Astronomers Discover Two Beehive Planets

Astronomers have for the first time discovered planets orbiting Sun-like stars in a star cluster.

An artist’s impression of one of the two gas giant planets orbiting stars in the Beehive cluster (NASA / JPL-Caltech)

The planets dubbed Pr0201b and Pr0211b are hot Jupiters, which are massive, gaseous orbs that are boiling hot because they orbit tightly around their parent stars. Each hot Jupiter circles a different Sun-like star in the Beehive Cluster, a collection of roughly 1,000 stars. Although the planets are not habitable, their skies would be starrier than what we see from Earth.

The Beehive is an open cluster, or a grouping of stars born at about the same time and out of the same giant cloud of material. As such, the stars share a similar chemical composition. Unlike the majority of stars, which spread out shortly after birth, these young stars remain loosely bound together by mutual gravitational attraction.

“We are detecting more and more planets that can thrive in diverse and extreme environments like these nearby clusters,” said Dr Mario R. Perez, the NASA astrophysics program scientist in the Origins of Solar Systems Program and co-author of a paper describing the discovery published in the Astrophysical Journal Letters (arXiv.org version).

“Our galaxy contains more than 1,000 of these open clusters, which potentially can present the physical conditions for harboring many more of these giant planets,” Dr Perez said.

“These are the first ‘b’s’ in the Beehive,” said lead author Sam Quinn, a graduate student in astronomy at Georgia State University in Atlanta.

The team discovered the planets by using the 1.5-meter Tillinghast telescope at the Smithsonian Astrophysical Observatory’s Fred Lawrence Whipple Observatory in Arizona to measure the slight gravitational wobble the orbiting planets induce upon their host stars. Previous searches of clusters had turned up two planets around massive stars but none had been found around stars like our Sun until now.

This image points out the location of the planets Pr0201b and Pr0211b in the Beehive star (Stuart Heggie)

“This has been a big puzzle for planet hunters,” Quinn said. “We know that most stars form in clustered environments like the Orion nebula, so unless this dense environment inhibits planet formation, at least some Sun-like stars in open clusters should have planets. Now, we finally know they are indeed there.”

The results also are of interest to theorists who are trying to understand how hot Jupiters wind up so close to their stars. Most theories contend these blistering worlds start out much cooler and farther from their stars before migrating inward.

The research team suspects that planets were turned up in the Beehive cluster because it is rich in metals. Stars in the Beehive have more heavy elements such as iron than the Sun has.

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Bibliographic information: Samuel N. Quinn et al. 2012. Two “b”s in the Beehive: The Discovery of the First Hot Jupiters in an Open Cluster. ApJ 756, L33; doi: 10.1088/2041-8205/756/2/L33