Earthlike planet Gliese 581 c. Computer artwork of a hypothetical group of flying alien creatures over 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. This 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 on the horizon, eclipsed by Gliese 581 b, a sister planet in the same system.