Space junk refers to any inoperable material orbiting our planet, from spent rocket stages to defunct and damaged satellites, as illustrated here. Some debris stays in orbit, creating the potential for more debris through collisions, while other pieces eventually fall back to Earth, completely or partially burning up in our atmosphere. Credit: Astronomy: Roen Kelly; Earth image: NASA Johnson

In the 2013 movie Gravity , Russia destroys its own spy satellite with a missile, creating a cloud of shrapnel and subsequent orbital collisions that rip apart spaceships and astronauts alike. Earth orbit is a place where life imitates art: Eight years later, Moscow launched an actual missile strike on a defunct Soviet satellite, blasting thousands of pieces of metal through space and threatening the International Space Station (ISS) at the nearby altitude of 250 miles (400 kilometers). As the lethal grapeshot sped through space 10 times faster than a rifle bullet, astronauts and cosmonauts huddled in escape pods.…