 Two previously discovered planets in the same system, Gliese 581 c and d (inward and outward from planet g, respectively), were also regarded as potentially habitable following their discovery. Both were later evaluated as being outside the conservatively defined habitable zone, leading Vogt et al. to remark that "The GJ 581 system has a somewhat checkered history of habitable planet claims". However, a subsequent downward revision of the period of planet d from 83 to 67 days has bolstered its habitability prospects, although a large greenhouse effect would be needed.
