Two New Planets In Hostile Star Cluster
June 26, 2013

Astronomers Find Two New Planets Inside Hostile Star Cluster

Lee Rannals for - Your Universe Online

Astronomers have discovered two planets smaller than Neptune in the midst of a hostile star cluster environment.

Stars kick off their lives in clusters where they fight for room along with thousands of neighbors in an environment surrounded by strong radiation and harsh stellar winds. Astronomers say they found two planets packed into the harsh environment of the star cluster NGC 6811.

“Old clusters represent a stellar environment much different than the birthplace of the Sun and other planet-hosting field stars,” says Soren Meibom, of the Harvard-Smithsonian Center for Astrophysics (CfA) and lead author of the paper published in the journal Nature.

“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.”

The new alien worlds appeared in data from NASA's offline Kepler spacecraft, which was used to help sniff out exoplanets. Kepler is no longer watching out for exoplanets due to a malfunction, but it has collected plenty of data over the years that will keep researchers busy for years to come.

When a far away planet passes between Earth and a star, the light from the star slightly dips, and scientists can then use the magnitude of this dip to determine the size of the exoplanet. Astronomers believe the newly discovered planets, Kepler-66b and Kepler-67b, are less than three times the size of Earth, or about three-fourths the size of Neptune.

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. More than 850 known planets outside our solar system have been discovered, but only four of those are similar to or greater than Jupiter in mass.

Astronomers estimate that NGC 6811 is about a billion-years-old. Since scientists know the age of this star cluster, it also allows the them to determine the age, distance and size of Kepler-66b and Kepler-67b.

The detection of the planets implies that the frequency and properties of planets in open clusters are consistent with those planets around field stars in the Milky Way Galaxy.

“These planets are cosmic extremophiles,” says Meibom. “Finding them shows that small planets can form and survive for at least a billion years, even in a chaotic and hostile environment.”

Another group of astronomers recently announced that they had found a record-breaking planetary system with at least six planets, three of which are Super Earths. The "habitable zone" around Gliese 667C is completely full, leaving no more room for another planet to exist. This zone is the perfect distance between a planet and its host star where liquid water could be found.