Astronomers have found two planets smaller than Neptune orbiting Sun-like stars 3,000 light-years from Earth, in the star cluster NGC 6811.
The discovery shows that planets can develop even in crowded clusters jam-packed with stars.
“Old clusters represent a stellar environment much different than the birthplace of the Sun and other planet-hosting field stars,” lead author Soren Meibom of the Harvard-Smithsonian Center for Astrophysics (CfA) said.
“And we thought maybe planets couldn’t easily form and survive in the stressful environments of dense clusters, in part because for a long time we couldn’t find them,” Meibom said.
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 the size to be determined.
Kepler-66b and Kepler-67b are both less than three times the size of Earth, or about three-fourths the size of Neptune (mini-Neptunes).
Kepler-66b and -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.
Kepler-66b and -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.
The findings are published in the journal Nature.