Scientists on Monday reported they had discovered a rocky "mega-Earth" that expands the definition of planets beyond our solar system that could potentially host life.
The new type of planet, Kepler-10c, weighs 17 times as much as Earth. Researchers previously thought this kind of world could not exist since any planet that large would attract hydrogen gas, becoming a gas giant like Jupiter rather than a solid planet.
“Finding Kepler-10c tells us that rocky planets could form much earlier than we thought. And if you can make rocks, you can make life,” said Harvard-Smithsonian researcher Dimitar Sasselov in a media release.
Kepler-10c isn't the only potentially habitable (or inhabited) planet out there. The Planetary Habitability Laboratory run by the University of Puerto Rico at Arecibo maintains a list of exoplanets that are most similar to Earth, taking size, mass, and distance from their host stars into consideration — factors that are likely to support liquid water and would be conducive to life as we know it.
The catalog does not guarantee that these planets host life but "lists the best candidates so far for potential habitable worlds and the objects of interest for the search of life outside the Solar System."
Here's a look at some of the top candidates from the catalog, ranked in order of Earth similarity.
12. Gliese-581d
Gliese-581d is one of five planets to be discovered orbiting red dwarf star Gliese 581. It is bigger than 581g, with a mass at least seven times Earth's and twice as big in size.
The planet orbits on the outer edge of the habitable zone and could be warm enough to support clouds, oceans, and rain.
11. Kepler 186f
One of the latest additions to the catalog is Kepler-186f, which is 450 light-years away and is the most Earth-like in size to be found in the habitable zone of its star.
The newly-found planet, described as "Earth's cousin," is about 10% larger than Earth and could have liquid water on its surface. That water may be frozen since it orbits the outer edge of the habitable zone. Its host star is also cooler and much smaller than our sun.
Scientists still don't know what Kepler 186f is made of, but think it could have a rocky surface like Earth. Ready to go?
10. Kepler-62f
Kepler-62f is the second potentially habitable planet found orbiting the sun-like Kepler 62, discovered April 18, 2013.
The planet is smaller than Kepler-62e at 1.41 times the radius of our planet.
Scientists think Kepler-62f could be rocky, based on observations of exoplanets that are similar in size.
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