Mu Arae
(1.90 ± 0.10 ) L ☉
My Arae ( μ Arae ) is a yellow- orange, sun -like star with an apparent magnitude of 5.1 like in the northeast corner of the constellation Altar (Ara ), where he can be seen with the naked eye under good conditions. He is in the spectral class G and in the luminosity class V - IV to classify. The star is about 50 light-years away from our sun. Its diameter is about 1.4 times its mass about 1.1 times that of the sun; equivalent to approximately 360,000 Earth masses. From the difference in brightness between μ Arae and the sun can be assumed that the star is already developed and also older than the 4.6 billion years the sun. He is also very metal- rich.
In order μ Arae four planets have so far been detected, of which the first rocky planet discovered seems to be a main sequence star.
Planetary system
In August 2006, four planets in the My Arae system were known. Three of them have a high mass and are probably so-called gas giants. The innermost planet is comparable in mass to Uranus and is either terrestrial nature or a small gas planet.
Discovery history
My Arae b - - In 2001, the discovery of the first planet was announced by a team of American and Australian researchers. The planet moves in an eccentric orbit, and orbits its star once every 743 days. It was discovered by means of a measurement of the radial velocity of My Arae (measurement of the Doppler shift of the spectral lines of the star ).
Further observations led to the discovery of a second object (My Arae c ), with which one went public in 2004. It was thought at that time that it was a planet with a highly eccentric orbit, the need for a circulation 8.2 years.
In the same year followed the small internal Planet My Arae d with a Uranus comparable mass and only a 9-day orbital period. Thus representing not only the first example of a now well-known as Hot Neptune -class exoplanets, but was the smallest exoplanet yet discovered around a main sequence star. Its surface temperature is likely to be about 900K. The discovery was made possible by high-precision measurements of the radial velocity My Araes with the spectrograph of the High Accuracy Radial velocity Planet Searcher ( HARPS ) at the La Silla Observatory of the European Southern Observatory.
2006, two independent teams came to the researchers Krzysztof Gozdziewski and Francesco Pepe to the conclusion it appears that a fourth planet must necessarily be present, orbiting the parent star in a nearly circular orbit once every 311 days. This new model of the My Arae system is based on other parameters for the previously discovered planets, whose orbits fail now much less eccentric. With the discovery of My Arae e the system rose to second known exosolaren planetary system with four planets. The other was 55 Cancri, but there is a fifth planet has been discovered by now.
Construction of the system
The My Arae system consists of an inner uranus major planets with an orbital period of 9 days and three other high-mass companions - probably gas giants - to wide, nearly circular orbits. These circular orbits are in contrast to the commonly observed in long-period exoplanets highly eccentric orbits. The innermost planet could be a so-called chthonic Planet - a hitherto hypothetical planet class that is created when a gas planet loses its shell under the influence of the solar wind and only the rocky core remains. An alternative theory suggests the planet has already formed in the innermost regions of the My Arae system as a terrestrial planet, so be a " super-Earth ".
The inner gas giant e and b are almost in a 1:2 ratio of orbital resonance and therefore influence strongly. However, not always been so that, since simulations show that such a system after 78 million years to become unstable. However, since the planetary system of My Arae is much older, this circulation time ratio can not have existed from the beginning. So there are still some questions to be clarified.
The search for protoplanetary disks did not yield any results. Should My Arae have a debris disk, which could be compared with our Kuiper belt, so this is too diffuse to be able to perceive it from the Earth can.
Life?
Of the companions My Araes the gas planet b moves within the habitable zone around its star - that zone, allowing the water in its liquid form. The strong gravity of the gas giant is likely to make the formation of Earth-like planets impossible here; which does not mean that could not prevail on large moons to My Arae b a life- friendly environment. Here, however, the question remains whether the mass of the moons would be large enough to hold a thick atmosphere - also a necessary condition for the existence of liquid water. In addition, the message received from B My Arae dose of ultraviolet radiation is too low to support the formation of biomolecules can. While Planet Earth e receives a comparable dose of ultraviolet radiation, however, is too hot to have moons with a covered water surface.