Väliskiht

Väliskiht is an Estonian term that translates to "outer layer" or "exosphere" in English. It is most commonly used in scientific contexts, particularly in astronomy and atmospheric science. In astronomy, it refers to the outermost region of a celestial body's atmosphere. For instance, the exosphere of the Sun is its outermost layer, where the Sun's atmosphere gradually fades into outer space. This region is characterized by very low density, with particles moving freely and infrequently colliding with each other.

In the context of Earth's atmosphere, väliskiht specifically denotes the exosphere, the uppermost layer. This layer begins at an altitude of about 500-1,000 kilometers above the Earth's surface and extends outwards to about 10,000 kilometers. Particles in the exosphere are so sparse that they rarely collide and can escape Earth's gravitational pull. This is also where phenomena like the Van Allen radiation belts are located. The concept of väliskiht is crucial for understanding the interaction between a planet and its space environment, including phenomena like space weather and atmospheric escape.