宇宙空間
Outer space, also simply called "space", refers to the relatively empty regions of the Universe outside the atmospheres of celestial bodies. "Outer" space is used to distinguish it from airspace (and terrestrial locations). There is no discrete boundary between Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the Solar System is called interplanetary space, which passes over into interstellar space at what is known as the heliopause.