are we alone?

This question is as old as humankind itself. For millennia, people have turned their eyes to the stars and wondered if there are others like themselves out there.  

Does life, be it similar to our own or not, exist elsewhere in our Solar System? Our Galaxy? Until 1992, when the first exoplanet was confirmed, it was uncertain whether there were even any planets outside those in our own Solar System. Today we know of over 900 planets around other stars and thousands of planet candidates. Do any of these planets have conditions that would support life? What conditions favor the formation of terrestrial-class planets in developing planetary systems? NASA can help address these questions by developing missions designed to find and characterize extrasolar planetary systems.

Before we can determine if there are other planetary systems capable of supporting life, we must first find them. NASA Science pursues this goal by supporting a focused suite of ground-based observations through the Kepler mission, a space-based observatory which studied the prevalence (how many there are per star) of extrasolar planets, and through the development of the TESS mission which will use an array of telescopes to perform an all-sky survey to discover transiting exoplanets ranging from Earth-sized to gas giants.

-- NASA Science [Astrophysics]