First Planets Found Around Sun-Like Stars in a Cluster

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Whitney Clavin 818-354-4673
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J.D. Harrington 202-358-5241
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News release: 2012-289 Sept. 14, 2012

First Planets Found Around Sun-Like Stars in a Cluster

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2012-289&cid=release_2012-289

PASADENA, Calif. -- NASA-funded astronomers have, for the first time, spotted planets
orbiting sun-like stars in a crowded cluster of stars. The findings offer the best evidence yet that
planets can sprout up in dense stellar environments. Although the newfound planets are not
habitable, their skies would be starrier than what we see from Earth.

The starry-skied planets are two so-called 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, also called the Praesepe, a collection of roughly 1,000 stars
that appear to be swarming around a common center.

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. The stars therefore 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 Mario R. Perez, the NASA astrophysics program scientist in the
Origins of Solar Systems Program. "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."

The two new Beehive planets are called Pr0201b and Pr0211b. The star's name followed by a "b" is the standard naming
convention for planets.

"These are the first 'b's' in the Beehive," said Sam Quinn, a graduate student in astronomy at
Georgia State University in Atlanta and the lead author of the paper describing the results, which
was published in the Astrophysical Journal Letters.

Quinn and his team, in collaboration with David Latham at the Harvard-Smithsonian Center for
Astrophysics, discovered the planets by using the 1.5-meter Tillinghast telescope at the
Smithsonian Astrophysical Observatory's Fred Lawrence Whipple Observatory near Amado,
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 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 relatively young age of the Beehive cluster makes these planets among the youngest
known," said Russel White, the principal investigator on the NASA Origins of Solar Systems
grant that funded this study. "And that's important because it sets a constraint on how quickly
giant planets migrate inward -- and knowing how quickly they migrate is the first step to figuring
out how they migrate."

The research team suspects 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.

According to White, "Searches for planets around nearby stars suggest that these metals act like
a 'planet fertilizer,' leading to an abundant crop of gas giant planets. Our results suggest this may
be true in clusters as well."

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages NASA's Exoplanet Exploration
Program office. More information about exoplanets and NASA's planet-finding program is
available at: http://planetquest.jpl.nasa.gov .

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