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Star cluster survey reveals exoplanets

New source Astronomers have found a potentially rich source of exoplanets — those in solar systems other than our own — in stellar masses known as star clusters.

Hundreds of exoplanets have been found since the first was spotted in 1995, but very few have been found inside star clusters, where hundreds of stars, often born at the same time, gather in the same neighbourhood of the galaxy.

That rarity prompted experts to wonder if there was something in star clusters that disrupted the formation of planets from clumps of dust and gas.

But astronomers using an exoplanet-hunting instrument at the European Southern Observatory (ESO) in the Chilean desert have found that planets are probably just as common in star clusters.

Over six years, they monitored 88 promising-looking stars in a formation called Messier 67, a cluster of about 500 stars located some 2500 light years away in the constellation of Cancer.

"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," says lead author of the study Anna Brucalassi of the Max Planck Institute for Extraterrestrial Physics, Germany.

The trawl netted three intriguing planets.

Two of the three are 'hot Jupiters' — planets comparable to Jupiter in size, but much closer to their parent stars and hence much hotter.

The other orbits a star that is a near-twin to the Sun, which is a very rare find in exoplanet searchers. But it orbits at such close proximity that the temperature would be scorching. Water, the stuff of life as we know it, could not exist in liquid form.

"These new results show that planets in open star clusters are about as common as they are around isolated stars, but they are not easy to detect," says Luca Pasquini, who is based with ESO in Garching, Germany.

"We are continuing to observe this cluster to find how stars with and without planets differ in mass and chemical makeup."