planets, but have set upper limits on the masses of the outer three planets: planet b is , planet d is , and planet e is . Searches for circumstellar discs show no evidence for a debris disc similar to the Kuiper belt around Mu Arae. If Mu Arae does have a Kuiper belt, it is too faint to be detected with current instruments. The gas giant planet "b" is located in the liquid water habitable zone of Mu Arae. This would prevent an Earth-like planet from forming in the habitable zone, however large moons of the gas giant could potentially support liquid water. On the other hand, it is unclear whether moons sufficiently massive to retain an atmosphere and liquid water could actually form around a gas giant planet, due to a theorized scaling law between the mass of a planet and its satellite system. In addition, measurements of the star's ultraviolet flux suggest that any potentially habitable planets or moons may not receive enough ultraviolet to trigger the formation of biomolecules. Planet "d" would receive a similar amount of ultraviolet to the Earth and thus lies in the ultraviolet habitable zone. However, it would be too hot for any moons to support surface liquid water. See also 55 Cancri Exoplanet Lists of exoplanets PSR B1257+12 Notes References External links GJ 691 HR 6585 Image Mu Arae Extrasolar Planet Interactions by Rory Barnes & Richard Greenberg, Lunar and Planetary Lab, University of Arizona Ara (constellation) Arae, Mu CD-51 11094 G-type main-sequence stars G-type subgiants 0691 160691 086796 6585 Planetary systems with four confirmed planets