Nature article on frequency of planets inside and outside of open starclusters

27 June 2013. An international team of astronomers led by Soeren Meibom of the Harvard-Smithsonian Center for Astrophysics has found two planets smaller than Neptune orbiting Sun-like stars in the open star cluster NGC 6811. The discovery, published in the journal Nature, shows that planets can develop even in crowded clusters jam-packed with stars.
Nature article on frequency of planets inside and outside of open starclusters

Colour-magnitude and colour-period diagram for NGC6811. (Credit: AIP)

The two new alien worlds appeared in data from NASA's Kepler spacecraft. Kepler hunts for planets that transit, or cross in front of, their host stars. During a transit, the star dims by an amount that depends on the size of the planet, allowing its size to be determined. Kepler-66 and Kepler-67 are both less than three times the size of Earth, or about three-fourths the size of Neptune (mini-Neptunes).

Sydney Barnes, scientist at the Leibniz Institute for Astrophysics Potsdam (AIP) and co-author of the paper, explains: „The discovery presents two very well-characterized planetary systems, and suggests that small planets occur as frequently in star clusters as they do outside cluster environments. After studying NGC 6811 for several years, we have been able to prove that the planets belong to the cluster. This association helps to characterize the planets, for instance nailing their ages down as one billion years.“

Kepler-66 and -67 are the smallest planets to date found in a star cluster, and the first cluster planets seen to transit their host stars, which enables the measurement of their sizes. Kepler-66 and Kepler-67 therefore join a small group of planets with precisely determined ages, distances, and sizes.

Considering the number of stars observed by Kepler in NGC 6811, the detection of two such planets implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars (stars not within a cluster or association) in the Milky Way galaxy.

(Text based on CFA press release)


Nature article

Press release Harvard-Smithsonian Center for Astrophysics (CFA)


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The key areas of research at the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP has been a member of the Leibniz Association since 1992.