ekzosfer

Ekzosfer, or the exosphere, is the outermost layer of Earth’s atmosphere, extending from roughly six hundred kilometers up to about ten thousand kilometers above the planet’s surface and fading into interplanetary space. There is no sharp boundary between the exosphere and space; the atmosphere becomes increasingly tenuous and particle collisions become exceedingly rare.

In the exosphere, the density of particles is extremely low and the behavior of atoms and molecules is governed by gravitational and solar-energy forces rather than frequent collisions. Particles in this region can follow ballistic trajectories back toward lower layers, remain bound in weakly curved orbits around Earth, or escape into space if their velocities exceed escape velocity.

Composition is dominated by the lightest species that remain gravitationally bound, primarily hydrogen and helium, with trace amounts of heavier species such as atomic oxygen and various ions originating from the upper atmosphere and meteoric material. The exact composition varies with solar activity and atmospheric loss processes.

Temperature in the exosphere is driven by solar radiation; the term “temperature” here reflects the average kinetic energy of particles rather than a state of thermal equilibrium, and it can be very high despite the low density. Escape processes, notably Jeans escape (thermal) and non-thermal mechanisms such as photoionization and charge exchange, contribute to the gradual loss of atmospheric material to space.

The exosphere is of interest for understanding atmospheric evolution, the boundary with space, and the environment encountered by satellites and spacecraft. It is studied using ultraviolet observations and measurements from instruments on orbiting spacecraft.