Gliese 581 d

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Gliese 581 d (Template:PronEng), also cataloged as HO Librae d, is a plausible extrasolar planet approximately 20 light-years away in the constellation of Libra. Because of its mass, the planet is classified as a super-Earth planet. Because the planet orbits in the outer edge of its parent star's habitable zone, it is thought that the planet may be similar to Earth.

Discovery

The planet was discovered by the team of Stéphane Udry of the Geneva Observatory in Switzerland using the HARPS instrument on the European Southern Observatory 3.6 meter telescope in La Silla, Chile on 24 April 2007. Udry's team employed the radial velocity technique, in which the size and mass of a planet are determined based on the small perturbations it induces in its parent star’s orbit via gravity.

The team is confident that the planet exists but recognizes that unlikely events could mimic its existence. They believe the issue will be settled by upcoming studies.

Climate and habitability

Although Gliese 581 d orbits outside the theoretical habitable zone of its star, scientists surmise that conditions on the planet may be conducive to supporting life.^[1]^[2] Scientists originally believed that Gliese 581 d would in fact be too cold for liquid water to exist, and therefore could not support life as we understand it. However, since it is calculated that the Earth's temperature would be about minus nineteen degrees celsius without any greenhouse gases, and due to a theorized greenhouse effect of Gliese 581 d, research now suggests that atmospheric conditions on the planet could create temperatures at which liquid water can exist, and therefore the planet may be capable of supporting life.