Where does the atmosphere end and space begin?
FÃ©dÃ©ration AÃ©ronautique Internationale has theoretically demarcated the beginning of space by the KaÌrmaÌn Line, 100 km above mean sea level. At this altitude, a conventional aircraft would need to attain orbital velocity or risk falling back to Earth. However, according to NASA, "There is no hard-definable point where space begins... the atmosphere just gradually decreases the higher you get."