As we explore outer space, we are also been creating a bit of a mess. Orbiting our planet are thousands of dead satellites, along with bits of machinery from all the rockets we’ve launched over the years. And one day, these objects that we leave in space – which are called space debris or space junk – could pose serious issues.

All space junk are man-made objects launched from Earth, which remain in orbit until they re-enter the atmosphere. Some objects in lower orbits of a few hundred kilometres often re-enter the atmosphere quite fast and then burn up before reaching the ground. But junk and dead satellites that are left at higher altitudes of 36,000 kilometres, can continue to circle Earth for hundreds or even thousands of years.

Even the smallest pieces of space junk can travel at speeds up to 28,000 kilometres per hour, presenting great risks to satellites functioning around the Earth. As a result of this, they have to actively move out of the way to avoid getting hit. In total, across all satellites, hundreds of collision avoidance manoeuvres are performed every year, including by the International Space Station (ISS), where astronauts live. Fortunately, collisions scarcely happen and when they do, there has been no serious loss.

The United Nations have called for the removal of satellites from orbit, and several companies around the world have come up with creative solutions, including removing dead satellites from orbit and dragging them back into the atmosphere, where they will burn up. However, these methods are only useful for large satellites orbiting Earth. For now, we can only wait for smaller pieces of debris to naturally re-enter Earth's atmosphere.

(Adapted from nhm.ac.uk/discover)