Kármán line is a boundary used to define where Earth’s atmosphere ends and outer space begins. It is most commonly set at an altitude of 100 kilometers (62 miles) above mean sea level. The line is named after Theodore von Kármán, an aerospace engineer and physicist who analyzed the point at which the atmosphere becomes too thin for conventional aircraft flight. His work showed that above a certain altitude, a vehicle would need to travel so fast to generate aerodynamic lift that it would effectively have to operate as an orbital spacecraft rather than as an airplane.
Aircraft remain airborne because their wings generate lift by moving through sufficiently dense air. As altitude increases, atmospheric density decreases rapidly. At extremely high altitudes, the atmosphere becomes too thin for wings to produce enough lift without the vehicle traveling at orbital velocity. Near the altitude associated with the Kármán line, the speed required for aerodynamic flight approaches the speed needed to remain in orbit around Earth. Beyond that region, orbital mechanics become more important than aerodynamics.
Although the 100-kilometer definition is widely accepted internationally, it is a convention rather than a sharp physical boundary. Earth’s atmosphere does not end abruptly at a specific height, instead, it gradually thins into space over hundreds and even thousands of kilometers. Different organizations and researchers have used slightly different altitudes for defining the edge of space. Because the atmosphere extends beyond 100 kilometers and satellites can still encounter atmospheric drag at much higher altitudes, the Kármán line should be understood as a useful operational and legal convention rather than an absolute physical border between Earth and space.
