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Unusually high number of hot Jupiters found in star cluster

Astronomers spotted an unexpectedly high number of “hot Jupiter” exoplanets in the Messier 67 star cluster.

Scientists have located an unexpected number of “hot Jupiter” exoplanets in the star cluster known as Messier 67.

Tech Times explains that so-called hot Jupiters are large planets that orbit their stars at a very close distance.  While Jupiter itself takes twelve Earth years to orbit the sun, hot Jupiters are in such tight orbits that they take fewer than ten Earth days to complete one orbit around their host stars.

Scientists believe that these super-hot exoplanets form at a greater distance from their stars and then spiral closer into their short orbit distances.  Until the recent discovery of a number of hot Jupiters in Messier 67, it was thought that the gas giants would not be able to form in a dense open star cluster.

Using data from an assortment of telescopes and instruments, primarily the European Southern Observatory’s (ESO) High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, researchers were able to determine that hot Jupiters appeared more often around stars in the Messier 67 cluster than near stars outside of clusters.

“No hot Jupiters at all had been detected in open clusters until a few years ago,” Luca Pasquini of the ESO said.  “In three years the paradigm has shifted from a total absence of such planets – to an excess!”

“This is really a striking result,” Anna Brucalassi of the Max Planck Institute said in a statement. “The new results mean that there are hot Jupiters around some 5% of the Messier 67 stars studied — far more than in comparable studies of stars not in clusters, where the rate is more like 1%.”

The team suspects that the densely packed stars in the cluster may have pushed the giant planets closer together.

“We want to use an open star cluster as a laboratory to explore the properties of exoplanets and theories of planet formation,” Roberto Saglia of the Max Planck Institute said. “Here we have not only many stars possibly hosting planets, but also a dense environment, in which they must have formed.”

The study was published the journal Astronomy & Astrophysics.