It was originally thought that Gliese 581 d orbits outside the habitable zone of its star. However, in 2009 the original discovery team revised its original estimate of the planet's orbital parameters, finding that it orbits closer to its star than originally believed. They concluded that the planet is within the habitable zone where liquid water could exist. According to Stéphane Udry, "It could be covered by a 'large and deep ocean'; it is the first serious ocean planet candidate."
