EARTH X SPACE

There is general agreement that ‘space’ starts where the Earth’s physical influence ends or is significantly displaced, but no consensus as to where that line actually lies. Does space begin where the Earth’s atmosphere ends? That would seem sensible, except the atmosphere extends some 800 kilometres above the planet. That would exclude Gagarin’s flight, and the International Space Station (ISS) whose orbit around the Earth is only 400 kilometres high. Earth’s gravity might well seem like another natural candidate for ‘edge of space’ status, but you have to travel 21 million kilometres before our planet’s gravity loses out to other forces, and that’s roughly halfway to Venus.