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34 JULY-AUGUST 2022 ASTRO PUBLISHING by Michele Ferrara revised by Damian G. Allis NASA Solar System Ambassador The Drake equation doubles I n the early 1960s, astronomer Frank Drake proposed an equation de- signed to provide an estimate of the number of planets inhabited by intelligent species capable of com- municating with the homologous species of other planets. That equa- tion, still discussed today, is ex- pressed in the following form: N = R * f p n p f l f i f c L where N is the value searched, R * the star formation rate of our galaxy, f p the fraction of stars with planets, n p the number of habitable planets per star, f l the fraction of those planets that developed life, f i the fraction of the latter on which there is intelligent life, and f c the fraction of planets where intelli- gent life is able to communicate through technology. Finally, we have L , a most controversial term, which accounts for the average time during which a technological civilization sends detectable signals, consequently providing an estimate of the number of communicative species at any given time. Beyond some questionable aspects, the Drake equation has a remark- ably visionary quality. Consider that, when it was formulated, only R * was barely known, while all the other terms had to assume the exis- tence of exoplanets, the first of which was only discovered thirty years after the drawing up of the equation. It was probably that pre- dictive ability that kept it in vogue until today, despite the many radi- cal transformations that astronom- ical research has brought to our un- derstanding of the cosmos.