Earthlike planet Gliese 581 c. Computer artwork of a hypothetical view across a body of water on the extrasolar planet Gliese 581 c. Gliese 581 c is the most Earth-like alien planet yet discovered, lying about 20.3 light years away, in the constellation Libra. There is special interest in this planet as it is the only known extrasolar planet where liquid water, a necessary ingredient for life as we know it, could exist. Here, the planet's red dwarf host star (Gliese 581) can be seen low in the sky.