Astronomers have found two planets smaller than three times the size of Earth orbiting sun-like stars in a crowded stellar cluster approximately 3,000 light-years from Earth in the constellation Cygnus.
This finding demonstrates that small planets can form and persist in a densely packed cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars not associated with clusters, like our sun, in the galaxy. The paper was published June 26, 2013, in the journal Nature.
"These planets are cosmic extremophiles," said lead author Soren Meibom of the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Mass. "Finding them shows that small planets can form and survive for at least a billion years, even in a chaotic and hostile environment."
Of the more than 850 known planets beyond our solar system, only four - all similar to or greater than Jupiter in mass – were found in clusters. Kepler-66b and Kepler-67b are the smallest planets to be found in a star cluster, and the first cluster planets seen to transit their host stars, which enables the measurement of their sizes.