Alien civilizations may be trapped on their own home worlds physical limitations may stop them from leaving their planets. Hear about it at urban legends and stranger truths the Drake equation, formulated by astrophysicist Frank Drake back in 1961, explores the question of why we still have yet to encounter an extraterrestrial civilization. The equation takes number of different factors into consideration, including the number of stars that have planets orbiting them, the rate of star formation, and the fraction of planets that could actually develop and sustain life