The ESO used its HARP instrumentation on a 3.6-meter-long telescope at the La Silla Observatory to locate the planets. Using data from other observatories, the ESO monitored 88 stars in the Messier 67 cluster over a period of six years. They calculated small movements that revealed the presence of these three planets.
“In the Messier 67 star cluster the stars are all about the same age and composition as the Sun. This makes it a perfect laboratory to study how many planets form in such a crowded environment, and whether they form mostly around more massive or less massive stars,” said Anna Brucalassi of the Max Planck Institute for Extraterrestrial Physics.
Two of the planets were orbiting stars similar to the Sun, with one orbiting a star almost identical to it. These planets were a third the mass of Jupiter. The planet orbiting the solar twin took seven days to do so, while the other took five days to orbit its star.
The third planet was orbiting a giant red star, was larger than Jupiter and took 122 days to complete its orbit.
The Messier 67 cluster contains 500 stars and is about 2,500 light-years away in the constellation Cancer. The findings show that planets are as common in star clusters as they are in isolated star systems.
"The new results are in contrast to earlier work that failed to find cluster planets, but agrees with some other more recent observations. We are continuing to observe this cluster to find how stars with and without planets differ in mass and chemical makeup," said Luca Pasquini of the ESO.