The generally accepted border between Earth's atmosphere and outer space is the Kármán line, located approximately 100 kilometers (62 miles) above mean sea level.
Understanding the Kármán Line
The Kármán line is not a sharply defined physical boundary, but rather a conventional definition. It's the altitude where the atmosphere becomes too thin for aerodynamic flight. At this height, a vehicle would need to travel at orbital velocity (approximately 28,000 km/h or 17,500 mph) to generate enough lift to support itself. Below this line, airplanes can fly. Above it, spacecraft can orbit.
Several sources confirm this:
- Wikipedia: The Kármán line is a conventional definition of the edge of space, not universally accepted. https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line
- Britannica: The Kármán line is a boundary separating Earth's atmosphere and outer space, but it's neither sharp nor well defined. https://www.britannica.com/science/Karman-line
- NASA: NASA's ICON satellite studies the ionosphere, a region within the upper atmosphere that helps form the boundary between Earth's atmosphere and space. https://www.nasa.gov/missions/icon/nasas-icon-explores-the-boundary-between-earth-and-space/
- Space.com: The Kármán line is a boundary 62 miles (100 kilometers) above mean sea level that borders Earth's atmosphere and the beginning of space. https://www.space.com/karman-line-where-does-space-begin
While the Kármán line is widely used, it's important to remember that the Earth's atmosphere gradually thins with altitude; it doesn't end abruptly.
Practical Implications
- Spaceflight: The Kármán line serves as a practical guideline for defining the boundary between aeronautics and astronautics.
- International Recognition: The Fédération Aéronautique Internationale (FAI) uses the Kármán line to define the beginning of space for record-keeping purposes.
- Legal and Regulatory Purposes: While not universally legally binding, it informs many legal and regulatory frameworks concerning space activities.
