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Gliese 581g, unofficially known as Zarmina's World, is an unconfirmed (and disputed) exoplanet claimed to orbit within the Gliese 581 planetary system, twenty light-years from Earth. It was discovered by the Lick–Carnegie Exoplanet Survey, and is the sixth planet found orbiting the star (Gliese 581 f was found to be an artifact); however, its existence could not be confirmed by the European Southern Observatory (ESO) / High Accuracy Radial Velocity Planet Searcher (HARPS) survey team, and its existence remains controversial. It is thought to be near the middle of the habitable zone of its star. That means it could sustain liquid water—a necessity for all known life—on its surface, if there are favorable atmospheric conditions on the planet.