The first exoplanet was discovered in 1992, and currently more than 4000 exoplanets have been confirmed so far. The nearest know exoplanet is Proxima Centauri b, which is 4.25 light years away. Currently much of the search for life on exoplanets focuses on those in the habitable zone, which is the range of distances from a star where a planet's temperature allows liquid water oceans, critical for life on Earth.
