Where does outer space begin?

Outer space begins at the top of the atmosphere, which is about 1 000 miles above our heads. The Solar System is somewhat like a small sea In the vast ocean of outer space. We call the distances between the planets interplanetary space   but beyond the planet Pluto, this interplanetary space merges with outer space, just as the spa ll seas on the earth merge with the world ocean.

The space between the planets merges with the space between the stars which form the great Milky Way. The space beyond the Milky Way merges with the space between countless other Milky Way star systems. And this vast ocean of space begins about 1,000 miles above our heads.