In 1961 astronomers had not yet discovered a single planet orbiting a star other than the sun. (discovermagazine.com)
Such worlds orbit stars in so - called «habitable zones,» regions where planets could hold liquid water that is necessary for life as we know it. (sciencedaily.com)
During the past 5 years, scientists have discovered more than 50 planets orbiting stars other than our sun — or so they think. (sciencemag.org)