A ring of satellites surrounds Earth. Maybe we could see one around an alien world European Space Agency

One civilisation’s space trash may be another’s space treasure. Technologically advanced aliens on distant worlds could be revealed by the satellites and other space junk orbiting their planets.

When we think of signs of civilisation that may be visible around other worlds, many focus on those that require extreme technological advancement, like giant lasers or Dyson spheres – huge artificial structures that harvest power from a star.

There aren’t nearly as many ways to look for civilisations that have advanced to …