Mu Arae
Mu Arae is a 5th magnitude yellow-orange G-type star similar to our Sun. It lies about 49.8 light years away and is found in the constellation Ara (the Altar), where it is visible with the naked eye. It is estimated to have about 108% of the Sun's mass and may be about 32% larger. It has about 1.7 times the luminosity of the Sun and is suspected to be older, moving into the subgiant phase of its stellar evolution. Mu Arae is metal-rich, even more so than our Sun.
At least three extrasolar planets have been discovered orbiting Mu Arae, including one which scientists believe to be the first rocky extrasolar planet discovered around a main sequence star.
Planetary system
As of August 25, 2004, there were three planets believed to be orbiting Mu Arae. Two are suspected to be gas giants, one of which is the size of Jupiter and orbits with a period of 650 days. This planet's discovery was announced December 11, 2000. By June 2002 astronomers suspected the existence of another planet, believed to lie further out from the star. Observations made at La Silla to gather data regarding this object confirmed its existence and revealed the existence of a third planet.
The third planet discovered is the least massive extrasolar planet found around a main sequence star, by its discovery date of August 25, 2004, with a mass just 14 times that of Earth. It orbits very close to Mu Arae, completing one revolution every 9.5 days. The discovery was made with the aid of the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, at the European Southern Observatory's La Silla Observatory in Chile. The data that revealed the presence of this planet was gathered on 8 nights of observations in June 2004.
According to current models of planet formation, ESO scientists believe that the planet is likely to be a rocky planet, not a gas giant. At 14 Earth masses, this would theoretically be at the limit of a terrestrial planet. If true, this would likely be the first rocky planet discovered outside our Solar System orbiting a main sequence star. The surface of the planet is very hot because of its closeness to Mu Arae. It is estimated that the surface temperature would be about 900K. A rocky planet this size could possibly have formed, since Mu Arae has a higher metallicity than Sol. The probability of life as we know it existing on this planet is extremely small.
None of the three planets orbiting Mu Arae are directly visible from Earth using currently available tools. All three were found using the radial velocity method of extrasolar planet detection.
Other resources
See also
