As of July 2014, astronomers have discovered 1,739 confirmed exoplanets and 452 multiplanet solar systems. There are also an additional 4,234 unconfirmed planets detected by the NASA Kepler observatory. According to their sizes, the confirmed planets include 107 that are Earth-sized. About 47 of all confirmed planets are located in the habitable zones of their stars -- the distance from a star where liquid water might pool on the surface.
Let's take a look at one of the most intriguing ones that is both Earth-sized and in the habitable zone of its star. It's called Kepler-186f, which means its the fifth planet (b, c, d, and e are the others) orbiting the star Kepler-186.