Astronomers have discovered a new exoplanet orbiting a star that is a rare solar twin - a star that is almost identical to the Sun in all respects.
Using ESO's HARPS planet hunter in Chile, along with other telescopes around the world, astronomers discovered three planets orbiting stars in the cluster Messier 67.
Although more than one thousand planets outside the Solar System are now confirmed, only a handful have been found in star clusters.
Planets orbiting stars outside the Solar System are now known to be very common.
These exoplanets have been found orbiting stars of widely varied ages and chemical compositions and are scattered across the sky.
Anna Brucalassi (Max Planck Institute for Extraterrestrial Physics, Garching, Germany), lead author of the new study, and her team wanted to find out more.
The team used the HARPS planet-finding instrument on ESO's 3.6-metre telescope at the La Silla Observatory.
They carefully monitored 88 selected stars in Messier 67 over a period of six years to look for the tiny telltale motions of the stars towards and away from Earth that reveal the presence of orbiting planets.
This cluster lies about 2500 light-years away in the constellation of Cancer (The Crab) and contains about 500 stars. Many of the cluster stars are fainter than those normally targeted for exoplanet searches and trying to detect the weak signal from possible planets pushed HARPS to the limit.
Three planets were discovered, two orbiting stars similar to the Sun and one orbiting a more massive and evolved red giant star.
The first two planets both have about one third the mass of Jupiter and orbit their host stars in seven and five days respectively. The third planet takes 122 days to orbit its host and is more massive than Jupiter.
The first of these planets proved to be orbiting a remarkable star-it is one of the most similar solar twins identified so far and is almost identical to the Sun. It is the first solar twin in a cluster that has been found to have a planet.
Two of the three planets are "hot Jupiters"-planets comparable to Jupiter in size, but much closer to their parent stars and hence much hotter. All three are closer to their host stars than the habitable zone where liquid water could exist.
