Exoplanets, or planets orbiting stars outside the Solar System, are old news. Scientists have confirmed more than 1,000 of them, in fact. What's less common is finding planets orbiting star clusters, like Messier 67. Using ESO's HARPS planet hunter in Chile, astronomers have found three such planets and one of them, rarer still, orbits a solar twin - a star so similar to our Sun that it's nearly identical.
It's rare to find planets in star clusters, and scientists aren't sure why. After all, most stars form in such clusters, and it would be reasonable to expect then that more planets would be observed orbiting them. Astronomers speculate that there might be something different in the way that planets form around star clusters, but it's all conjecture at this point.
Scientists are thrilled to have found a planet orbiting a star so similar to our sun. "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 Max Planck Institute for Extraterrestrial Physics in Garching, Germany.
The HARPS planet hunter wasn't alone in its observations. Several other observatories worldwide contributed. All told, astronomers carefully monitored 88 selected stars in Messier 67 over a period of six years. Nearly imperceptible (yet telling) movements of the stars towards and away from Earth were what revealed the presence of orbiting planets.
Located in the Cancer constellation, two of the three newly discovered planets orbited stars similar to the Sun, while the third orbited an older red giant star. The first planet orbits what's believed to be the closest thing to the Sun's identical twin ever discovered - very similar in both age and composition. This is the first observation of a planet orbiting such a star within a cluster.
Don't get your hopes up for nearby alien life just yet - all three planets orbit much closer to their stars than Earth, putting them outside of the habitable zone where water could exist.