Free Astronomy Magazine September-October 2020

SEPTEMBER-OCTOBER 2020 solar panels. This way, astronomers observ- ing a distant exoplanet will know where and what to look for if they’re searching for technosignatures,” but the database that this survey promises to produce could ulti- mately be useful only to recognize the pres- ence of any technological civilizations identical to our current one. Considering that we have been polluting the atmosphere in an evident way for about two centuries, and hoping that this will end by the end of this century (a deadline by which we could also have optimized energy production), we can assume that a civilization like ours would be recognizable by Frank's team within a time span of just 3-4 centuries, after which it might become invisible to us. It is difficult to fathom that a technological civilization could theoretically evolve slowly over millen- nia or even millions of years for us to have a large window within which to identify them. The same can be said for other technosigna- tures, such as the planetary heat surplus ex- pected in the presence of a technological civilization or the artificial lighting of the nighttime hemisphere. Within certain limits, these technosignatures could be revealed by the large telescopes under construction or about to become operational. But even in these cases, it would be reasonable to expect that a mature civilization knows how not to waste heat and how not to disperse into space artificial lighting destined for the ground. A rtificial lights lit in the nighttime hemi- sphere of an imaginary alien planet. The search for tech- nosignatures in the Milky Way also contem- plates this sce- nario. [David A. Aguilar/ Harvard- Smithsonian Cen- ter for Astrophysics]