There's no single, universally agreed-upon answer to where space begins. However, the most widely accepted definition uses the Kármán line, situated at an altitude of 100 kilometers (62 miles) above sea level.
The Kármán Line: A Practical Demarcation
The Kármán line serves as a practical boundary for space treaties and aerospace record-keeping. While the atmosphere gradually thins with altitude, the Kármán line represents the point where an aircraft would need to travel faster than orbital velocity to generate sufficient lift to stay aloft. Below this line, aerodynamic flight is feasible; above it, orbital mechanics dominate.
Several sources confirm this:
- Wikipedia: "[The Kármán line], an altitude of 100 km (62 mi) above sea level, is conventionally used as the start of outer space in space treaties and for aerospace records keeping." (https://en.wikipedia.org/wiki/Outer_space)
- Space.com: "Earth ends and outer space starts at the Kármán line, some 62 miles (100 kilometers) above the planet's surface." (https://www.space.com/karman-line-where-does-space-begin)
- Astronomy.com: "Earth ends and outer space starts at the Kármán line, some 62 miles (100 kilometers) above the planet's surface." (https://www.astronomy.com/space-exploration/the-karman-line-where-does-space-begin/)
- Scientific American: "Currently, the generally accepted demarcation line is 100 kilometers above Earth's surface, but that value hasn't been rigorously defined..." (https://www.scientificamerican.com/article/where-does-outer-space-begin/)
Alternative Perspectives
It's important to note that different organizations may use slightly different altitudes. For instance, NASA and the U.S. military sometimes use 50 miles (80 kilometers) as a reference point. The precise demarcation remains a matter of convention rather than a strictly scientific definition. The atmosphere's gradual thinning makes a precise boundary difficult to define.
