It took six years and a large international collaboration, but the result has more than repaid the efforts.
Using ESO’s planet hunter, HARPS (mounted on the 3.6 m ESO telescope at the La Silla Observatory, Chile), and correlating with data from other telescopes around the world, the team led by Anna Brucalassi (MPE, Garching, Germany) discovered three planets orbiting stars in the star cluster Messier 67, about 2500 light-years from Earth.
The importance of the discovery does not lie so much in the identification of the planets (more than a thousand planets have now been discovered and confirmed outside the Solar System), but in the fact that they were found in a star cluster. So far, only a few planets have been found in star clusters, which is particularly strange since it is known that most stars are born in clusters.
“In the star cluster Messier 67,” says Anna Brucalassi, “the stars are more or less the same age and composition as the Sun. This makes it a perfect laboratory to study how many planets form in this crowded environment and whether they preferentially form around more or less massive stars.”
Of the three planets identified, two are hot Jupiters orbiting Sun-like stars, while the third orbits a more massive and evolved red giant star. In particular, one of the first two planets orbits the star HIP 102152, the oldest known twin of the Sun.
“These new results show that planets in open clusters are almost as common as in isolated stars – but they are not easy to detect,” adds Luca Pasquini (ESO, Garching, Germany), co-author of the new paper. “The new results contrast with previous works that did not find planets in clusters, but they agree with other more recent observations. We are continuing to observe this cluster to discover how stars with and without planets differ in mass and chemical composition.”
The work is presented in a paper titled “Three planetary companions around M67 stars“, by A. Brucalassi et al., to be published by the journal Astronomy & Astrophysics.
All the info in the ESO release