The planets are too close to their host stars for liquid water, a condition believed to be necessary for life, and they are unlikely to even be solid bodies. Nevertheless, the study expands the domain where small planets can exist.
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So far, the only place where planets haven't been found yet is in globular clusters, an environment even more extreme that open clusters like NCG 6811.
"There is a threshold for when you cannot form planets or you make very different planets," Meibom told Discovery News.
Astronomers believe most, if not all, stars started off in clusters, which then collapsed over time. Some member stars gradually drifted off, becoming field stars, taking their planets along with them.
What was unknown is if the most commonly found planets in the galaxy, the super-Earths and mini-Neptunes (none of which ironically appear in our own solar system) could survive all the gravitational elbowing, radiation bombardment, supernova explosions and other conditions resulting from so many stars being jammed into a relatively small slice of celestial real estate.