Clarke Belt

A Clarke Belt or Clarke Orbit is the stationary orbit for a particular planet, and for ours about 36,000 km above the Earth. This band can become quite extensive, forming a physically connected ring around the planet. It may need to be stabilized from drifting by tethering the structure to the planet below with multiple beanstalks. A Clarke ring can be a quite sizable megastructure and is often able to house as many citizens as its planet. This, and the constant transport of beings between the two, necessitates that the space elevators be very robust and on some worlds the beanstalks themselves can house millions.

With SETI, Arthur C. Clarke proposed looking for large bands of satellites in distant star systems, and this first came to be known as a Clarke Belt. This network forms the backbone of telecommunications and a global internet. Such a belt of artificial satellites could be considered technosignatures or technomarkers (the analogues of biomarkers, which indicate the presence of life). This is similar to a Dyson Sphere or other forms of megastructures.

Humanity currently has about 500 operational satellites occupying Earth’s “Clarke Belt”. This is about one-third of the Earth’s existing satellites, whereas the rest are at an altitude of 2000 km (1200 mi) or less from the surface – the region known as Low Earth Orbit (LEO). Billions more satellites would be needed in order for it to be detectable. Given the rate of exponential growth, humanity will reach the threshold where its satellite band will be detectable by ETIs by 2200 and therefore a viable option for SETI.