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Kepler finds two planets with a striking resemblance to Earth

Kepler finds two planets with a striking resemblance to Earth
This artist's concept depicts an Earth-like planet orbiting an evolved star that has formed a stunning "planetary nebula." Earlier in its life, this planet may have been like one of the eight newly discovered worlds orbiting in the habitable zones of their stars. (David A. Aguilar / Harvard-Smithsonian Center for Astrophysics)

Welcome to the family! Scientists using NASA’s Kepler spacecraft have confirmed at least eight new roughly Earth-sized planets sitting in the habitable zones of their host stars – two of which rival the most "Earth-like" planets found to date.

The discoveries, described at the American Astronomical Society meeting in Seattle, come as astronomers announce a fresh influx of 554 candidate planets, bringing the total to 4,175 possible planets – at least 1,000 of which have now been confirmed.

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"Despite the fact that there are over 4,000 candidates from Kepler, there are still very few small, less-than-two-Earth-radius, habitable-zone planets," said coauthor Doug Caldwell, SETI Institute Kepler scientist at NASA's Ames Research Center. "They really make up a special population that is of interest for understanding the prevalence of life in the universe."

These two planets, described in research led by the Harvard-Smithsonian Center for Astrophysics, are named Kepler-438b and Kepler-442b. Both orbit red dwarf stars, which are much cooler and dimmer than our sun. That means that their habitable zone – the area around the star that's the right temperature for liquid water to exist without getting boiled or frozen – is much closer to the star.

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That's good news for these two planets, since Kepler-438b orbits its star every 35.2 days, and Kepler-442b circles its star once every 112 days – compare that with Earth, whose orbit takes 365 days. Kepler-438b gets about 40% more light than Earth (giving it a 70% chance of being in its star's habitable zone), and Kepler-442b receives roughly two-thirds as much light as Earth (giving it a 97% chance of being in its star's habitable zone).

Before Tuesday's announcement, the two most Earth-like planets were Kepler-186f (1.1 times Earth's size, with 32% a much light) and Kepler-62f (1.4 times Earth's size, with 41% as much light).

The scientists think the two new planets are around the right size to be rocky like Earth, rather than gassy like a mini-Neptune. But they can't say for sure nor can they say whether there is water present. Aside from size and estimated temperature, there aren't a whole lot of other qualities the astronomers can home in on. Still, it's a start, the researchers said.

"We're not only closing in on an Earth twin, but we're better understanding the diversity in this special neighborhood of planets," Caldwell said.

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