NASA telescopes have discovered that, so far, is the smallest planet discovered outside our solar system, being part of something like a miniature planetary system. The planet is located in a system 210 light years from Earth and has been named Kepler-37b. As you can see in the image below comparative, the little planet is approximately equal to the size of the Moon, which indicates to what extent they are able to refine the systems current planet detection.
The project of the NASA Kepler is designed to find extrasolar planets located in the habitable orbit of a star, ie, in an area not too close or too far away to be found that life as we know it and liquid water. As technology advances can discover even more distant planets and smaller as the Kepler-37b, although in this case it appears that the surface temperature of the planet is not very conducive for life to exist: more than 400 degrees Celsius because it is closer to its star than Mercury is to our Sun
