oxygen ions, is sustained by the ionizing action of solar ultraviolet radiation on the neutral atmospheric gas.
All ionospheric layers tend to merge at night.
With the advent of artificial scientific satellites, researchers measuring the characteristics of the space environment near Earth discovered that Earth's ionized atmosphere extends much higher than was originally thought. On the side of Earth facing the Sun, the magnetopause extends upward from 140 to 64,000 kilometers. The behavior of the gas in this region is controlled by Earth's geomagnetic field, and the region is, therefore, referred to as the magnetosphere . Plasma is strongly influenced by both magnetic and electric forces, and in turn, plasma particles affect the distribution of magnetic and electric fields. While most of this solar wind is deflected around Earth, some of it penetrates the magnetosphere.