European Southern Observatory (ESO) announced on August 24, 2010 the discovery of the lowest mass extrasolar planet discovered to date.
HD 10180 b orbits the solar type star HD 10180, which has properties and an age very similar to those of the Sun. HD 10180 also has a planetary system with the most planets of any extrasolar planetary system known so far.
The star lies in the southern constellation of Hydrus 127 light years away. Astronomers have confirmed the presence of five planets and have tantalising evidence of two more. The distance of the planets from their parent star follow a regular pattern, similar to that seen in our own solar system.
Christophe Lovis from Geneva University’s observatory in Switzerland was lead researcher on the study. ”We have found what is most likely the system with the most planets yet discovered,” said Dr Christophe Lovis.
”This remarkable discovery also highlights the fact that we are now entering a new era in exoplanet research: the study of complex planetary systems and not just of individual planets.”
”Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system,” he added.
Astronomers patiently studied it for six years using a planet-finding instrument called the HARPS spectrograph (High Accuracy Radial velocity Planet Searcher), attached to ESO’s 3.6 metre (11.8ft) telescope at La Silla, Chile.
From 190 individual HARPS measurements, they were able to detect tiny wobbles in the star’s motion caused by the gravitational tugs of its planets.
“If there is one planet it will induce a little movement – the star will come towards us and move away,” Dr Lovis explained to BBC News. “And what works for one [planet] works for many.”
The five strongest signals corresponded to planets with Neptune-like masses, between 13 and 25 times that of the Earth. These planets, with orbit periods ranging from six to 600 days, are separated from their star at 0.06 to 1.4 times the distance between the Earth and sun.
”We also have good reasons to believe that two other planets are present. One would be a Saturn-like planet (with a minimum mass of 65 Earth masses) orbiting in 2,200 days,” said Dr Lovis.
“The other would be the least massive exoplanet ever discovered, with a mass of about 1.4 times that of the Earth. It is very close to its host star, at just 2 per cent of the Earth-sun distance. One ‘year’ on this planet would last only 1.18 Earth days,” he added.
The planet would be rocky, like the Earth, but probably far too hot to sustain life. With at least five Neptune-sized planets circling inside an orbit equivalent to that of Mars, the HD 10180 system has a more populated inner region than our solar system.
Dr Lovis also said: “Studies of planetary motions in the new system reveal complex gravitational interactions between the planets and give us insights into the long-term evolution of the system.”
So far astronomers have found 15 systems containing at least three planets. The last record holder was 55 Cancri, which has a total of five planets including two gas giants.
Martin Dominik, an astronomer and exoplanet hunter from the UK’s University of St Andrews said the complexity and structure of this system made it an interesting discovery.
“The richness of the system of planets around HD 10180 with its many characteristic features marks the way forward towards gathering the information that will put our own existence into cosmic context,” he told BBC News.
He cautioned against describing this as the “richest system” saying that it was not clear whether other systems that had already been detected hosted further planets.
Dr Dominik added: “I am tempted to consider the detected system as one of the most ‘informative’ ones. Like most discoveries in science, the findings come with more questions than answers; but in my opinion, this is what really advances a field.” [ESO via Daily Telegraph and BBC]