Free Astronomy Magazine July-August 2021

24 JULY-AUGUST 2021 ASTRO PUBLISHING The fact that life exists on Earth has been evident, for an external ob- server, for at least half a billion years (since the Cambrian explo- sion), therefore up to distances in space that exceed the boundaries of the local supercluster of galaxies (Laniakea). That the Earth also hosts a technological civilization is instead clearly visible only within the Orion arm of the Milky Way, up to a few hundred light-years away. Because we don’t know if other technological civilizations exist, and much less do we know how their technologies can manifest them- selves, when we go in search of them we can only hope that they Ichnoscale − the parameter for technological civilizations by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador F or some years now, astrobiolo- gists engaged in the search for possible alien civilizations have been outlining more and more con- cretely the scientific programs to be undertaken to discover technosig- natures of non-terrestrial origin. Very strictly, we can define tech- nosignatures as observational evi- dence of the existence of techno- logical applications in the universe. Discovering possible biosignatures produced by the “simple” existence of life on another planet (ET) would already be a lot, but it would be quite another thing to realize that that life has developed sufficient in- telligence to create technologies (ETI).